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Institute
- Institut für Botanik und Landschaftsökologie & Botanischer Garten (135) (remove)
Publisher
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Forest ecosystems around the world and especially boreal forests, are facing
drastically changing climatic conditions. It is known that these changes could
challenge their functionality and vitality. Still, the exact impact is not fully
understood, as tree growth is a complex process and depends on countless
environmental and genetic factors. To estimate the effects of climate change
on tree growth and forest development precisely, we must learn more about
tree growth itself. A comprehensive approach is needed where trees and
forests are investigated on different scales and levels of detail, ranging from
global studies to studies on single individuals.
In this dissertation, I follow such a comprehensive approach, using the
North American conifer white spruce as an example. I present three papers
in the form of three chapters in which my co-authors and I studied the
growth and anatomy of white spruce (Picea glauca [Moench] Voss) and how
it is influenced by environmental, climatic, and genetic factors.
We used diverse approaches and methods on different spatial scales, ranging from
investigations on the landscape to the local scale. We established three paired
plots with forest and treeline sites (two cold-limited and one drought-limited).
as well as one additional forest site. In the first chapter, we concentrated
on the genetic diversity of white spruce within and between populations at
all study sites throughout Alaska. The genetic investigations were combined
with analyses on the individual growth response of trees to climatic conditions
to find whether genetic similarities or spatial proximity caused similarities
in growth and climatic sensitivity. In the second chapter, we studied the
direct and indirect effects of environmental conditions on the xylem tissue
of white spruce. We analyzed the impact of precipitation, temperature, and
tree height on four xylem anatomical traits in trees growing at the three
treelines. The investigated traits represented the main functions of xylem
tissue (i.e., water transport and structural support). In the third chapter,
we investigated similar xylem anatomical traits at one cold-limited treeline.
We compared xylem anatomy and annual increment between genetic groups
and individuals and between spatial groups to investigate whether spatial or
genetic grouping influenced the anatomy and growth of white spruce.
We found an overall high gene flow and high genetic diversity in white
spruce. However, the sensitivity of the growth and anatomical traits of white
spruce was driven mainly by spatial rather than genetic effects and differed
between study sites. Trees from the drought-limited site were more sensitive
towards precipitation and a moisture index, while trees from the cold-limited
sites were more sensitive towards temperature. A strong direct effect of tem-
perature was primarily found in latewood traits related to the structural sup-
port of the tree. Earlywood traits related to water transport, however, were
influenced mainly by tree height. Tree height itself was potentially affected
by diverse abiotic and biotic factors (e.g., (micro)climate, soil conditions,
and competition). Thus, traits related to water transport were indirectly
influenced by environmental conditions. Genetic effects in xylem anatomical
traits were found in the earlywood hydraulic diameter and latewood den-
sity, whereas in general, primarily spatial rather than genetic grouping was
influencing the anatomy of white spruce.
Overall, white spruce showed to be a genetically diverse species with a
high gene flow. The effects of spatial proximity and spatial grouping on the
sensitivity and anatomy of white spruce indicate high phenotypic plastic-
ity. This high phenotypic plasticity combined with the vast genetic diversity
translates into an immense potential for the species to adjust (phenotypically)
and possibly adapt (genetically) to changing conditions. Thus, in terms of
climate change, white spruce may be a rather persistent species that manages
to cope with the drastic changes. Though additional work might be needed to
draw a more solid conclusion, the presented work shows how a comprehensive
study approach can help to interpret and understand the growth and ecology
of a tree species. It may be an inspiration for future studies to broaden their
approaches and to use comprehensive methods on different levels of detail to
not only observe trees but to explore and understand them.
Abstract
Individuals of the marine chelicerate lineage Pycnogonida (sea spiders) show considerable regenerative capabilities after appendage injury or loss. In their natural habitats, especially the long legs of sea spiders are commonly lost and regenerated, as is evidenced by the frequent encounter of specimens with missing or miniature legs. In contrast to this, the collection of individuals with abnormally developed appendages or trunk regions is comparably rare. Here, we studied a remarkable malformation in a postlarval instar of the species Phoxichilidium femoratum (Rathke, 1799) and describe the external morphology and internal organization of the specimen using a combination of fluorescent histochemistry and scanning electron microscopy. The individual completely lacks the last trunk segment with leg pair 4 and the normally penultimate trunk segment bears only a single aberrant appendage resembling an extension of the anteroposterior body axis. Externally, the proximal units of the articulated appendage are unpaired, but further distally a bifurcation into two equally developed leg‐like branches is found. Three‐dimensional reconstruction of the musculature reveals components of two regular leg muscle sets in several of the proximal articles. This confirms interpretation of the entire appendage as a malformed leg and reveals an externally hidden paired organization along its entire proximodistal axis. To explain the origin of this unique malformation, early pioneering studies on the regenerative potential of pycnogonids are evaluated and (a) an injury‐induced partial fusion of the developing limb buds of leg pair 3, as well as (b) irregular leg regeneration following near complete loss of trunk segments 3 and 4 are discussed. Which of the two hypotheses is more realistic remains to be tested by dedicated experimental approaches. These will have to rely on pycnogonid species with established laboratory husbandry in order to overcome the limitations of the few short‐term regeneration studies performed to date.
Changes in the environment will alter the growth rate of trees and forests. Different disciplines assess such growth rates differently, for example, with tree-ring width data, forest inventories or with carbon-flux data from eddy covariance towers. Such data is used to quantify forests biomass increment, forest’s carbon sequestration or to reconstruct environmental variables before instrumental records. However, raw measurement data is typically not considered to be representative for the average growth rate of trees or forests. Depending on the research question, the effects of certain environmental variables or effects of tree and forest structure have to be removed first. It can be challenging to define and quantify a growth trend that can answer a specific research question because trees and forests grow and respond to environmental change in multiple ways simultaneously, for example, with altered radial increment, height growth, and stand density. Further challenges pose time-lagged feedback loops, for example, between height and radial increment or between stand density and radial increment. Generally, different environments will lead to different tree and forest structures, but because of tree’s longevity this adaptation to the new environment will take decades or even centuries. Consequently, there can be an offset between the present forest structure and what we term the potential natural forest (PNF): Similar to the potential natural vegetation (PNV), the PNF represents that forest that would develop under the current environmental conditions in the absence of human intervention. Because growth rates are affected by the tree and forest structure, growth-trend estimates will differ between the present and the potential forest. Consequently, if the legacy effects of the past are not of interest, the PNF is the theoretical baseline to correct and estimate growth trends.
Rewetting is the most effective way to reduce greenhouse gas (GHG) emissions from drained peatlands and must significantly contribute to the implementation of the Paris Agreement on Climate within the land sector. In 2010–2013, more than 73 thousand hectares of fire-prone peatlands were rewetted in the Moscow Region (the hitherto largest rewetting program in the Northern Hemisphere). As the Russian Federation has no national accounting of rewetted areas yet, this paper presents an approach to detect them based on multispectral satellite data verified by ground truthing. We propose that effectively rewetted areas should minimally include areas with wet grasslands and those covered with water (cf. the IPCC categories “rewetted organic soils” and “flooded lands”). In 2020, these lands amounted in Moscow Region to more than 5.3 and 3.6 thousand hectares, respectively. Assuming that most rewetted areas were former peat extraction sites and using IPCC default GHG emission factors, an overall GHG emission reduction of over 36,000 tCO2-eq year−1 was calculated. We furthermore considered the uncertainty of calculations. With the example of a 1535 ha large rewetted peatland, we illustrate the estimation of GHG emission reductions for the period up to 2050. The approach presented can be used to estimate GHG emission reductions by peatland rewetting on the national, regional, and object level.
Agriculture in the populated islands of the Galapagos Archipelago, a protected area due to its unique biodiversity, has been detrimental to its conservation but highly required to meet food necessities. A potential solution to make agricultural farming more sustainable is adopting water-saving technologies (WSTs). Therefore, this study aimed to test the effectiveness of using WSTs such as Groasis Waterboxx® in three of the most valuable crops in the islands through participatory research with the involvement of a group of farmers from the Floreana and Santa Cruz islands and explore a possible transition to more sustainable agricultural practices. Capsicum annuum, Cucumis sativus and Solanum lycopersicum were cultivated using Groasis Waterboxx® and compared to conventional irrigation practices (drip-irrigated controls) to assess the variability of productivity, the number of fruits and individual fruit weight (IFW). In addition, differences in plant traits were analyzed by crop, and island. Results suggested that WSTs such as Groasis Waterboxx® may provide on-farm benefits regarding the yields of the studied traits. From this study, it is difficult to determine whether participation in such a research study will permanently change irrigation practices. However, the participant’s responses to the study suggest an increase in their understanding of the use and benefits of WST.
Plant roots influence many ecological and biogeochemical processes, such as carbon, water and nutrient cycling. Because of difficult accessibility, knowledge on plant root growth dynamics in field conditions, however, is fragmentary at best. Minirhizotrons, i.e. transparent tubes placed in the substrate into which specialized cameras or circular scanners are inserted, facilitate the capture of high-resolution images of root dynamics at the soil-tube interface with little to no disturbance after the initial installation. Their use, especially in field studies with multiple species and heterogeneous substrates, though, is limited by the amount of work that subsequent manual tracing of roots in the images requires. Furthermore, the reproducibility and objectivity of manual root detection is questionable. Here, we use a Convolutional Neural Network (CNN) for the automatic detection of roots in minirhizotron images and compare the performance of our RootDetector with human analysts with different levels of expertise. Our minirhizotron data come from various wetlands on organic soils, i.e. highly heterogeneous substrates consisting of dead plant material, often times mainly roots, in various degrees of decomposition. This may be seen as one of the most challenging soil types for root segmentation in minirhizotron images. RootDetector showed a high capability to correctly segment root pixels in minirhizotron images from field observations (F1 = 0.6044; r2 compared to a human expert = 0.99). Reproducibility among humans, however, depended strongly on expertise level, with novices showing drastic variation among individual analysts and annotating on average more than 13-times higher root length/cm2 per image compared to expert analysts. CNNs such as RootDetector provide a reliable and efficient method for the detection of roots and root length in minirhizotron images even from challenging field conditions. Analyses with RootDetector thus save resources, are reproducible and objective, and are as accurate as manual analyses performed by human experts.
In terms of climate change and climate change mitigation, the quantitative knowledge of global carbon pools is important information. On the one hand, knowledge on the amount of carbon cycling among – and stored in – global pools (i.e. Atmosphere, Biosphere, Cryosphere, Hydrosphere, and Lithosphere) may improve the reliability of models predicting atmospheric CO2 concentrations in terms of fossil fuel combustion. On the other hand, the carbon sequestration potential of specific ecosystems allows for estimating their feasibility regarding carbon trade mechanisms such as the Clean Development Mechanism or the Reducing Emissions from Deforestation and Degradation Program (REDD+). However, up to date, the majority of terrestrial carbon assessments have focused on forests and peatlands, leaving a data gap open regarding the remaining ecosystems. This data gap is likely to be explained by the relatively high carbon densities and/or productivities of forests and peatlands. Nevertheless, to get a precise as possible global picture, information on carbon pools and sequestration of other ecosystems is needed. Although desert ecosystems generally express low carbon densities, they may absolutely store a remarkable amount of carbon due to their large areal extent. In this context, Central Asian Deserts (in particular within the Turanian Deserts, i.e. Karakum, Kysylkum, Muyunkum) likely inhibit comparably high carbon pools as they express a sparse vegetation cover due to an exceptionally high annual precipitation if compared to the World’s deserts. In this dissertation, three important woody plant species – Populus euphratica and Haloxylon aphyllum and Haloxylon persicum – of Central Asian Deserts were investigated for their carbon pools and carbon sequestration potential. These species were chosen as they I) locally express high carbon densities, II) are dominant species, III) have a rather large spatial distribution, and IV) have experienced a strong degradation throughout the 20th century. Thus, they likely show a remarkable potential for carbon re-sequestration through restoration and thus for an application of carbon trade mechanisms (CHAPTER I). P. euphratica was investigated in the nature reserve Kabakly at the Amu Darya, Turkmenistan and in Iminqak at the Tarim He, Xinjiang, China. The assessment of Haloxylon species was restricted to the Turanian deserts west of the Tain Shan. To achieve a first scientific basis for large scale estimates, different methodologies, ranging from allometric formulas, over dendrochronology to remote sensing were combined (CHAPTERS II-V). In CHAPTER II allometric formulas were successfully developed for Haloxylon aphyllum and Haloxylon persicum and applied to six study sites distributed over the Turanian Deserts to represent the allometric variability of Haloxylon species in Central Asia. CHAPTER III derives another allometric formula (only based on canopy area) for H. aphyllum and combines it with a remote sensing analysis from the nature reserve Repetek. Thereby, a first large scale estimate covering the Northeastern Karakum Desert of carbon pools related to mono specific H. aphyllum stands is achieved. CHAPTER IV describes the wood structure of Populus euphratica forests in the nature reserve Kabakly (Turkmenistan) and in Iminqak (Xinjiang, China). In CHAPTER V a dendrochronological approach derives models for predicting the Net Primary Productivity (NPP) and the age of P. euphratica in the nature reserve Kabakly. Thereby, a first feasibility assessment regarding remote sensing analyses and the upscaling of the obtained NPP results is carried out. First estimates based on these local studies (CHAPTER VI), reveal carbon densities ranging from 0.1 – 26.3 t C ha 1 for the three investigated species. Highest maximum and median carbon densities were found for P. euphratica, but Haloxylon aphyllum expressed remarkable maximum carbon densities (13.1 t C ha-1), too. The total carbon pools were estimated at 6480 kt C for P. euphratica, 520 kt C for H. aphyllum stands and 6900 kt C for Haloxylon persicum shrubland. Accounting for the extent of degraded areas, the total re-sequestration potentials of the respective species were estimated at 4320 kt C, 1620 kt C and 21900 kt C, this highlighting the remarkable absolute re-sequestration potential of H. persicum shrubland despite its low average carbon densities. In the end, the main results were put into a broader context (CHAPTER VI), discussing the general feasibility of reforestations both in ecological terms as well as in terms of carbon trade mechanisms. A short example highlights the strong connection between the feasibility of reforestations and the global carbon market. Finally, open research questions are brought forth revealing the yet large research potential of Central Asian Desert ecosystems in general and in terms of carbon sequestration.
