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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.