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Planning Modes for Major Transportation Infrastructure Projects (MTIPs): Comparing China and Germany
(2018)
Recent climate change has affected the forest system comprehensively. Northern hemisphere elevational treelines are considered as a key environment for monitoring the effects of current anthropogenic climate change. Moreover, trees from these areas are also widely employed in paleo-climate reconstructions. The stability of the tree growth climate relationship under current scenario is crucial for all tree ring based climate researches. It is important to investigate how trees respond to this rapid environmental change at altitudinal treelines. Tree cores from 21 treeline sites of three species (Pinus tabulaeformis, Picea crassifolia, and Sabina przewalskii) from Northeastern Tibetan have been conducted in this thesis. The instable correlations between tree growth and climate are the general response pattern of trees from all study sites in NE Tibetan Plateau. Picea crassifolia shows the most instable response to climate factors (mean monthly temperature and total monthly precipitation). Pinus tabulaeformis and Sabina przewalskii just showed instable and divergent responses to their main limiting climate factors but no clear trend was found which is limited by the few sample sites. Corresponding to divergent responses of Picea crassifolia to mean monthly temperature, most radial growth of Picea crassifolia were inhibited by this climate change type drought, only few trees within same sites grew faster due to temperature increasing during recent decades. The divergence response mainly started in last 30 years in six of eleven sample sites over the Northeastern Tibetan Plateau. North-westerly drier sites showed a large percentage of trees per site with a negative correlation to temperature and mostly southerly moister sites showed more mixed responses with both negatively and positively responding trees within site. Concurrent with the regional pattern, low elevation sites show mostly negative correlations with temperature and high elevation sites show more mixed responses. As the hydrothermal conditions of the investigation area changed to a drier and warmer combination, drought stress on tree growth have been intensifying over time and expanding spatially from the middle to most of our study area during the last half century. The Picea crassifolia tree growth climate relationship conducted on an elevational gradient with four different levels from upper treeline to lower treeline at the NE Tibetan Plateau. Results show that upper treeline trees show divergent growth trends and divergent responses in recent decades. Trees from lower treeline show a strengthening drought stress signal over time and no divergent growth trends within sites. This potential ecological reaction of tree populations to changing environmental conditions shows an implications for using trees to reconstruct climate, since the indiscriminate use of tree ring data from sites showing opposite responses to increasing warming could cause mis-calibration of tree ring based climate reconstructions, and over- or underestimation of carbon sequestration potential in biogeochemical models. The physiological response of Sabina przewalskii tree growth to major limiting climate factors based on the Vaganov-Shashkin (VS) model indicated that precipitation during the early growing season, especially in May and June, has significant effect on tree growth, while temperature mainly affects tree growth by warming-induced drought and by extending the growing season in the NE Tibetan Plateau. Under current and projected climate scenarios, modeling results predict an increase in radial growth of Sabina przewalskii around the Qaidam Basin, with the potential outcome that regional forests will increase their capacity to sequester carbon. However, most Picea crassifolia trees growing at lower elevations than Sabina przewalskii might be continue stressed by the warming induced drought and might decrease radial growth in future.