A massive shift in agricultural practices over the past decades, to support exceptionally high yields and productivities involving intensive agriculture, have led to unsustainable agriculture practices across the globe. Sustenance of such high yields and productivities demand high use of organic and industrial fertilizers. This acts as a negative pressure on the environment. Excessive use of fertilizers leads to nutrient surplus in the fields, which, as a part of catchment runoff, flows into the water bodies as diffuse pollution. These nutrients through rivers are eventually passed into seas. High nutrients ending up into water bodies cause eutrophication. The situation is worsened when such unsustainable agricultural activities are carried out on drained peatlands. As a result, the nutrients that were not part of the nutrient cycle in the landscape for years begin to leach out due to mineralization of peatlands, thereby putting an additional load of nutrients on the environment, that was already under the negative impact of nutrient surplus. In view of the above, a small lowland catchment of the Ryck river in northeast Germany was assessed for its nitrogen losses from agricultural lands through empirical modelling. Initial empirical modelling resulted in an average annual total nitrogen loss of 14.7 kg ha−1 year−1. After a comparative analysis of these results with procured data, the empirical equation was modified to suit the catchment, yielding more accurate results. The study showed that 75.6% of peatlands in the catchment are under agricultural use. Subsequently, a proposal was made for potential wetland buffer zones in the Ryck catchment. Altogether, 13 peatland sites across 8 sub-catchments were recommended for mitigation of high nutrient runoff. In the end, nutrient efficiency of proposed WBZs in one of the sub-catchments of Ryck has been discussed. The results show that (i) the modified empirical equation can act as a key tool in application-based future strategies for nitrogen reduction in the Ryck catchment, (ii) restoration of peatlands and introduction of WBZs can help in mitigating the nutrient runoff for improved water quality of Ryck, and subsequently (ii) contribute to efficient reduction of riverine loads of nutrients into the Baltic Sea.
Summary
Sphagnum farming can substitute peat with renewable biomass and thus help mitigate climate change. Large volumes of the required founder material can only be supplied sustainably by axenic cultivation in bioreactors.
We established axenic in vitro cultures from sporophytes of 19 Sphagnum species collected in Austria, Germany, Latvia, the Netherlands, Russia, and Sweden: S. angustifolium, S. balticum, S. capillifolium, S. centrale, S. compactum, S. cuspidatum, S. fallax, S. fimbriatum, S. fuscum, S. lindbergii, S. medium/divinum, S. palustre, S. papillosum, S. rubellum, S. russowii, S. squarrosum, S. subnitens, S. subfulvum and S. warnstorfii. These species cover five of the six European Sphagnum subgenera; namely, Acutifolia, Cuspidata, Rigida, Sphagnum and Squarrosa.
Their growth was measured in suspension cultures, whereas their ploidy was determined by flow cytometry and compared with the genome size of Physcomitrella patens. We identified haploid and diploid Sphagnum species, found that their cells are predominantly arrested in the G1 phase of the cell cycle, and did not find a correlation between plant productivity and ploidy. DNA barcoding was achieved by sequencing introns of the BRK1 genes.
With this collection, high‐quality founder material for diverse large‐scale applications, but also for basic Sphagnum research, is available from the International Moss Stock Center.
Abstract
In the 21st century, most of the world’s glaciers are expected to retreat due to further global warming. The range of this predicted retreat varies widely as a result of uncertainties in climate and glacier models. To calibrate and validate glacier models, past records of glacier mass balance are necessary, which often only span several decades. Long-term reconstructions of glacier mass balance could increase the precision of glacier models by providing the required calibration data. Here we show the possibility of applying shrub growth increments as an on-site proxy for glacier summer mass balance, exemplified by Salix shrubs in Finse, Norway. We further discuss the challenges which this method needs to meet and address the high potential of shrub growth increments for reconstructing glacier summer mass balance in remote areas.
The cultivation of common reed (Phragmites australis) is one of the most promising practices of paludiculture on fen peatlands. This highly productive grass has a high adaptation capacity via high levels of genetic diversity and phenotypic plasticity. In this study, a reed experimental site established on a degraded fen in 1996/97 with a mixture of monoclonally (meristematically propagated plantlets) and polyclonally (pre-grown seedlings) planted plots was investigated by microsatellite genotyping. All nine genotypes of the monoclonal planted plots were recovered and could be genetically characterized; invasion by other genotypes was negligible. Similarly, the polyclonal plots sustained high clonal diversity with no prevalence of a single genotype. The growth characteristics of the five quantitatively investigated genotypes significantly differed from each other (α = 0.05): dry biomass per stem 5–18 g, panicles per m2 20–60, average stem diameter 3.5–6 mm, height 170–250 cm. Similarly, the persistence of genotypes at the planted plots and their invasiveness (ability to invade neighboured plots) varied. These results show that common reed stands are extremely persistent even if established with genotypes that are likely not to be locally adapted. Their genetic structure remained stable for at least 24 years regardless of the planting density (1, 4, and 10 plants per m2). Our results indicate that farmers may be able to maintain favourable genotypes for many years, thus the selection and breeding of common reed as a versatile crop for rewetted peatlands is a promising objective for paludiculture research.
Climate Change-Induced Shift of Tree Growth Sensitivity at a Central Himalayan Treeline Ecotone
(2018)
Tree growth at northern boreal treelines is generally limited by summer temperature, hence tree rings serve as natural archives of past climatic conditions. However, there is increasing evidence that a changing summer climate as well as certain micro-site conditions can lead to a weakening or loss of the summer temperature signal in trees growing in treeline environments. This phenomenon poses a challenge to all applications relying on stable temperature-growth relationships such as temperature reconstructions and dynamic vegetation models. We tested the effect of differing ecological and climatological conditions on the summer temperature signal of Scots pine at its northern distribution limits by analyzing twelve sites distributed along a 2200 km gradient from Finland to Western Siberia (Russia). Two frequently used proxies in dendroclimatology, ring width and maximum latewood density, were correlated with summer temperature for the period 1901–2013 separately for (i) dry vs. wet micro-sites and (ii) years with dry/warm vs. wet/cold climate regimes prevailing during the growing season. Differing climate regimes significantly affected the temperature signal of Scots pine at about half of our sites: While correlations were stronger in wet/cold than in dry/warm years at most sites located in Russia, differing climate regimes had only little effect at Finnish sites. Both tree-ring proxies were affected in a similar way. Interestingly, micro-site differences significantly affected absolute tree growth, but had only minor effects on the climatic signal at our sites. We conclude that, despite the treeline-proximal location, growth-limiting conditions seem to be exceeded in dry/warm years at most Russian sites, leading to a weakening or loss of the summer temperature signal in Scots pine here. With projected temperature increase, unstable summer temperature signals in Scots pine tree rings might become more frequent, possibly affecting dendroclimatological applications and related fields.
Determining the effect of a changing climate on tree growth will ultimately depend on our understanding of wood formation processes and how they can be affected by environmental conditions. In this context, monitoring intra-annual radial growth with high temporal resolution through point dendrometers has often been used. Another widespread approach is the microcoring method to follow xylem and phloem formation at the cellular level. Although both register the same biological process (secondary growth), given the limitations of each method, each delivers specific insights that can be combined to obtain a better picture of the process as a whole. To explore the potential of visualizing combined dendrometer and histological monitoring data and scrutinize intra-annual growth data on both dimensions (dendrometer → continuous; microcoring → discrete), we developed DevX (Dendrometer vs. Xylogenesis), a visualization application using the “Shiny” package in the R programming language. The interactive visualization allows the display of dendrometer curves and the overlay of commonly used growth model fits (Gompertz and Weibull) as well as the calculation of wood phenology estimates based on these fits (growth onset, growth cessation, and duration). Furthermore, the growth curves have interactive points to show the corresponding histological section, where the amount and development stage of the tissues at that particular time point can be observed. This allows to see the agreement of dendrometer derived phenology and the development status at the cellular level, and by this help disentangle shrinkage and swelling due to water uptake from actual radial growth. We present a case study with monitoring data for Acer pseudoplatanus L., Fagus sylvatica L., and Quercus robur L. trees growing in a mixed stand in northeastern Germany. The presented application is an example of the innovative and easy to access use of programming languages as basis for data visualization, and can be further used as a learning tool in the topic of wood formation and its ecology. Combining continuous dendrometer data with the discrete information from histological-sections provides a tool to identify active periods of wood formation from dendrometer series (calibrate) and explore monitoring datasets.
Abstract
Monitoring the general public's support toward wildlife species is a strategy to identify whether a specific human–wildlife conflict (HWC) is escalating or de‐escalating over time. The support can change due to multiple factors, such as mass media news of HWC or providing information about ecological traits of a species. Methods such as the rating scale (RS) and the allocation of a fixed amount of money (money allocation [MA]) have been used in the human–wildlife dimension as a proxy to measure support toward wildlife species. We compared these two methods' capacity to assess the general public's support changes toward wildlife species in an experimental design setting. Face‐to‐face interviews were applied among urban dwellers (n: 359) in Valdivia, Chile. In each interview, the support toward 12 wildlife species was elicited using an RS and MA methods, on two occasions, before and after disclosing ecological traits of the species. The results indicate that the MA grouped the wildlife species based on shared ecological traits, information disclosed to the participants, while the RS did not obtain the same results. Specifically, the MA identified an increase and decrease of support toward the wildlife species, and the RS only an increment of support. These results could be partly explained due to the conceptual foundation of each method. The MA was designed to elicit preferences in a constrained choice, while the RS measures attitudes. As a constrained choice, the MA does allow maximum support to be given to one species only if all other species are left unsupported, while in the RS, it is possible to provide maximum support for all species. The mentioned characteristics of the MA make it more suitable than the RS when the objective is to identify support changes.
Abstract
Climate change will lead to more frequent and severe drought periods which massively reduce crop production worldwide. Besides drought, nitrogen (N)‐deficiency is another critical threat to crop yield production. Drought and N‐deficiency both decrease photosynthesis and induce similar adaptive strategies such as longer roots, reduction of biomass, induction of reactive oxygen species (ROS), and antioxidative enzymes. Due to the overlapping response to N‐deficiency and drought, understanding the physiological and molecular mechanisms involved in cross‐stresses tolerance is crucial for breeding strategies and achieving multiple stress resistance and eventually more sustainable agriculture. The objective of this study was to investigate the effect of a mild N‐deficiency on drought stress tolerance of tomato plants (Solanum lycopersicum L., cv. Moneymaker). Various morphological and physiological parameters such as dry biomass, root length, water potential, SPAD values, stomatal conductance, and compatible solutes accumulation (proline and sugar) were analyzed. Moreover, the expression of ROS scavenging marker genes, cytosolic ASCORBATE PEROXIDASES (cAPX1, cAPX2, and cAPX3), were investigated. Our results showed that a former mild N‐deficiency (2 mM NO3−) enhances plant adaptive response to drought stress (4 days) when compared to the plants treated with adequate N (5 mM NO3−). The improved adaptive response was reflected in higher aboveground biomass, longer root, increased specific leaf weight, enhanced stomatal conductance (without reducing water content), and higher leaf sugar content. Moreover, the APX1 gene showed a higher expression level compared to control under N‐deficiency and in combination with drought in the leaf, after a one‐week recovery period. Our finding highlights a potentially positive link between a former mild N‐deficiency and subsequent drought stress response in tomato. Combining the morphological and physiological response with underlying gene regulatory networks under consecutive stress, provide a powerful tool for improving multiple stress resistance in tomato which can be further transferred to other economically important crops.
Forests are key biomes linked to biogeochemical cycles, important species reservoirs and major ecosystem services providers. The observed global climate change in the 20th century has the potential to deeply affect the conservation, functioning and structure of these ecosystems. Expressed as rising average temperatures due to the increase in atmospheric concentration of greenhouse gases such as carbon dioxide, nitrate oxide and methane, pollutants which are mostly product of burning fuel for industrial activities. These long-term changes will be heterogeneous in time and space throughout the globe. For northeastern Germany, predictions indicate that summer temperature and winter precipitation will be at a constant rise, whereas summer precipitation is expected to decrease, conditions will increase the risk of drought conditions. The changes in long-term means will be accompanied by increased frequency of weather extremes. The overall effect of climate change, both its long- and short-term components and their interaction with forest growth is uncertain. Tree
species in the temperate forest are highly adapted to seasonal growth, active in late-spring and summer when temperature thresholds activate primary and secondary growth as well as leaf development, given sufficient water availability. During winter, they become dormant as an strategy to decrease damage by freezing temperatures. These adaptations ultimately determine species distributions as they occur along climate gradients within their ecological
optima. Thus climate change can have a significant effect on species distribution ranges and more locally it can change species abundances. Trees being sessile organisms, possess limited dispersal capacities and rely on their adaptation potential, both genetically through selection over generations and through phenotypic plasticity (e.g. the capacity of adapting to changing conditions within a lifetime).
Tree growth can be explored by dendrochronological methods, that is, by analyzing traits of annual xylem bands as produced by the vascular cambium. These traits are width, wood anatomical properties (e.g. cell wall thickness, lumen diameter), and isotopic composition.
Tree-rings are integrators of environmental conditions and indicators of vitality and productivity of trees and forests. Studying these traits allows to understand the effect of climate on growth and physiological function over decadal to centennial scales in the past and by it inform about future growth performance. However, environmental information is not trivially extracted from tree-rings. Environmental signals in tree-rings are often the result of
complex interactions of lagged meteorological conditions and tree-scale characteristics such as size, canopy status (i.e. social status), competition and stand density, among other factors. For this reason the monitoring of secondary growth as it unfolds, for example through dendrometer monitoring (i.e. record of the stem-radial variations at intra-annual temporal scales) and repeated sampling for the study of xylogenesis, is of major importance to understand climate-growth relationships and bridge the gap between dendroecological analysis atdifferent ecological scales (from single trees to stands to populations). Therefore this thesis contains contributions a) to the understanding of long-term climate shifts and its effect on tree growth for species in the Central European temperate forests through dendrochronological assessments and contributions b) to understanding intra-annual growth dynamics and
its relationship to meteorological conditions through the analysis of monitoring records. In the retrospective analysis chapters (I-III), first an assessment was performed of the climate-growth relationships of important species of these region which indicated that deciduous species’ growth (Fagus sylvatica, Quercus robur and Q. petreae) was influenced mostly by summer water availability. For Pinus sylvestris was late spring temperature. Negative correlations between winter temperatures and growth indices of deciduous species increased over the last decades, possibly linked to less snow cover of the soil leading to root damage causing growth reductions. Scots pine presented the opposite, as positive correlations with winter temperatures became more frequent, indicating that this species’ growth rates might
benefit from an elongation of the vegetation period. Afterwards the effect of stand characteristics in the climate response was explored. The climate signal of solitary oak trees growing in northeastern Germany was compared to oaks in closed stands. Solitary trees
expressed higher growth rates and drought signals, which endanger its conservation as dry conditions are expected to increase in the region. As in the temperate forest crowding effects are variable throughout a tree’s lifetime, as well as other limiting factors (e.g. climate), we subsequently developed a methodology based on analysis of individual tree-ring series rather than chronologies (site means) to disentangle these effects on heterogeneous samples and quantify them. By sampling all present crown classes in a site near Rostock (Germany), we found beech was mostly affected by water availability in the previous summer
and this effect was well represented throughout the population. For oak the main climatic driver of growth was previous October temperature with a low representation throughout the obtained sample. For beech, the main trait governing the variability around the response to the main climate driver of growth was cambial age, and for oak was crown-projection/size. On the prospective analysis chapters (IV-VI), monitoring datasets from the years 2013-2019 were used for the analysis of meteorological forcing of dendrometer series, the effect of a multi-year drought event and for the development of a method to combine continuous dendrometer records with discrete histological observations from xylogenesis analysis. The analysis of meteorological forcing on stem-radial variations indicated all observed species (beech, oak, hornbeam in this case) respond similarly to atmospheric water content whereas
the growth phenology displayed contrasting species differences. These findings indicate high-frequency variations in stem dynamics are similar between species as it reflects transpiration and water transport in the stem, whereas the timing of growth reflects life strategies and
wood anatomical adaptations. Next we evaluated the effect of the consecutive drought years 2018-2019 using dendrometer data (beech, oak, hornbeam and sycamore maple). The increment levels after the onset of drought in 2018 were not reduced for the observed individuals, whereas in 2019 all species showed decreased growth levels, particularly beech. Most likely the water moisture reservoirs were adequately filled in winter and spring before summer 2018, which lead to increased buffer capacity to withstand the harsh conditions for radial growth. However in winter, and the spring before the summer of 2019, there was not sufficient precipitation which lead to less resistance to the second bought of the drought event.
This illustrates the complex lagged meteorological effect on radial growth, which is easily obscured in retrospective dendroecological analysis and emphasizes the pivotal role of soil moisture and soil water storage in tree-growth analysis. As a final contribution, while recognizing the importance of prospective growth monitoring, we developed a software tool to visualize and combine dendrometer stem-radial variations with images of histological events, such as those obtained by microcores for xylogenesis analysis. Growth signals in dendrometers are often of smaller magnitude than variations related to stem-water dynamics. By comparing them with histological images of wood-formation it is possible to accurately assign growth phases to dendrometer series and optimize their assessment. The advancement in methodological approaches to study intra-annual tree growth data is of major importance in the context of permanent ecological monitoring plots and its role in the assessment of the consequences of climate change on forest growth and conservation.
Overall the findings of this thesis indicate that climate change impacts in the temperate forest of Central Europe will be and have been varied depending on the species considered with stand, site and tree-level conditions strongly modulating its consequences and even direction. Deciduous species, particularly beech, will be at risk due to decreased water availability during summer for which beech shows a high sensitivity. While oak seems to
be less prone to drought related growth reductions and it is plausible to consider changes in dominance towards drier sites, it is still at risk if vulnerability thresholds are crossed. Scots pine appears to be favored by the increased temperatures during late winter, although these are naturally found on poor sites or sites either too dry or too wet for other dominant deciduous species to establish. Nevertheless, Scots pine has been planted on a variety of site conditions and especially in northeastern Germany is among the most widespread and economically important forest trees. Furthermore, the individual variability we have found in climate responses indicates that heterogeneous stands contain resilient sub-populations that
could guarantee survivorship of the species after stark changes in climate means. However, it appears that strong enough stressors such as hotter droughts can trigger wide ecosystem changes with more efficiency than shifts in climate means. Due to this intra-annual growth
monitoring is particularly relevant to foretell ecosystem changes and to understand the complex relationships found in climate-growth analysis performed in dendroecological studies, as it permits to mechanistically understand how conditions outside the tree-ring formation
period affects wood formation.
Global change, amongst others characterized by increasing temperatures, altered precipitation patterns, an increase of extreme climatic events and continued atmospheric depositions of pollutants, is expected to severely impact forest ecosystems worldwide. The complex interplay between different factors acting upon tree growth, combined with regional patterns in climatic change calls for a region specific evaluation of the possible consequences on forest ecosystems. For northeastern Germany regional climate models identify a rise in temperatures and a change in precipitation patterns. Drier summers and wetter winters together with an increase in extreme weather events are seen as the most pronounced changes that will occur during the 21st century. In this thesis I analysed past growth rates and climate-growth relationships in different stands of beech (Fagus sylvatica L.) and oak (Quercus robur L.) along a gradient of decreasing precipitation in a space for time approach. Special attention was paid to the influence of summer drought, soil waterlogging and the importance of site conditions in modulating the reactions to these climatic stressors. Departing from these retrospective analyses, future growth trends are modelled for beech, oak and Scots pine (Pinus sylvestris L.), based on projections of a regional climate model until the year 2100. Furthermore, I studied the influence of sudden and extreme shifts in hydrological conditions on the growth of oaks in a drained peatland that was subject to catastrophic rewetting. All analyses of this thesis are based on ring-width and wood anatomical features applying a variety of dendrochronological methods. The gradient approach revealed similar climate-growth relationships for beech and oak on drought exposed, sandy sites, where water availability during early summer was the main growth-limiting factor for both species. Decreasing precipitation rates towards the East are associated with higher drought susceptibility, especially for beech. As a result, competitive superiority of beech over oak decreases. In a drier future the competitive balance between the two species may shift (rank reversal). During the past decades beech has shown larger interannual growth variability and a higher number of growth depressions. These changes might indicate that increasing temperatures and climatic variability are already affecting its growth patterns and climate sensitivity. This is in line with the prospective modelling approach. According to our models, growth trends will turn negative for beech and oak towards the end of the 21st century, with beech showing the highest growth reduction (23% compared to the reference period 1971-2000). For pine, modelled growth rates show only minor changes. Whereas beech and oak shared a high common signal on the dry sites, the two species differed in high frequency ring patterns on the wet sites. On poorly drained, loamy soils beech, with its superficial root system, suffered from summer droughts. In contrast, on these sites ring-width of pedunculate oak was not correlated to summer moisture conditions resulting in differing interannual ring patterns between dry and wet sites. Wet periods with high soil water saturation did not have a negative influence on the growth of either species. Such a lack of response is not surprising for oak, which is generally known as rather tolerant to soil waterlogging, but it indicates an unexpectedly high tolerance of beech to stagnating wetness. Using the natural laboratory of an oak forest that suffered a catastrophic flooding I could show that slower grown trees that had likely been suppressed displayed a higher adaptive capacity compared with bigger, dominant trees. Many of the previously dominant individuals died within 18 years after the event. Trees that survived the groundwater rise displayed a typical ring pattern: growth was suppressed for a few years, but afterwards recovered and even surpassed previous growth rates, most likely as a result of competition release. The sudden hydrological change left a clear imprint in ring patterns and wood anatomical features in both the dying and the surviving trees. This differentiated imprint may be helpful for a better interpretation of growth patterns found in subfossil bog oaks, an important climate proxy of the Holocene. The insights gained from this thesis support existing concerns about drought induced growth decline for oak, but especially for beech. Changes in precipitation patterns might lead to wetter conditions during winter, but these will likely have only little effect on growth. Both s show rather high resilience to stagnating wetness. More likely, it are extreme events like prolonged droughts or heavy rainfalls that might breach thresholds in the ability of the two species to cope with too much or too little water. Such extreme events thus pose a strong risk to the future growth performance of both oak and beech.
Forests are and have been of major importance to cover a variety of societal needs. Today the demands on forests are ever increasing with sequestering carbon and balancing the climate, to name only a few. To cover those requirements forests need vital, productive, and sustainable. A difficult concept as such as the understanding of a healthy forest varies greatly. Nevertheless, forests still have to produce a sufficient amount of yield while threatened by changing climate conditions. These are predicted to bring extended and more intense drought periods as well as a higher frequency of storms and the promotion of secondary disturbances like insects calamities to also rise. In this complex situation of high and versatile demand the focus is on the allocation of the “right” forest. Forest management is requested to balance the needs of humans against those of wildlife against those of the trees themselves. To gain the respective knowledge on species responses and provenance growth, now and in the future research gaps need to be closed. All factors influencing tree growth and therefore ultimately yield need to be understood and special focus needs to be on the interactions within the forest ecosystem. One of the parameters in understanding aggregated tree growth is the dynamic of growth. This can be visualised by dendroecological methods, providing a picture of growth within the individual years. Growth dynamics are dependent on multiple factors, some, like soil being preconditioning and other like climate causing short-term responses. In this thesis I focus on the influence of climate on annual tree growth using a new approach of daily climate data to calculate climate-growth correlations. This method has the advantage of representing tree processes better than the former approach of using monthly means. Furthermore the program enables the user to feed climate scenarios and therefore estimate future growth. To gather information on species as well as provenance differences to provide advice to foresters I used different trials in Britain and Germany. On the British site different oak species were planted while the German sites are stocked with various spruce provenances. For the latter we additionally used stable carbon isotope analysis to calculate intrinsic water use efficiency. The climate-growth correlations revealed differences between the oak species with a generally higher linkage to precipitation than temperature. While the differences are clear, the question of thresholds and the role of extreme events became apparent in this work. VII Abstract Assessing the impact of extreme events using dendrometer data revealed little differences in the response to short term events of the three investigated species, oak, beech, and pine. We were able to pick up stimulus-response-relationships and as a novel result no species-specific responses were found when focusing on such a small time frame. The provenance trials offered the opportunity to investigate the potential of the use of daily climate data more closely. The two contrasting sites planted with six spruce provenances each gave an insight on the adaptive potential of provenances as well as an indication on the response times. Depending on the proceeding environmental and the local climate conditions decisions have to be made on the species or provenance selection. This thesis provides a method as well as insight on the behaviour of the important European species beech, oak, pine, and spruce. It, however, highlights the limitations such methods have for large scale estimates. While general trends on the response to specific soil factors can be used, the climatic responses, be it thresholds or climate-growth correlations can only be seen within the ecological context of their sampling region.