For many years, rangeland ecologists have debated about whether the state of semi-arid and arid rangelands is the expression of an ecological equilibrium or non-equilibrium dynamics reached in response to grazing livestock. Since the problem has been considered at different spatial scales, it is recognised that the competing concepts of equilibrium and non-equilibrium dynamics need to be integrated. Furthermore, the role of environmental variables as vegetation driving factors has long been ignored in the discussion on grazing effects on ecosystems. Present thesis, examines the dependence of plant communities on environmental in particular site-ecological conditions in three ecosystems of Western Mongolia established along a precipitation gradient to detect the vegetation-driving ecological factors involved. Furthermore, grazing impact is exemplary assessed in a desert steppe at additional spatial scales of plant communities and population. At the landscape level, a classification of plant communities in dependence on environmental conditions is carried out. Additionally, the investigations focused on the impact of grazing on soil and on the occurrence of grazing-mediated plant communities. Data were sampled along an altitudinal gradient between 1150 m to 3050 m a.s.l. from arid lowland with desert steppe via semi-arid mountain steppe to humid alpine belt. Within each altitudinal belt, data sampling was carried out along grazing gradients, established from grazing hot spots to areas distant from them. By means of an environmentally based vegetation classification, factors with highest explanation values for largest variation in vegetation were identified and considered as most responsible for vegetation patterns. To validate and affirm the classification, three different statistical methods are applied: environmentally adjusted table work of vegetation relevés supported by cluster analysis of species distribution, detrended correspondence analysis of vegetation data separately from environmental data, and the principle component analysis of only environmental data. Vegetation-driving factors change along the altitudinal gradient from abiotic forces in the desert steppe, as e.g. altitude and soil texture, to abiotic and biotic forces in the alpine belt represented by soil texture, soil nutrients and grazing. Vegetation and soil of all ecosystems respond to grazing but with different patterns and to a different extent. While desert steppe does not indicate grazing communities, mountain steppe demonstrates grazing communities at fertilised sites and alpine belt at nutrients depleted sites. Thus, the grazing sensitiveness of the ecosystems is assumed to be linked with plant productivity and the role of vegetation as site-determining factor (Chapter 2). To examine grazing impact at lower spatial scales on desert steppe as the ecosystem with lowest grazing sensitiveness at the landscape scale, at community scale the total number of species, the total vegetation cover, the percentage of annual species, the cover of annual species, and properties of soil nutrient along gradients of grazing intensity within three different communities were assessed. Vegetation parameters respond to grazing in different ways, and the responses of the same parameters vary between plant communities. Correlations with grazing intensity indicate only partly statistical significance. Significant correlations of grazing intensity with concentrations of soil nutrient point to eutrophication in two communities. A comparison of vegetation and soil properties refers to a greater indirect influence of grazing via increased soil nutrients than the direct effect on vegetation (Chapter 4). At the population level, data about stand density, aboveground biomass, individual plant weight, and the proportion of flowering plants of the dominant dwarf semi-shrub Artemisia xerophytica were collected along a grazing gradient. Soil data were used to distinguish between grazing and edaphic influences. All parameters of Artemisia xerophytica reflect the assumed gradient of grazing intensity up to 800 m distance from the grazing hot spot. As grazing pressure decreases, plant density and total biomass per plot increase. The average shrub weight, an indicator of plant vitality, is related to both: distance from the grazing hot spot and stand density, which may be explained by additional intraspecific competition at higher densities. At a longer distance, these effects are masked by variations in soil parameters determining water availability, leading to quite similar degradation forms. These results are in contrast to other studies carried out at the scale of plant communities which did not detect significant changes along a grazing gradient. One explanation is the different map scale: the study took place only within a single plant community comparing populations of one species (Chapter 3). The comparative study demonstrates that even arid desert steppes of western Mongolia display equilibrial and non-equilibrial properties, depending on the observational scale: while no grazing mediated plant communities could be identified at the landscape scale as predicted by the non-equlilibrium model, at the community level vegetation parameters imply an intermediate position between equilibrium and non-equilibrium system. At the population level, the results clearly reflect the grazing gradient as predicted by the equilibrium model (Chapter 4). As a consequence, the assessment of vegetation dynamics and grazing impact in rangelands requires a multiple-scale approach that duly considers different vegetation properties responding differently to grazing, climatic and edaphic variability at different spatial scales. It is further suggested, that future research should draw comparisons between landscapes that co-evolved with herbivory, and those that did without (Chapter 4).
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.
Forests influence the climate of our Earth and provide habitat and food for many species and resources for human use. These valuable ecosystems are threatened by fast environmental changes caused by human-induced climte change. Negative growth responses and higher tree mortality rates were associated with increasing physiological stress induced by global warming. Especially boreal forests at high latitudes in the arctic region are threatened, a region predicted to undergo the highest increase in temperature during the next decades. Therefore, it is important to assess the adaptation potential in trees. For this purpose, I studied natural populations of white spruce (Picea glauca (Moench) Voss) in Alaska. In this thesis, I present three scientific papers in which my co-authors and I studied the phenotypic plasticity and genetic basis of tree growth, wood anatomy and drought tolerance as well as the genetic structure of white spruce populations in contrasting environments. We established three sites representing two cold-limited treelines and one drought-limited treeline with a paired plot design including one plot located at the treeline and one plot located in a closed-canopy forest, respectively. Additionally, the study design included one forest plot as reference. Within the entire project, in total 3,000 trees were measured, genotyped and dendrochronological data was obtained. I used several approaches to estimate the neutral and adaptive genetic diversity and phenotypic plasticity of white spruce as a model organism to explore the adaptation potential of trees to climate change.