Direct and Indirect Effects of Environmental Limitations on White Spruce Xylem Anatomy at Treeline
(2021)
Treeline ecosystems are of great scientific interest to study the effects of limiting environmental conditions on tree growth. However, tree growth is multidimensional, with complex interactions between height and radial growth. In this study, we aimed to disentangle effects of height and climate on xylem anatomy of white spruce [Picea glauca (Moench) Voss] at three treeline sites in Alaska; i.e., one warm and drought-limited, and two cold, temperature-limited. To analyze general growth differences between trees from different sites, we used data on annual ring width, diameter at breast height (DBH), and tree height. A representative subset of the samples was used to investigate xylem anatomical traits. We then used linear mixed-effects models to estimate the effects of height and climatic variables on our study traits. Our study showed that xylem anatomical traits in white spruce can be directly and indirectly controlled by environmental conditions: hydraulic-related traits seem to be mainly influenced by tree height, especially in the earlywood. Thus, they are indirectly driven by environmental conditions, through the environment’s effects on tree height. Traits related to mechanical support show a direct response to environmental conditions, mainly temperature, especially in the latewood. These results highlight the importance of assessing tree growth in a multidimensional way by considering both direct and indirect effects of environmental forcing to better understand the complexity of tree growth responses to the environment.
Diversified livelihoods combining farming, livestock keeping and non-farm income arecharacteristic of many rural households worldwide. For the Central Asian and Caucasian region,livestock keeping is especially important in terms of land use and socio-cultural heritage. We contributeto the literature with data from the under-researched Caucasus region and investigate: (i) the extent ofdiversification in smallholder households; (ii) the role of livestock keeping in diversification; (iii) theinfluence of household-specific and location-specific variables and diversification on householdincome. Based on a dataset of 303 households, we calculate contribution margins for the mainagricultural activities, household income, and diversification indices and analyze the influence ofdiversification, asset and location variables on household income with a regression model. Householdincome is generally diversified and a combination of four income sources (crops, livestock, poultry/beesand social benefits) was the most frequent. The econometric analysis shows that higher householdincomes are positively correlated with higher household land and livestock assets, the presence ofnon-farm work and social benefit income sources and with an increasing specialization as measuredby the diversification index. For enhancing rural household incomes and slowing down rural-urbanmigration, the development of non-farm job opportunities is recommended.
Tree growth in northern and upper treeline ecotones of the circumpolar boreal forest is
generally limited by temperature, i.e., trees grow generally more under warm, and less under
cold climatic conditions. Based on the assumption that this relationship between tree growth
and climate is linear and stable through time, dendroclimatologists use tree rings as natural
archives to reconstruct past temperature conditions. Such tree-ring based reconstructions,
together with other natural archives (e.g., ice cores and pollen), constitute our understanding of
past climatic conditions that reach beyond modern instrumental records.
However, a steadily increasing amount of studies reports a recent reduction or loss of the
summer temperature signal for several species and sites of the boreal forest. Such a reduction
of temperature sensitivity results in temporally unstable climate-tree growth relationships,
which challenges the work of dendroclimatologists by potentially leading to miscalibrations of
past climatic conditions. On the upside, this shift in the trees’ climate sensitivity might point to
a shift in tree growth-limiting factors and thus serve as an early indicator of climate change
impacts. There is evidence that this recent reduction in temperature sensitivity might be caused
by the observed strong temperature increase at high latitudes, and thus temperature-induced
drought stress. Other potential drivers and amplifiers of this phenomenon are differing microsite
conditions (dry vs. wet soils) and factors inherent to trees, like genetic properties or age
effects.
In this PhD thesis, I systematically assessed the effects of frequently discussed drivers of
unstable climate-tree growth relationships (climate change, micro-site effects, genetical
predisposition) on two representative species of the boreal forest, white spruce in North
America and Scots pine in Eurasia, across various temporal and spatial scales. I used classical
(tree-ring width) and more novel (wood density, quantitative wood anatomy)
dendrochronological proxies to unravel the effects from annual to sub-monthly resolution.
More precisely, in chapter I, white spruce clones were compared to non-clones at two treeline
sites in Alaska to test whether their growth patterns differ, and whether white spruce clones are
generally suitable for dendroclimatic assessments. Clonal reproduction is frequent at treeline
due to harsh conditions, but might lead to competition among individuals due to the close
proximity among each other, which in turn might obscure their climatic signal. Second, I tested
the effect of warmer and drier climatic conditions on the summer temperature signal of Scots
pine in Eurasia (chapter II) and on the growing season moisture signal of white spruce in North
America (chapter III), respectively. Temperature-induced drought stress is expected to be the
most important driver of unstable climate-growth relationships in the boreal forest. I included
several sites across latitudinal (50-150 km) and longitudinal (1,000-2,200 km) gradients to
cover large parts of the species’ distribution ranges. Since Scots pine covers a wide range of
ecological habitats, I additionally tested the effect of dry and wet micro-site conditions on the
summer temperature signal of Scots pine in chapter II. Finally, in chapter IV, a systematic
literature review was carried out in order to investigate the distribution of unstable climategrowth
relationships in global tree-ring studies, and the usage of such series in climate
reconstructions. Furthermore, the scientific impact of these potentially inaccurate climate
reconstructions was assessed.
In this PhD project, warmer and drier climatic conditions led to temporally unstable climate
signals in both Scots pine (chapter II) and white spruce (chapter III), as expected. Unstable
climate-growth relationships were found for all tested tree-ring proxies and at all sites in North
America, and at most sites in Eurasia. Micro-site effects (chapter II) and clonal growth
(chapter I) had no significant effect on the climate sensitivity and high-frequency variability
of the tested species, but affected absolute growth. The review (chapter IV) revealed that the
phenomenon of unstable climate-growth relationships is globally widespread, and occurs
independent of tree species, geographic location, and tree-ring and climate proxies. While
reconstructions inferred from these unstable relationships are frequent and respective papers
have a high impact, the tree-ring community seems to increasingly recognize the challenge of
unstable climate-growth relationships.
With these findings, this PhD project helped to shed more light on the frequency, underlying
drivers, and the impact of unstable climate-growth relationships in boreal forest trees, as well
as underlying reaction processes in trees. Above all, this PhD project suggests that the loss of
climate sensitivity is caused by a change of growth limiting factors: temperature limitation
seems to be suspended in warmer and drier years for Scots pine in Eurasia, and moisture
limitation first arises under warm/dry conditions for white spruce in North America. Due to
plastic growth responses in trees, the general assumption in dendroclimatology – that climategrowth
relationships are stable through time – seems to be incompatible with the principle of
limiting factors (one factors is always most growth limiting).
To improve the validity of future climate reconstructions, statistical approaches considering
synchronously or changing climatic limiting factors need to be promoted, along with attempts
to select the best responding trees from a dataset. Furthermore, a better understanding of nonclimatic
factors potentially affecting tree growth (e.g., age, disturbance, soil parameters) is
needed. A growth reduction of mature and dominant white spruce trees sampled in this PhD
project seems likely under future warming conditions, with series of wood cells being valuable
early indicators of climate change effects in white spruce. However, inferences cannot be
extended to the entire stand due to the applied sample design. Projected climate warming will
probably lead to a further reduction of the summer temperature signal in trees of the northern
boreal forest, while wider consequences for forest growth and productivity are unclear.
Duckweeds include the world's smallest and fastest growing flowering plants that have the capacity to produce huge biomass with a broad range of potential applications like production of feed and food, biofuel and biogas. In order to achieve optimal and sustainable commercial system, it is necessary that suitable species and clones of duckweeds be identified and selected based on appropriate strategies. However, a high degree of reduction in their structural complexity poses serious problems in identification of closely related species of duckweeds, on a morphological basis. Use of molecular taxonomic tools is the present solution. The state of the art of molecular taxonomy of all the five genera of duckweeds (Spirodela, Landoltia, Lemna, Wolffiella, and Wolffia) is based mainly on the techniques of fingerprinting by amplified fragment length polymorphism (AFLP) and barcoding using sequences of plastidic DNA fragments. After more than 15 years of molecular taxonomic investigations, a certain viewpoint is now available demonstrating all five genera to be monophyletic. Also, the phenetic analyses had made huge progress in delineating the currently defined 36 species of duckweeds, although, all species cannot yet be defined with confidence. Wolffiella has turned out to be the most complicated genus as only 6 to 7 species out of the 10 can be reliably delineated. Further progress in the phylogenetic and phenetic analyses requires more advanced methods like next generation and/or whole genome sequencing. First results using the method genotyping-by-sequencing in the genus Lemna (in combination with metabolomic profiling by matrix-assisted laser desorption ionization time-of-flight mass-spectrometry (MALDI-TOF-MS) as well as AFLP and barcoding by plastidic sequences) are more promising: The species Lemna valdiviana and Lemna yungensis were united to one species, Lemna valdiviana. This reduced the total number of Lemnaceae species to 36.
Duckweeds (Lemnaceae) are the smallest and fastest-growing angiosperms. This feature, together with high starch production and good nutritional properties, makes them suitable for several applications, including wastewater treatment, bioenergy production, or feed and food supplement. Due to their reduced morphology and great similarity between diverse species, taxonomic identification of duckweeds is a challenging issue even for experts. Among molecular genotyping methods, DNA barcoding is the most useful tool for species identification without a need for cluster analysis. The combination of two plastid barcoding loci is now considered the gold standard for duckweed classification. However, not all species can be defined with confidence by these markers, and a fast identification method able to solve doubtful cases is missing. Here we show the potential of tubulin-based polymorphism (TBP), a molecular marker based on the intron length polymorphisms of β-tubulin loci, in the genomic profiling of the genera Spirodela, Landoltia, and Lemna. Ninety-four clones were analyzed, including at least two representatives of each species of the three genera, with a special focus on the very heterogeneous species Lemna minor. We showed that a single PCR amplification with universal primers, followed by agarose gel analysis, was able to provide distinctive fingerprinting profiles for 10 out of 15 species. Cluster analysis of capillary electrophoresis–TBP data provided good separation for the remaining species, although the relationship between L. minor and Lemna japonica was not fully resolved. However, an accurate comparison of TBP profiles provided evidence for the unexpected existence of intraspecific hybrids between Lemna turionifera and L. minor, as further confirmed by amplified fragment length polymorphism and sequence analysis of a specific β-tubulin locus. Such hybrids could possibly correspond to L. japonica, as originally suggested by E. Landolt. The discovery of interspecific hybrids opens a new perspective to understand the speciation mechanisms in the family of duckweeds.
Carbon dioxide (CO2) is one of the most important factors of the Earth’s carbon cycle. Peatlands are well-known to be a long term sink for atmospheric carbon dioxide. Under changing environmental conditions, the carbon balance and hence the CO2 fluxes can be significantly changed, and peatlands may even become a significant atmospheric carbon source. To be able to predict the changes in climatic conditions and their effects on ecosystems, it is important to understand the contemporary CO2 exchange of the ecosystems. Many studies on peatland CO2 fluxes have been conducted in the boreal zone of North America and Scandinavia. Still little scientific evidence is available from peatland ecosystems of boreal Russia. This dissertation presents the detailed investigation of CO2 dynamics and the relevant processes and environmental factors from the boreal peatland site Ust-Pojeg (61°56'N, 50°13'E) in Komi Republic, northwest Russia. On the small spatial scale (microform), the investigated peatland was characterised by high variability in vegetation composition and coverage as well as in water table level which resulted in large variability in CO2 fluxes not only between the microform types but also within one microform type. The cumulative flux over the investigation period for the different microforms ranged from strong CO2 sources to CO2 sinks. An area-weighted estimate for the entire peatland showed that it was a CO2 source for the investigation period, which was characterised by average conditions in terms of precipitation and temperature. The CO2 fluxes were measured at different scales: by the closed chamber method at the microform scale and by the eddy covariance technique at the ecosystem scale. Three different upscaling methods were used to compare the fluxes. Irrespective of the upscaling methods, the discrepancies between the estimates based on the upscaled chamber measurements and estimates based on measurements by the eddy covariance technique were high. The high spatial heterogeneity of the vegetation and the water table level and thus of the CO2 fluxes were recognised as reasons for high potential errors when upscaling CO2 fluxes from the microform to the ecosystem level. Large discrepancies were also observed in comparison between measured CO2 fluxes and CO2 estimates based on the mechanistic ecosystem model LPJ-GUESS. Insufficient model forcing may have led to errors in the timing of the onset and the end of the growing season, and the modelled vegetation did not always reproduce the observed vegetation. These two factors may have led to the discrepancies in the model-measurement comparison. Although the closed chamber technique is widely used for measurements of CO2 fluxes between ecosystems and the atmosphere, the errors which might occur during the measurement itself or which are associated with the used measurement devices as well as the flux calculation from chamber-based CO2 concentration data are still under discussion. The study showed that the CO2 fluxes measured by the closed chamber method can be overestimated during low-turbulence nighttime conditions and can be seriously biased by inappropriate application of linear regression for the flux calculation. The methodological studies were conducted at the boreal peatland Salmisuo in eastern Finland (62°46'N, 30°58'E). The methods developed in this dissertation could contribute significantly to improved CO2 flux estimates. VI
Ecological Impacts and Phenotypic Plasticity of a Global Invasive Cactus, Opuntia ficus-indica
(2023)
Biological invasions by non-native species pose one of the major threats to biodiversity, the way ecosystems function, and the well-being of humans. These invasions can occur through various means, including accidental or intentional introductions by humans, natural dispersal, and climate change. Non-native species can harm the native species and ecosystems, by homogenizing plant communities, competing for resources, changing how the ecosystem operates, and eventually causing native species to go extinct. Even though not all non-native species become invasive, changes in climate and ecosystems can cause the successful establishment and spread of non-native species. Despite the advancements in our understanding of biological invasions in recent years, research has been biased towards temperate regions, whereas arid and semi-arid regions that are highly impacted by climate change are underrepresented. Thus, particularly focusing on the impacts of biological invasions in subtropical arid and semi-arid regions, the goal of this PhD project was to explore the effects of an invasive cactus on the local native communities and investigate the mechanisms of its successful invasion. Certain species are found to take advantage of the ever-drying climates in the arid/ semi-arid regions of the world. Opuntia ficus-indica, native to Mexico, is an exceptionally successful drought-tolerant invasive cactus that successfully grows in these regions. O. ficus-indica, a most widespread invasive cactus, is considered an ecosystem engineer as it modifies the habitats of indigenous plant species and dependent animals. This project aimed to identify the ecological impacts of O. ficus-indica in the highlands of Eritrea, the competitive potential of O. ficus-indica and the plastic changes that enabled its spread and invasion (Chapters I-III). For this purpose, field observations and common garden experiments were carried out throughout the project.