In the first chapter, I combined neutral genetic markers with dendrochronological and climatic data to investigate population structure and individual growth of white spruce. Several individual-based dendrochronological approaches were applied to test the influence of genetic similarity and microenvironment on growth performance. The white spruce populations of the different sites showed high gene flow and high genetic diversity within and low genetic differentiation among populations, rather explained by geographic distance. The individual growth performances showed a high plasticity rather influenced by microenvironment than genetic similarity.
In the second chapter, I investigated the populations of the drought and cold-limited treeline sites to decipher the underlying genetic structure of drought tolerance using different genotype-phenotype association analyses. Based on tree-ring series and climatic data, growth declines caused by drought stress were identified and the individual reaction to the drought stress event was determined. A subset of 458 trees was genotyped, using SNPs in candidate genes and associated with the individual drought response. Most of the associations were revealed by an approach which took into account small-effect size SNPs and their interactions. Populations of the contrasting treelines responded differently to drought stress events. Populations further showed divergent genetic structures associated with drought responsive traits, most of them in the drought-limited site, indicating divergent selection pressure.
In the third chapter, my co-authors and I studied xylem anatomical traits at one of the cold-limited treeline sites to investigate whether genetic or spatial grouping affected the anatomy and growth of white spruce. Annual growth and xylem anatomy were compared between spatial groups and between genetic groups and individuals. Overall, wood traits were rather influenced by spatial than genetic grouping. Genetic effects were only found in earlywood hydraulic diameter and latewood density. Environmental conditions indirectly influenced traits related to water transport.
In conclusion, white spruce showed a high genetic diversity within and a low genetic differentiation among populations influenced by high gene flow rates. Genetic differences among populations are rather caused by geographical distance and therefore genetic drift. Differing selection pressure at the treeline ecotones presumably lead to divergent genetic structures underlying drought-tolerant phenotypes among the populations. Thus, adaptation to drought most likely acts on a local scale and involves small frequency shifts in several interacting genes. The identified genes with adaptive growth traits can be used to further exlore local adaptation in white spruce. Tree growth and wood anatomical traits are rather influenced by the environment than genetics and showed a high phentoypic plasticity. The high genetic diverstiy and phenotypic plasticity of white spruce may help the species to cope with rapid environmental changes. Still, additional work is needed to further explore adaptation processes to estimate how tree species reacted to rapid climate change. The presented thesis shed some light on the adaptation potential of trees by the example of white spruce using several approaches.
Global climate change is occurring all over the world, but in the Arctic the climate is changing more rapidly and drastically than in many other parts of our planet. Many species that are already at their climatic limit need to adapt to recent climate conditions or migrate in order to not go extinct. The possibilities of adaption include phenotypic plasticity and adaptation to various extents. This is also the case for white spruce P. glauca, which belongs to the conifers and thus in the largest group of gymnosperms still living today. Among the approx. 600 extant conifer species white spruce is one of the most widespread trees in North American boreal forests. Its range extends from 69° N in the Canadian Northwest Territories to the Great Lakes at about 44° N, where it occurs from sea level to an altitude of about 1520 m (Burns and Honkala, 1990). Site related, climate-dependent differences in white spruce reproduction can be seen as a strategy to survive under the harsh climatic conditions at Alaska's treelines: Besides sexual reproduction, the vegetative propagation occurs in the white spruce as an additional reproductive mechanism. This can be realized by "layering" when the lower branches of the tree crown touch the ground and develop roots to later grow as a separate individual with or without a connection to the mother tree. Known as other mechanisms of vegetative propagation are also the rooting of fallen trees which were not completely uprooted, and the "root suckering", in which new shoots sprout from the roots of the tree. However, the latter was not yet observed in the genus Picea. With the help of short, repetitive, non-coding sequences in the genome, which are therefore not subject to selection and are called microsatellites, these clones can be determined by genotyping.
For this purpose, using different polymorphic microsatellites, an individual multilocus genotype is created for each tree, by means of which it can be compared with all other trees of the same species.
In the first part of this work (article I), the occurrence of clones in three study areas at Alaskan treelines are examined and the reasons for their appearance in variable numbers are discussed. For this purpose, 2571 white spruces (P. glauca) were genotyped and their position was determined via differential GPS in the field. The percentage of clonal trees is higher in areas with harsh climatic conditions and correlates with the height of the lowest branches of the tree crown. This suggests that the vegetative propagation of white spruce is a backup strategy for times when climatic conditions hamper sexual reproduction. The correlation between clone numbers and tree crown height suggests "layering" as the main mechanism for cloning whereas selection for vegetative reproduction seems to be very unlikely shown by the results for genetic differentiation between the clonal and the singleton trees in this study.