We investigated the effects of Opuntia ficus-indica on the spatial diversity of native plant communities (Chapter I), its competitive ability against native species (Chapter II) and the phenotypic plasticity of O. ficus-indica (Chapter III). To investigate the main ecological effects of O. ficus-indica on the native community, field data was collected from the highlands of Eritrea and comparisons were made between O. ficus-indica invaded and noninvaded areas (Chapter I). The study aimed to understand the effects of O. ficus-indica by examining species composition, richness, and diversity across vegetation layers and revealed that O. ficus-indica homogenises the species composition of the native ecosystem. This provides evidence that the presence of O. ficus-indica reduces landscape-level heterogeneity or spatial diversity. However, O. ficus-indica did not influence the species richness and diversity of the local communities. The mechanisms of the successful homogenisation of the local communities by O. ficus-indica were attributed to the potential competitive abilities of O. ficus-indica against the native species, and the plastic and adaptive traits it developed in the non-native ranges. The first assumption was tested by setting up a common garden competition experiment between two native Eritrean species, Ricinus communis and Solanum marginatum (Chapter II). The experiment used two water availability treatments, wet and dry, and categorized plants into intraspecific (native or invasive only) and interspecific (native and invasive) competition. The study evaluated the impacts by comparing the growth of O. ficus-indica alone to the growth alongside native species which revealed the weak competitive potential of O. ficus-indica. However, O. ficus-indica was observed to outgrow the native species in several folds which can be attributed to its successful invasion. The second assumption of the successful spread of O. ficus-indica was attributed to the phenotypic plastic traits adapted by O. ficus-indica in the non-native ranges (Chapter III). The phenotypic plasticity of O. ficus-indica was assessed by exposing it to water stress across dry and wet environments. The species were cultivated from a diverse set of 12 populations, encompassing its native range in Mexico with three cultivars and nonnative ranges in Africa (Algeria, Eritrea, Ethiopia), the island of Madeira off the coast of Africa, and in Europe, Italy with two cultivars and in Portugal from three sites. In Mexico and Italy, we collected various cultivars to ensure a wide representation of genotypes. We found that the species originating from the native range of O. ficus-indica exhibited lower plasticity to conditions of elevated water availability. Furthermore, a trial gradient experiment on O. ficus-indica was conducted to determine the appropriate watering levels for the species and the experiment revealed not only the species' capacity to endure a lack of water for nine months but also its ability to withstand prolonged waterlogged conditions.
This thesis illustrates the fact that invasive species are a major threat to biodiversity and ecosystem functioning worldwide, especially in rarely studied regions with dry climates and limited resources. How can invasive plants spread and cause negative impacts on native ecosystems (Chapter I), despite their weak competitive abilities (Chapter II)? This thesis explored these questions by examining the case of O. ficus-indica, an invasive species in arid/ semi-arid climates (Chapter I). It showed that O. ficus-indica has a high growth potential that allows it to overcome resource limitations, that its growth is not affected by competition from native species (Chapter II), and that it exhibits adaptive plasticity that enhances its invasion success in different environments (Chapter III). This thesis revealed the complex mechanisms and consequences of biological invasions in dry climates and contributes to the understanding of invasive species. It also suggests that more research is needed in understudied regions to assess the impacts of O. ficus-indica or invasive species in general on native biodiversity and ecosystem services and to identify the factors that influence the competitive and adaptive potentials.
Forests are ecologically important ecosystems, for example, they absorb CO2 from the
atmosphere, mitigate climate change, and constitute habitats for the majority of terrestrial
flora and fauna. Currently, due to increasing human pressure, forest ecosystems are
increasingly subjected to changing environmental conditions, which may alter forest growth
to varying degrees. However, how exactly different tree species will respond to climate
change remains uncertain and requires further comprehensive studies performed at different
spatial scales and using various tree-ring parameters.
This dissertation aims to advance the knowledge about tree-ring densitometry and
tree responses to climate variability and extremes at different spatial scales, using various
tree species. More specifically, the following aims are pursued: (i) to obtain and compare
wood density data using different techniques, and to assess variability among laboratories
(Chapter I). (ii) To investigate microsite effects on local and regional Scots pine (Pinus
sylvestris L.) responses to climate variability (Chapter II) and extremes (Chapter III),
using ring width (RW) and latewood blue intensity (LBI) parameters. (iii) To give a general
site- and regional-scales overview of Scots pine, pedunculate oak (Quercus robur L.), and
European beach (Fagus sylvatica L.) RW responses to climate variability (Chapter IV). (iv)
To discuss the challenges which may result from compiling tree ring records from different
(micro)sites into large-scale networks. The study area comprises nine coastal dune sites, each
represented by two contrasting microsites: dune ridge and bottom (Chapters II and III), and
310 different sites within the south Baltic Sea lowlands (Chapter IV).
The dissertation confirms that sample processing and wood density measuring are
very important steps, which, if not performed carefully, may result in biases in growth trends,
climate-growth responses, and climate reconstructions. The performed experiment proved
that the mean levels of different wood density-related parameters are never comparable due
to different measurement resolutions between various techniques and laboratories. Further,
the study revealed substantial biases using data measured from rings of varying width due
to resolution issues, where resolution itself and wood density are lowered for narrow rings
compared to wide rings (Chapter I).
The (micro)site-specific investigation showed that, depending on the species,
different climate variables (temperature, precipitation, or drought) constitute important
factors driving tree growth across investigated locations (Chapters II and IV). However,
there is evidence that the strength and/or direction of climate-growth responses differ(s)
between microsite types (Chapter II) and across sites (Chapter IV). Moreover, climategrowth
responses are non-stationary over time regardless of the tree species and tree-ring
parameter used in the analysis (Chapters II and IV). There are also differences in RW and
LBI responses to extreme events at dune ridge and bottom microsites (Chapter III).
The regional-scale investigations revealed that climate-growth responses (strength
and non-stationarity) are quite similar to those observed at the local scale. However,
compiling RW or LBI measurements into regional networks to study tree responses to
extreme events led to weakened signals (Chapter III).
The findings presented in Chapters II and IV suggest that the strength, direction,
and non-stationary responses are very likely caused by several climatic and non-climatic
factors. The mild climate in the south Baltic Sea region presumably does not constitute a
leading limiting growth factor, especially for Scots pine, whose distribution extends from
southern to northern Europe. Thus, the observed climate-growth responses are usually of
weak to moderate strength. In contrast, for other species reaching their distribution limit at
the Baltic coast, the climatic signal can be very strong. However, the observed findings also
result from the effects of microsite conditions, and potentially other factors (e.g.,
management, stand dynamic), which all together alter the physiological response of the tree
at a local scale. Although climate at the south Baltic Sea coast is mild, extreme climate events
may occur and affect tree growth. As demonstrated (Chapter III), extreme climate events
affected tree growth across dune sites, however, to varying degrees. The prominent
differences in tree responses to extreme climate events were significant at the local scale but
averaged out at the regional scale. This is very likely associated with observed microsite
differences, where each microsite experiences different drivers and dynamics of extreme
growth reductions.
This dissertation helped to demonstrate that integrating local tree-ring records into
regional networks involves a series of challenges, which arise at different stages of research.
In fact, not all possible challenges have been discussed in this dissertation. However, it can
be summarized that several steps performed first at the local scale are very important for the
quality and certainty of climate-growth responses, tracking tree recovery after extreme
events, and potential climate reconstructions at the larger scale. Among them, identification
of microsite conditions, sample preparation, and measurement, examination of growth
patterns and trends, and identification of a common limiting growth factor are very
important. Otherwise, the compilation of various tree-ring data into a single dataset could
lead to over- or underestimation of the results and biased interpretations.
Myxomycetes are protists belonging to the super-group Amoebozoa. The traditional taxonomic system, which is now largely outdated by molecular studies, recognizes five orders: Liceales, Trichiales, Physarales, Stemonitales and Echinosteliales. Molecular phylogenies revealed two basal clades: Physarales and Stemonitales (the so-called dark-spored myxomycetes) are the first; the other above-mentioned orders form the second (the bright-spored myxomycetes). However, except for Echinosteliales none of the traditional orders appears to be monophyletic in the traditionally used delimitation. The dark-spored myxomycetes encompass the majority of the described morphospecies. Due to the high genetic divergence in DNA sequences between the bright- and dark-spored myxomycetes, only the latter are considered in this dissertation. Historically myxomycetes have been described as fungi, due to their macroscopically visible fructifications which, though considerably smaller, resemble those of fungi. These fruit bodies provide enough morphological traits to support a morphological species concept with currently ca. 1000 species described. Therefore diversity studies of myxomycetes have been conducted for over 200 years and a substantial body of data on ecology and distribution of these fructifications exist. From these studies myxomycetes are known to form often distinct communities across terrestrial ecosystems with highly specific habitat requirements, such as snowbanks (nivicolous), herbivore dung (coprophilous) or decaying wood (xylophilous). However knowledge on the myxamoebae – the trophic life stage of the myxomycetes – is very scarce. Only recent advances in molecular techniques such as direct species identification based on DNA sequences from environmental samples (ePCR), have made studies of myxamoebae (and other microbes) possible. From these first molecular based studies myxomycetes are currently estimated to account for between 5 to almost 50% of all soil amoebae, and have been shown to be present in a wide variety of soils. To fully take advantage of these new methods, a molecular DNA marker needs to be established as well as a reference sequence database. The usability of a DNA marker gene depends on its ability to separate species by a distinction between intra- and interspecific divergence between sequences of the same and related species, the so-called ‘barcoding gap’.
The first part of this thesis (article I and II) deals with the subject of establishing such a DNA marker and database, and in doing so touches upon the subject of ‘what is a myxomycetes species?’
A total of 1 200 specimens were compiled into a reference database (the largest database to date of dark-spored myxomycetes). The genetic distance from sequence-to-sequence was used to assess genetic clade structures within morphospecies and putative biospecies (sexually isolated linages) were identified. The result was an estimate of hidden diversity, exceeding that of described morphospecies by 99%. The optimum sequence similarity threshold for OTU-picking (genetic species differentiation, denoted Operational Taxonomic Unit) with the used SSU marker was identified as 99.1% similarity.
The second part of this thesis (article III and IV) presents ecological studies conducted with NGS (ePCR) in which the established threshold and database are applied and are demonstrated to provide reliable and novel insights into the soil myxamoebae community. It is investigated whether the occurrence of fruit bodies reflects the distribution of soil myxamoebae, and the research questions ‘do myxomycetes show broader realized niches as soil amoebae than as fructifications?’ and ‘are myxamoebae distributions correlated to potential prey organisms (fungi and bacteria)?’ are investigated.
In the ecological study presented in article III parallel metabarcoding of bacteria, fungi and dark-spored myxomycete was used for the first time in a joint approach to analyze the communities from an elevational transect in the northern limestone German Alps (48 soil samples). Illumina sequencing of the soil samples revealed 1.68 Mio sequences of a section of the rRNA gene, which were assigned to 578 operational taxonomic units (OTU) from myxomycetes. These show a high similarity (>98%) to 42 different morphospecies (the respective figures for bacteria and fungi were 2.16/5710/215 and 3.68/6133/260, respectively). Multivariate analyses were carried out to disentangle microbial interplay and to identify the main environmental parameters determining the distribution of myxamoebae and thus setting the boundaries for their ecological niches. Potential interactions between the three target organisms were analysed by integrating community composition and phylogenetic diversity with environmental parameters. We identified niche differentiation for all three communities (bacteria, fungi and myxamoebae) which was strongly driven by the vegetation. Bacteria and fungi displayed similar community responses, driven by symbiont species and plant substrate quality. Myxamoebae showed a more patchy distribution, though still clearly stratified among genera, which seemed to be a response to both structural properties of the habitat and specific bacterial taxa. In addition we find an altitudinal species turn-over for all three communities, most likely explained by adaptation to harsh environmental conditions. Finally a high number of myxomycetes OTUs (associated with the genus Lamproderma) not currently represented in our reference database were found, representing potentially novel species. This study is the first to report niche differentiation between the guild of nivicolous (“snowbank”) myxomycetes and thus fine-scale niche differentiation among a predatory soil protist; identifying both potential food preferences and antagonistic interactions with specific bacterial taxa.
Finally, the second ecological study (article IV) focuses on comparing the distribution of myxamoebae revealed by ePCR of soil samples with fructifications collected from the same area (714 specimens determined to 30 morphospecies, which form 70 unique ribotypes that can be assigned to 45 ribotype clusters using a 99.1% similarity threshold). The study found a strong coherency between the two inventories, though with species specific relative differences in abundance, which can in part be attributed to the visibility of the fructifications. In addition, a year to year comparison of fructification records gives support to the hypothesis that the abundance of fructifications depends strongly on the onset of snowfall in the previous autumn and the soil temperature regime throughout the winter.
Myxomycetes are fungus-like protists of the supergroup Amoebozoa found to be abundant in all terrestrial ecosystems. Mainly based on its macroscopically visible fruit bodies, our knowledge on ecology and diversity of myxomycetes is better than for most other protistean groups, but there is still a lacking knowledge about global diversity patterns since tropical regions, especially the old world tropics, are still understudied. In this thesis a combination of classical ecological analyses and modern molecular methods were used to expand the current knowledge on myxomycete diversity and biogeography in the Paleotropics. A number of surveys in the Philippine archipelago are conducted to provide and to add information about the distribution of myxomycetes in the Southeast Asian region. A combination of field collecting and ca. 2500 moist chamber cultures from four unexplored areas in the Philippines, namely, the Bicol Peninsula (746 records, 57 taxa), Puerto Galera (926 records, 42 taxa), Quezon National Park (205 records, 35 taxa), and Negros Province (193 records, 28 taxa), now brings the number of species recorded for Philippines to 150; with one record, Stemonaria fuscoides, noted as new for the Asian Paleotropics. Collecting localities that have more diverse plant communities showed as well higher species diversity of myxomycetes. In congruence with studies from the Neotropical forests, it seems also that anthropogenic disturbances and the type of forest structure affect the occurrence of myxomycetes for the Philippines. Another survey carried out in another paleotropical region, the highlands of Ethiopia, revealed a total of 151 records, with all 39 species found as new for the country. Three records of Diderma cf. miniatum with a strong bright red peridium and one record of Didymium cf. flexuosum with a conspicuous broad reticulation in the spore ornamentation were described and barcoded, since both may represent morphospecies new to science. A number of rarely recorded species, like Didymium saturnus, Metatrichia floripara, Perichaena areolata, and Physarina echinospora showed that resembling to its unique flora, the east African mountain ranges harbor a diverse and distinctive myxomycete assemblage. One incentive of this study was to compile a solid large dataset for the Paleotropical region that is comparable to data obtained from comprehensive studies performed in the Neotropical areas a decade ago. A total of eight surveys (with four comprehensive regional surveys, two from lowland and two from highland, for each region, the Neo- and the Paleotropics) were used, to compare the myxomycete assemblages of both regions. Each survey comes from a region with fairly homogenous vegetation, and includes specimens from both field and moist chamber cultures component. A statistical analysis of species accumulation curves revealed that only between 70 and 95% of all species to be expected have been found. Even for >1000 specimens per survey these figures seem hardly to increase with increasing collection effort, since a high proportion of species is always represented by a single or a few records only. Both ordination and cluster analysis suggests that geographical separation explains differences in species composition of the myxomycete assemblages much better than elevational differences. 5 The molecular component of this thesis is a phylogeographic study of the widely distributed tropical myxomycete Hemitrichia serpula. It is a morphologically distinct species with golden-yellow fructifications forming a reticulum. However, subtle variation in spore ornamentation points to cryptic speciation within this myxomycete. Using two independent molecular markers, 135 partial sequences of the small subunit (SSU) rRNA (a nuclear but extrachromosomal gene) and 30 partial sequences of the elongation factor 1 alpha gene (EF1A) (a nuclear gene), a study of 135 Hemitrichia serpula specimens collected worldwide revealed the existence of four clades that are likely to represent reproductively isolated biospecies, since each clade shows a unique combination of SSU and EF1A genotypes. A Mantel test with the partial SSU sequences indicated geographical differentiation, giving a correlation coefficient of 0.467 between the pairwise computed geographic and genetic distances, compared with the 95% confidence interval from 999 permutations (-0.013 to 0.021). Biogeographical analysis of the 40 SSU ribotypes showed clear intraspecific variation and geographic differentiation demonstrating a limited gene flow among the world population. We argue that the distribution of cryptic species in the different clade can be explained by ongoing, but still incomplete speciation. An event-based ancestral area reconstruction using the software S-DIVA employed in RASP showed that the probable origin of the ribotypes was a global dispersal event in the Neotropics. Additional species distribution models that were implemented for the three most prominent clades show different putative ranges. As such H. serpula supports the moderate endemicity hypothesis for protists. In summary, myxomycete assemblages in the Paleotropics (1) displayed a higher diversity than for Neotropical forests, (2) harbor unique taxa that differentiates those assemblages in spite of the expected similar macroecological all over the Tropics, (3) are affected by geographical barriers that likely causes speciation both at a morphospecies and biospecies level, and (4) follow the ubiquitous model in the sense that gene flow mediated by long-distance dispersal of spores is high enough that a species can fill out its entire putative range, but (5) the gene flow is not high enough to prevent variation in regional gene pools, which may lead to speciation and is better explained by the moderate endemicity model. Our data are still too limited to draw a comprehensive picture of the diversity of tropical myxomycetes, but the baseline information compiled with the aid of both classical ecology and molecular approaches from this study are first major steps towards this goal.
The pollen record is a powerful proxy to reconstruct past terrestrial vegetation, but quantifying plant abundances is strongly limited because plants produce pollen in different amounts and pollen is dispersed differently. Further complications arise from the use of percentage data. Finally, a pollen grain deposited at a site may have arrived from proximate or distant sources, which implies that a single pollen sample may reflect very different vegetation scenarios. Present thesis suggests improving quantitative reconstructions of past vegetation by refined calibration of the pollen-vegetation relationship (paper I) and application of the downscaling approach (papers II-IV). Paper I primarily addresses the questions of pollen production and dispersal by calibrating the pollen-vegetation relationship. Data analysis employs the common extended R-value (ERV) approach and a new data-model comparison method, which appears more suitable than the ERV approach. For the first time PPEs have been calculated using three contrasting pollen dispersal options, including a Lagrangian stochastic (LS) model. The study proves that the underlying pollen dispersal model is a crucial parameter in PPE calculations and that the calculations with the LS model produce more reliable and realistic PPEs. Papers II to IV address quantitative reconstructions of past vegetation. Using the newly developed downscaling approach, the three studies explore fine scaled vegetation patterns in NE Germany during the Late Glacial and early Holocene. The main assumption of the downscaling approach is that the present day pattern of abiotic site conditions (e.g. the pattern of soil substrates) existed, at least to a large extend, also during the study periods. The basic principle of the approach is to test, whether pollen deposition in sites across a landscape is correlated to that site pattern. The first application of the approach (paper II) has shown a close correlation between PINUS pollen percentages and the distance weighted abundance of sandy soils and between BETULA pollen percentages and the distance weighted abundance of morainic till during the Allerød period, indicating that pine and birch formed rather separate stands on either substrate type. The cooling of the Younger Dryas induced significant changes in the vegetation of NE Germany. By combining pollen percentage and pollen accumulation rate data paper III identified a sharp vegetation boundary between the Mecklenburg and Brandenburg area at about 53 °N. The downscaling approach, here used with pollen accumulation rate data, suggests that in the North small tree stands could only exist in sheltered positions. The sharp vegetation boundary is possibly related to a climatic gradient and the southern permafrost limit, which itself may result from the formation of sea ice on the North Atlantic north of 53°N during winter. The warming of the Holocene again allowed the expansion of forests in the study area. Paper IV uses high resolution pollen (accumulation rate) data to study the successive forest formation, including the immigration of hazel, and explores vegetation patterns and composition during these successive stages using the extended downscaling approach. This approach addresses the problems related to differential pollen production, dispersal and the use of percentage data by applying simulations. It reveals that initially pine and birch established, as during the Allerød period, in largely separate stands with pine dominating on sandy soils and birch dominating on fine grained soils. Also open rich vegetation persisted, possibly due to seasonal drought, mainly on fine grained soils. Hazel later mainly spread on sites that received additional wetness from ground or surface water; it did not enter pine dominated forests on well drained sandy soils. Overall, the early Holocene vegetation of the study area was sharply differentiated by soil humidity and fertility. To conclude, present thesis has revealed vegetation patterns and species site preferences in NE Germany during three periods of the Lateglacial and early Holocene. The results improve our understanding of vegetation history in northern Central Europe, specifically for periods of rapid climate change. The approaches applied are flexible with respect to the type and quality of pollen data used and may be implemented using standard software packages.
Significant alterations of cambial activity might be expected due to climate warming, leading to growing season extension and higher growth rates especially in cold-limited forests. However, assessment of climate-change-driven trends in intra-annual wood formation suffers from the lack of direct observations with a timespan exceeding a few years. We used the Vaganov-Shashkin process-based model to: (i) simulate daily resolved numbers of cambial and differentiating cells; and (ii) develop chronologies of the onset and termination of specific phases of cambial phenology during 1961–2017. We also determined the dominant climatic factor limiting cambial activity for each day. To asses intra-annual model validity, we used 8 years of direct xylogenesis monitoring from the treeline region of the Krkonoše Mts. (Czechia). The model exhibits high validity in case of spring phenological phases and a seasonal dynamics of tracheid production, but its precision declines for estimates of autumn phenological phases and growing season duration. The simulations reveal an increasing trend in the number of tracheids produced by cambium each year by 0.42 cells/year. Spring phenological phases (onset of cambial cell growth and tracheid enlargement) show significant shifts toward earlier occurrence in the year (for 0.28–0.34 days/year). In addition, there is a significant increase in simulated growth rates during entire growing season associated with the intra-annual redistribution of the dominant climatic controls over cambial activity. Results suggest that higher growth rates at treeline are driven by (i) temperature-stimulated intensification of spring cambial kinetics, and (ii) decoupling of summer growth rates from the limiting effect of low summer temperature due to higher frequency of climatically optimal days. Our results highlight that the cambial kinetics stimulation by increasing spring and summer temperatures and shifting spring phenology determine the recent growth trends of treeline ecosystems. Redistribution of individual climatic factors controlling cambial activity during the growing season questions the temporal stability of climatic signal of cold forest chronologies under ongoing climate change.
We studied a pristine, prominently patterned raised bog in Tierra del Fuego, Argentina, to disentangle the complex interactions among plants and water and peat. The studied bog lacks complicating features often posed by other bogs. It is completely dominated by Sphagnum magellanicum, which covers all niches and growth forms, and is joined by only a dozen higher plant species; it is entirely ombrotrophic with very sharp borders to the surrounding fen; it has only one type of peat that shows an only limited range in degree of decomposition; and it is situated in a very even climate with minimal differences in rainfall and temperature over the year. We present detailed measurements along a 498-m-long transect crossing the bog, including water table measurements (n = 498), contiguous vegetation relevés (n = 248), hydraulic conductivity just below the water table (n = 246), and hydraulic conductivity in 11 depth profiles (n = 291); degree of humification of the corresponding peat was assessed in conjunction with the hydraulic conductivity measurements (n = 537). Sphagnum magellanicum moss samples were collected every 2 m along this transect as well and genotyped (n = 242). In addition, along short, 26-m-long transects crossing strings and flarks water table and hydraulic conductivity just below the water table were measured every meter. Sphagnum growth forms were assessed, and the vegetation of the entire bog was mapped in 10 × 10-m relevés (n = 3322). A simulation model was applied to a generalized shape of the bog and produced surface patterns that well matched those seen in the field. The results were integrated with information from the literature and discussed in the framework of a self-regulating and self-organizing raised bog. We identified 19 hydrological feedback mechanisms. We found that the various mechanisms overlap in both space and time, which means there is redundancy in the self-regulation of the system. Raised bogs, when in a natural state, are among the most resilient ecosystems known; resilience that is provided by feedbacks and backup systems to these feedbacks.
Abstract
Climate change is increasing the frequency and intensity of drought events in many boreal forests. Trees are sessile organisms with a long generation time, which makes them vulnerable to fast climate change and hinders fast adaptations. Therefore, it is important to know how forests cope with drought stress and to explore the genetic basis of these reactions. We investigated three natural populations of white spruce (Picea glauca) in Alaska, located at one drought‐limited and two cold‐limited treelines with a paired plot design of one forest and one treeline plot. We obtained individual increment cores from 458 trees and climate data to assess dendrophenotypes, in particular the growth reaction to drought stress. To explore the genetic basis of these dendrophenotypes, we genotyped the individual trees at 3000 single nucleotide polymorphisms in candidate genes and performed genotype–phenotype association analysis using linear mixed models and Bayesian sparse linear mixed models. Growth reaction to drought stress differed in contrasting treeline populations. Therefore, the populations are likely to be unevenly affected by climate change. We identified 40 genes associated with dendrophenotypic traits that differed among the treeline populations. Most genes were identified in the drought‐limited site, indicating comparatively strong selection pressure of drought‐tolerant phenotypes. Contrasting patterns of drought‐associated genes among sampled sites and in comparison to Canadian populations in a previous study suggest that drought adaptation acts on a local scale. Our results highlight genes that are associated with wood traits which in turn are critical for the establishment and persistence of future forests under climate change.
Because Moringa is rich in secondary metabolites and phenolics, we faced a challenge in extracting a pure DNA required for AFLP (the first proposed genotyping method). Later, different DNA isolation methods were tested to overcome the obstacles caused by phenolics and sugars, an AFLP protocol that worked well with the cultivated seedlings at the botanical garden in Greifswald. The markers for the Internal Transcribed Spacer (ITS) were as well tested that showed a monomorphic structure between all samples. Finally, SSR (microsatellite) markers were established. To optimize DNA extraction, the method of Doyle and Doyle was modified and optimized. This is an ideal method for obtaining a non-fragmented DNA that could be used for AFLP. In addition, two other DNA extraction methods; (KingFisher Flex robot using Omega M1130 extraction Kits, and spin columns and 96-plates using Stratec kits). Although we achieved similar results for both Robot kits (Omega) and Stratec kits, the amplification for most of the samples extracted with Robot did not work, therefore the Stratec kit was the method of choice as it has also a lower cost, combined with a high quality of DNA. For ITS, no polymorphism was found for 28 samples of M. peregrina from Sinai (sequences submitted to GenBank). However, since microsatellite markers of M. peregrina were not known, it was a challenge to try a cross amplification from other species with well-known microsatellite primers. Cross-amplification of 16 primers known from the related species M. oleifera was tested, and three multiplex PCR reactions were established after testing different annealing temperatures and different primers concentrations. This included 13 primers out of the 16 investigated markers which gave a reliable band. All methods used for genetic assessments for the different Moringa species are compiled in a comparative review to look for connections between the different Moringa species. For Moringaceae, M. oleifera and M. peregrina are closely related to each other. Both species have slender trunks, with thick, tough bark and tough roots and bilaterally symmetrical flowers with a short hypanthium. All but one SSR markers used in this study are highly informative However, the degree of polymorphy varied considerably within the 13 markers used. The Probability of Identity (PI) for all loci was 2.6 x 10-9 with high resolution. The percentage of polymorphic loci for all populations was 88.5±2.2; figures for single populations were 92.3%, 84.6%, 84.6%, and 92.3% for the wadis WM, WA, WF, and WZ, respectively. The genotype accumulation curve as well demonstrated that 7–8 markers were necessary to discriminate between 100% of the multilocus genotypes. Significant departures from HWE were detected for eight loci (P < 0.001), probably due a high degree of inbreeding within population. The observed (HO) and expected (HE) heterozygosities ranged from 0 to 0.86 and from 0 to 0.81, respectively. However, for the pooled population, excluding the monomorphic locus MO41, HO and HE ranged from 0.069 to 0.742 and from 0.126 to 0.73 with averages of 0.423 and 0.469, respectively. The mean of FST was 0.133, indicating that, due to the long generation time of M. peregrina, there is still relatively little differentiation between the four remaining populations. An analysis of molecular variance (AMOVA) revealed that the old populations of M. peregrina are still genetically diverse where 75% of variance was recorded within individuals and 83% within populations. An analysis with STRUCTURE, varying the parameter K between 1 and 7, revealed the most pronounced genetic structure for K=3, thus uniting the populations from two neighboured wadis (W. Agala and W. Feiran). The three groups seem to be now genetically isolated. (They may be remainders of a formerly contiguous population, especially when considering the change towards a drier climate in Northern Africa within the last 6000 years). Six clones of each two individuals collected from the same wadi were found, pointing to vegetative dispersal via broken twigs, which may have rooted after flash floods. It may be an alternative mode of reproduction under harsh conditions. Our data reveal a low gene flow between three of the four wadis, suggesting that the trees are relictual populations. In general, conservation of populations from the three genetically most diverse wadis and cross-breeding of trees within a reforestation program is recommended as an effective strategy to ensure the survival of M. peregrina at Sinai, Egypt.
Myxomycetes (Amoebozoa, plasmodial slime molds) are one of the last larger groups of organisms where the biodiversity is not yet investigated by molecular methods, except for a very few cultivable model species. Based on the first phylogenies for the group produced in 2012 and 2013, this thesis work explores the genetic diversity of wild populations of myxomycetes, addressing two questions: 1. Does diversity and phylogenetic trees found with barcode markers fit the current morphological species concept, and do barcode markers reveal a lower or higher diversity than found by morphological characters? In the first case, morphological characters seen as decisive for species differentiation would be plastic (shaped by the environment), in the second case we must assume the existence of cryptic species. 2. Can genetic markers be used to see if natural populations of myxomycetes reproduce mainly sexual or asexual? Sexuality is proven to occur in the Amoebozoa, but asexual reproduction should be advantageous for habitat colonization. Experiments with cultivable species have shown that both reproductive modes occur in the myxomycetes. Two species complexes were chosen for an in-depth investigation. The first species is the common wood-inhabiting myxomycete Trichia varia (Pers. ex J.F. Gmel.) Pers., one of the first myxomycetes to be described and always seen as a variable, yet single, species. The second example involves a snowbank species so far known as Lamproderma atrosporum Meyl., which was recently transferred to a genus on its own, Meriderma Mar. Mey. & Poulain, and a morphological species concept, including several taxa, was proposed. Trichia varia belongs to the bright-spored myxomycetes. Partial sequences of three independent markers (nuclear small-subunit ribosomal RNA gene, SSU, extrachromosomal; protein elongation factor 1 alpha gene, EF1A, chromosomal; cytochrome oxidase subunit 1 gene, COI, mitochondrial) from 198 specimens resulted in a three-gene phylogeny containing three groups, within each group combinations of the single-marker genotypes occurred exclusively. Complete SSU sequences were generated for 66 specimens, which revealed six positions that can carry group I introns and putatively functional or degenerated homing endonuclease genes in two groups. All observations (genotypic combinations of the three markers, signs of recombination, intron patterns) fit well into a pattern of three cryptic biological species that reproduce predominantly sexual but are reproductively isolated. The pattern of group I introns and inserted homing endonuclease genes mounts evidence that the Goddard-Burt intron life cycle model applies to naturally occurring myxomycete populations. A total of 89 specimens of the dark-spored myxomycete genus Meriderma from five European mountain ranges were sequenced for partial genes of SSU and EF1A. The latter gene includes an extremely variable spliceosomal intron. Three clades, the two morphologically recognizable taxa M. fuscatum, M. aggregatum, and the morphologically complicated complex species M. atrosporum agg., were recovered. The EF1A-based phylogeny of the 81 specimens of M. atrosporum agg. resulted in seven subclades, with the two EF1A-haplotypes of a sequence sharing always one subclade for each of the 50 heterozygous specimens, a pattern consistent with the existence of several independent but sexually reproducing biospecies. Identical EF1A genotypes occurred more often within a regional population than in between. A simulation assuming panmixis within a biospecies but not in between, and isolation between mountain ranges suggested that similar numbers of shared genotypes can be created by chance through sexual reproduction alone. Numbers of haplotypes shared between mountain ranges correlate with geographical distance, suggesting occasional long-distance dispersal by spores. An enlarged data set containing 227 partial SSU sequences of Meriderma spp. identified 53 ribotypes, with a ribotype accumulation curve indicating 68.4±14.5 ribotypes to expect according to the Chao2 estimator. The topology of the SSU phylogeny generally confirms results from the partial SSU and EF1A data set of 89 specimens, where several putative biospecies could be recognized. A novel method for automated analyses of SEM images allows to derive quantitative descriptors for spore ornamentation, which were subjected to multivariate analyses. Spore ornamentation provided traits with the highest explanatory power in a multivariate statistics, whereas spore size and stalk length were much less significant. For some but not all putative biospecies a unique combination of morphological characters was found, which is in accordance with the hypothesis of instant sympatric 8 speciation via mutations creating incompatible strains splitting from existing biospecies. The morphologically recognizable taxa of the genus are described and a key for the genus Meriderma is given. To compare morphological and molecular diversity in lignicolous myxomycetes, all specimens found in a study covering the late-autumn aspect were sequenced, using partial SSU gene as a barcode marker. A total of 161 logs in the old-growth forest Eldena, northeastern Germany, was surveyed, resulting in 530 collections representing 27 taxa from 14 genera. Bright-spores species were far more abundant than dark-spored taxa. A phylogeny based on partial SSU sequences for bright-spored myxomycetes revealed morphospecies to be largely consistent with phylogenetic groups. Most but not all morphospecies may contain multiple ribotypes that cannot be differentiated by light microscopy. This first study backing up a traditional morphology-based survey by a full molecular component demonstrates that partial SSU sequences can function as reliable barcode markers for myxomycetes, but reveals as well a significant, yet not infinite, amount of hidden diversity. The main conclusions of this work, set up in the frame of a project funded by the German Research Council (DFG), are the following: 1. Sexual reproduction seems to be an important, if not the dominating mode (apart from clonal myxamoebal populations built up by binary fission) of reproduction in naturally occurring populations of myxomycetes. 2. From the two investigated species complexes we can expect many, if not most, morphopecies to be composed of reproductively isolated, sexually reproducing, biospecies. 3. Partial SSU sequences, as most widely used in this study, seem to represent suitable barcode markers for the group and can be used to distinguish the (usually cryptic) biospecies, although they alone do not allow any conclusions about reproductive isolation and speciation processes. 4. We have to expect a significant amount of hidden diversity in myxomycetes, which will increase the number of taxa from ca. 1000 recognized morphologically by a factor between two and ten.
Abstract
Myxomycetes are terrestrial protists with many presumably cosmopolitan species dispersing via airborne spores. A truly cosmopolitan species would suffer from outbreeding depression hampering local adaptation, while locally adapted species with limited distribution would be at a higher risk of extinction in changing environments. Here, we investigate intraspecific genetic diversity and phylogeography of Physarum albescens over the entire Northern Hemisphere. We sequenced 324 field collections of fruit bodies for 1–3 genetic markers (SSU, EF1A, COI) and analysed 98 specimens with genotyping by sequencing. The structure of the three‐gene phylogeny, SNP‐based phylogeny, phylogenetic networks, and the observed recombination pattern of three independently inherited gene markers can be best explained by the presence of at least 18 reproductively isolated groups, which can be seen as cryptic species. In all intensively sampled regions and in many localities, members of several phylogroups coexisted. Some phylogroups were found to be abundant in only one region and completely absent in other well‐studied regions, and thus may represent regional endemics. Our results demonstrate that the widely distributed myxomycete species Ph. albescens represents a complex of at least 18 cryptic species, and some of these seem to have a limited geographical distribution. In addition, the presence of groups of presumably clonal specimens suggests that sexual and asexual reproduction coexist in natural populations of myxomycetes.
Over thousands of years, peatlands around the world have accumulated carbon (C) stocks of global importance. Drainage for agriculture, forestry and peat extraction has transformed many peatlands from long-term sinks into strong sources of carbon dioxide (CO2). Peat extraction is worldwide responsible for about ten percent of drained peatlands and is mainly carried out in northern countries and Eastern Europe. In Belarus, 0.3 Mha of peatlands are drained for peat extraction, which is twelve percent of the country's peatland area. From 2006 to 2013, 21,333 ha of this area have been rewetted to protect these peatlands from fire and further degradation, reduce their greenhouse gas (GHG) emissions, turn them back into C sinks and promote biodiversity. A further 260,000 ha are no longer used for peat extraction and their rewetting would be a great benefit for nature conservation and climate protection.
Rewetting of abandoned peat extraction areas usually leads to inundation of large areas where not adapted plants die and new species establish, depending on water level and nutrient conditions. Beavers, of which there are many in Belarus, also play an important role in the rewetting of peatlands. They dam up ditches in drained and rewetted peatlands, thus contributing to water level increases and vegetation changes. The aim of this PhD thesis was to investigate the impact of inundation on vegetation and GHG emissions in formerly extracted fens in Belarus, to determine the role of water level in this process, and to study whether such fens develop back into C sinks with an almost neutral GHG balance within one or two decades after rewetting (Papers II and III). Also the potential of beaver activities for peatland restoration was assessed (Paper III).
Two very different fens, rewetted after peat extraction, were chosen as study areas. The first one, Giel'cykaŭ Kašyl, is a former flood mire and was rewetted with water from the Jasiel'da River in 1985. During the study period 2010–2012 this site was a shallow lake (~ 1 m deep) dominated by very productive, tall reed. Shallower areas along the edges had a partly floating vegetation cover of cattail (Typha latifolia, T. angustifolia) and sedges (Carex elata, C. vesicaria). The second fen, Barcianicha, is fed by groundwater. Rewetting from 1995 onwards resulted in water levels at or slightly above surface and a lower nutrient availability compared to Giel'cykaŭ Kašyl'. This was reflected in the establishment of mesotrophic communities of Eriophorum angustifolium and Carex rostrata. Phragmites australis stands, which were also dominant here, were shorter and less productive than in Giel'cykaŭ Kašyl'. The southern area of Barcianicha was not used for peat extraction and has not been rewetted. Until 2009 vegetation of this part was characterized by forbs (Urtica dioica) and wet meadows (Agrostis stolonifera). From autumn 2009, a beaver dam in the main drainage ditch caused flooding of these areas and led to diverging vegetation development depending on water levels.
Within the framework of this doctoral thesis annual fluxes of CO2, methane (CH4) and nitrous oxide (N2O) and the development of water levels and vegetation were monitored for two years at nine sites and evaluated (Papers II and III). Three of the sites, respectively, were located (a) in Giel’cykaŭ Kašyl’, flooded in 1985, (b) in the central area of Barcianicha, which was rewetted in 1995, and (c) in the southern part of Barcianicha, which was flooded by beavers end of 2009. GHG measurements were carried out with manual chambers from August 2010 to September 2012. Annual net CO2 exchange rates (NEE) were modeled based on light response curves of gross primary production (GPP) and on temperature response curves of ecosystem respiration (Reco), which were determined every third to fourth week by alternating measurements with transparent (cooled) and opaque chambers (both with fan) along the daily amplitude of photosynthetically active radiation (PAR) and temperature. Annual CH4 emissions were calculated mainly based on the temperature response of CH4 fluxes over the course of the year, based on biweekly (in summer) to monthly (in winter) repeated single measurements with opaque chambers (without fan). This was done, although all longer rewetted sites were dominated by aerenchymatic plants whose gas transport during the vegetation period may change over the course of the day and can be influenced by shading. This might apply to the six longer rewetted sites, two of which were dominated by Phragmites australis, and the others by Typha latifolia, Carex elata, Carex rostrata or Eriophorum angustifolium. For these six sites therefore studies on the daily course of CH4 release and the influence of chamber shade were conducted, covering 8–24 hours and lasting at least from sunrise to afternoon. Also the extent to which flux rates were affected by a lack of chamber headspace mixing by fans was investigated in the mentioned studies (Papers I and II).
The daytime course of CH4 emissions showed a pronounced dynamic for Phragmites australis in both fens, with minimum release during the night and maximum during the day (Paper I). The other sites in contrast did not show a significant diurnal CH4 flux dynamic (Paper II). Lack of headspace mixing by fans as compared to chambers with fan resulted in a slight underestimation of CH4 emissions at very high chambers (220 and 250 cm), as used for Phragmites australis in Giel'cykaŭ Kašyl', while there was no difference at lower chambers (≤185 cm), as used for the other sites. Opaque chambers resulted for sites dominated by Typha latifolia and Carex elata in significantly (1.2 times and 1.1 times, respectively) lower CH4 fluxes compared to transparent chambers. For the other sites, opaque chambers did not significantly reduce CH4 emissions. This result was unexpected, especially for Phragmites australis, as PAR out of all parameters tested had the strongest influence on CH4 emissions from both reed sites, and clouds directly led to reduction of their emissions. Presumably the gas flow in the reed shoots located within opaque chambers was maintained by shoots outside the chamber that were connected to the enclosed shoots by rhizomes (Paper I). The investigations showed that single measurements between 9 a.m. and 6 p.m. with opaque chambers without fan, as performed for the determination of annual CH4 fluxes, resulted for Carex rostrata and Eriophorum angustifolium in estimates similar to the daily mean, but for Phragmites australis in estimates that were rather above the daily mean. Annual CH4 fluxes from Phragmites australis could therefore be slightly overestimated. CH4 fluxes from Typha latifolia and Carex elata during the vegetation period were corrected by a factor of 1.2, although darkness inside of opaque chambers matters only at day, not at night. Daily and annual CH4 fluxes from these sites have been therefore most likely slightly overestimated, too.
Water saturation and the establishment of adapted vegetation were the most important conditions for the restoration of C sinks (gaseous CO2 and CH4 fluxes) in the investigated peatlands. The only site with falling water levels in summer and thus temporarily aerated peat was the beaver flooded forbs (Urtica dioica) site at Barcianicha. This site was a very strong CO2 emitter and the only significant N2O source of the entire study (Paper III). All other sites were permanently wet, had much lower CO2 emissions or were even net C sinks (Papers II and III). Establishment of adapted vegetation depended on inundation depth and time since rewetting. For example, within one year the meadow site in Barcianicha shallowly flooded by beaver was colonized by Carex rostrata and other adapted helophytes and developed into a CO2 sink, while the deeper flooded site at the same meadow initially attracted only Chara and some individuals of Alisma plantago aquatica and remained a moderate CO2 source. However, the results of the longer rewetted sites show, that also deeply (~ 1 m) flooded fen areas can become densely populated with mire plants in the course of 25 years and develop into net C sinks. Highest annual C uptake in both fens was achieved by the reed sites. Eriophorum angustifolium and Carex rostrata in mesotrophic Barcianicha were smaller C sinks. Typha latifolia and Carex elata in the eutrophic Giel'cykaŭ Kašyl', on the other hand, released CO2, presumably because the high and fluctuating water levels imposed stress to the plants, and because the large supply of nutrients and dead plant material allowed for strong heterotrophic respiration (Paper II). The simultaneously high CH4 emissions made Typha latifolia and Carex elata major sources of GHG. CH4 emissions from Phragmites australis in Giel'cykaŭ Kašyl' were even higher, but due to extremely high CO2 uptake the site was only a small net GHG source. CH4 emissions in Barcianicha were much lower and comparable to undisturbed sedge fens. The difference between Giel'cykaŭ Kašyl' and Barcianicha was mainly due to the different nutrient supply and the related productivity of the plants. Important conclusions are that stable inundation is an appropriate measure for restoration of the C sink of formerly extracted fens, but nutrient input with water needs to be stopped or reduced in order to decrease CH4 production. If this is not possible, establishment of Phragmites australis and other strong C sinks could help to compensate for the climate impact of high CH4 emissions from eutrophic sites.
The effect of the beaver dam on the development of the southern part of Barcianicha depended not only on the initial situation but mainly on the water level. Under optimal conditions, it led to the rapid establishment of adapted mire plants, the restoration of a C sink and a significant reduction of GHG emissions. However, this situation in the shallowly flooded meadow was achieved by chance. In comparison to planned rewetting measures, which aim to raise the water level evenly over the entire peatland, beavers dam ditches in order to improve their immediate habitat, thus influencing water levels only up to a certain distance, but rarely over the entire peatland. Nevertheless, beaver activity is of high value both for mire conservation projects, where existing dams are supplemented by beaver dams, and for abandoned, drained peatlands, like former peat extraction areas in Belarus, many of which at least partially have been rewetted by beavers.
Human-driven peatland drainage has occurred in Europe for centuries, causing habitat degradation and leading to the emission of greenhouse gases. As such, in the last decades, there has been an increase in policies aiming at restoring these habitats through rewetting. Alder (Alnus glutinosa L.) is a widespread species in temperate forest peatlands with a seemingly high waterlogging tolerance. Yet, little is known about its specific response in growth and wood traits relevant for tree functioning when dealing with changing water table levels. In this study, we investigated the effects of rewetting and extreme flooding on alder growth and wood traits in a peatland forest in northern Germany. We took increment cores from several trees at a drained and a rewetted stand and analyzed changes in ring width, wood density, and xylem anatomical traits related to the hydraulic functioning, growth, and mechanical support for the period 1994–2018. This period included both the rewetting action and an extreme flooding event. We additionally used climate-growth and climate-density correlations to identify the stand-specific responses to climatic conditions. Our results showed that alder growth declined after an extreme flooding in the rewetted stand, whereas the opposite occurred in the drained stand. These changes were accompanied by changes in wood traits related to growth (i.e., number of vessels), but not in wood density and hydraulic-related traits. We found poor climate-growth and climate-density correlations, indicating that water table fluctuations have a stronger effect than climate on alder growth. Our results show detrimental effects on the growth of sudden water table changes leading to permanent waterlogging, but little implications for its wood density and hydraulic architecture. Rewetting actions should thus account for the loss of carbon allocation into wood and ensure suitable conditions for alder growth in temperate peatland forests.
Peatlands are wetland ecosystems covering a relatively small area of the World (~3%), but at the same time storing excessive amounts of carbon for a very long time (equivalent to the four times global annual net primary production). As carbon sinks, peatlands work in spite of their slow growth, absorbing carbon dioxide (CO2) through the photosynthetic activity of the peatland plants and their low growth rates, and because high groundwater table removes oxygen from the soil and slows down the decomposition of the dead plant matter. Because of the relative lack of the oxygen in the peat, especially compared to the mineral soils, methanogen populations in the peatlands are abundant, and releasing methane (CH4), a potent greenhouse gas, to the atmosphere. Therefore, peatlands are generally at the same time significant carbon sinks and stores as well as the methane sources. The balance among the two peatland gass fluxes (CO2 and CH4) will dictate the impact of any given peatland on the global climate and primarily driven by hydrology, in the form of the groundwater table levels.
Because of the slow decomposition rates, and from radiocarbon dating of the peat as well as the subfossil records buried in it, carbon stored in peatlands is locked for a very long time (centuries to millennia). It is, therefore, crucial to gain insights into the development of peatlands and their gas balance through time. One way to get both is by studying peatland hydrology in the form of the groundwater table levels and their historical variations. Unfortunately, intensive monitoring of peatland groundwater table, when available, is an only a recent endeavor. Therefore, we need to employ proxies to reconstruct the past by leveraging the present. In statistics, proxy variables are often used when the observations of the variable of interest, are either missing or too difficult to obtain.
In this thesis, I tested whether we can use the radial growth of the Scots pines growing on peat as proxies to the peatland hydrology. To that end, I studied growth responses of the peatland Scots pines. Other proxies can and are used for the reconstructions of the groundwater table levels, but tree-growth is widely used as one of the proxies to reconstruct past environments which is at the same time annually resolved.
First, I examined the growth ecology of the peatland Scots pines by looking at their intra-annual development and trying to find relationships between it and environmental factors while at the same time comparing it with the Scots pines growing at the forest sites. I first tried with wood anatomy and found that, unfortunately, peatland Scots pines do not form enough wood cells, and consequently do not have high temporal resolution, necessary to investigate the intra-annual patterns of the radial growth. Initial results from wood anatomical investigations were interesting none-the-less, indicating that peatland Scots pines might have smaller cell features than the Scots pines from forests, but might at the same time maintain Early/Latewood ratios of those same features.
After I found that wood anatomical series were not resolved enough I decided to go with dendrometers, linear displacement sensors which constantly monitor the variations of stem radius, to get insights into the intra-annual growth patterns of the peatland Scots pines. Before using dendrometers for ecological investigations, I was involved in implementing routines commonly used in the analysis of the dendrometer signals and bringing them to R in the form of the dendrometeR package.
At one peatland complex, I installed dendrometers on ten trees in total at both peatland and forest sites and compared the pattern of the standardized signal. I inferred from the comparisons and classifications that the signal from two sites was indistinguishable for the dendrometer series shorter than five days. Furthermore, the most important environmental factor driving the radial variation at the peatland site was hydrological, daily relative humidity, indicating further that peatland hydrology might indeed be the driver behind peatland Scots pine growth.
Finally, I looked at the growth responses of peatland Scots pines from central Estonia using dendrochronological methods. Peatland hydrology, in the form of the groundwater table levels, was indeed the environmental factor with the strongest, and also stationary, correlations with the radial growth of the peatland Scots pine. That relationship indicated that peatland Scots pines are indeed possible proxies for reconstructing past levels of the peatland groundwater tables.
My study further indicated that the growth response of the peatland Scots pines was non-linear, further complicating the reconstructions of the past peatland hydrology. However, the strength of the growth response was proportional to the general hydrological regime, expressed as median groundwater table level. As the hydrological regime of the peatland does not vary considerably on the annual scales, but more on decadal it might be more appropriate to find another, independent, proxy to the hydrological regime first, and than use annually resolved radial growth of the peatland Scots pine to reconstruct past levels of the peatland groundwater table.
Aim
Climate change challenges temperate forest trees by increasingly irregular precipitation and rising temperatures. Due to long generation cycles, trees cannot quickly adapt genetically. Hence, the persistence of tree populations in the face of ongoing climate change depends largely on phenotypic variation, that is the capability of a genotype to express variable phenotypes under different environmental conditions, known as plasticity. We aimed to quantify phenotypic variation of central Europe's naturally dominant forest tree across various intraspecific scales (individuals, mother trees (families), populations) to evaluate its potential to respond to changing climatic conditions.
Location
Europe.
Time Period
2016–2019.
Major Taxa Studied
European beech (Fagus sylvatica L.).
Methods
We conducted a fully reciprocal transplantation experiment with more than 9000 beech seeds from seven populations across a Europe-wide gradient. We compared morphological (Specific Leaf Area), phenological (leaf unfolding) and fitness-related (growth, survival) traits across various biological scales: within single mother trees, within populations and across different populations under the contrasting climates of the translocation sites.
Results
The experiment revealed significant phenotypic variation within the offspring of each mother tree, regardless of geographic origin. Initially, seedling height growth varied among mother trees and populations, likely due to maternal effects. However, the growth performance successively aligned after the first year. In summary, we observed a consistent growth response in different beech populations to diverse environments after initial maternal effects.
Main Conclusions
The study strikingly demonstrates the importance of considering intraspecific variation. Given the surprisingly broad spectrum of phenotypes each mother tree holds within its juvenile offspring, we conclude that Fagus sylvatica might have the potential for medium-term population persistence in face of climate change, provided that this pattern persists into later life stages. Hence, we also suggest further investigating the inclusion of passive adaptation and natural dynamics in the adaptive management of forests.