In the second part of this work (articles II and III), the influence of environmental factors and phenotypic traits on the mycobiome of the needles (including all fungi living on (epiphytic) and in (endophytic) the needles) in our study areas in Alaska was investigated. The mycobiome of the white spruce needles was chosen as a proxy for the parasite infection rate by fungi and thus serves as a fitness parameter. For this purpose, all epiphytic and endophytic fungal species were analyzed by a metabarcoding analysis.
In article II, 48 trees of one study area at Alaska’s northern treeline (Brooks Range) were examined for differences in mycobiome due to genetic differentiation, phenotypic characteristics and / or habitat characteristics. The trees used for this study were sampled from two adjacent plots on a south-facing mountain slope with an elevation gradient from 875 to 950 meters above sea level. It could be shown that, in contrast to the trees genotype, the height above sea level, the mountain slope, as well as the height and age of the trees have a significant impact on the mycobiome. The genetic differentiation between the tree individuals, however, showed no significant effect.
Based on article II we examined the mycobiome composition of a total of 96 trees in 2 plots (16 trees each) at three sites in Alaska over a distance of 500 kilometers. Additionally, we sampled needles of two different ages for each tree (current year and three years old needles) summing up to 192 samples in total. The incentive of this study (article III) was to investigate the influence of origin and age of spruce needles on their mycobiome and if there is a genetic predisposition that is related to the fungal species community. In addition, the sampling design was improved by collecting needles from all four orientations (North, South, East and West) and sampling trees at a standardized distance to each other to avoid systematic errors. Comparable to article II the influence of the trees genetics on the species community of the epiphytic and endophytic fungi of the white spruce needles seems to be very unlikely. In contrast, a significant influence of the geographic origin and the needle age on the species structure of the needle inhabiting fungal species was found. The phenotypic tree traits height and dbh (diameter at breast height) had only minor influence and did in fact explain less than 2% of the mycobiome variance. Using Illumina sequencing, 10.2 million reads from the nucleotide sequence between the internal transcribed spacer (ITS) genes could be obtained, which yielded in 1575 ribotypes (called operational taxonomic unit, OTU) for the fungi. These were compared with a reference database to compare and assign them to known fungal species. For example, 942 OTUs with >95% similarity could be identified as known species, with 1975 samples identified on genus level and 2683 when determined to family level. The most pronounced difference between the two studies (article II and III) were due to the fungal species of the class of Pucciniomycetes, more specifically the genus Chrysomyxa which belongs to the rust fungi and is plant pathogenic. In the study of article II (sampling in 2012), Pucciniomycetes accounted for only a minor portion of the assigned DNA sequences. In the second study (article III, sampling in 2015) they accounted for more than half of all basidiomycetes found, which in turn contain 20.0% of all DNA sequences, the second largest phylum found beside Ascomycetes (51.4%).
Myxomycetes or Myxogastria (supergroup Amoebozoa) are one of several Protistean groups dispersing via airborne spores. The model organism for the group, so far exclusively studied in a laboratory environment, is Physarum polycephalum. Here, molecular evolution, distribution and the ecology of spores dispersal was investigated for the non-model species Physarum albescens. This nivicolous myxomycete fruits with snow melt in most mountain ranges of the northern hemisphere and disperses via spherical, dark-colored and melanin-rich spores. Fruit body development and subsequent spore dispersal occurs within a short time window of a few days. At this time, the fruiting plasmodium is fully exposed to the harsh environment if the protecting snow melts away. The spores, with a diameter of 10–13 µm of the typical size for myxomycetes, can potentially reach all suitable habitats worldwide, which led to the assumption that not only Ph. albescens but most myxomycete species should be ubiquitously distributed over the world.
In the first part of this study (article 1), the question was, if spore dispersal can realize a gene flow sufficient to meet the above-mentioned assumption. A total of 324 accessions of Ph. albescens, collected all over the northern hemisphere, was sequenced for 1-3 genetic markers (SSU, EF1A, COI), and 98 specimens were further analyzed using the genotyping by sequencing technique. As a result, at least 18 reproductively isolated units, which can be seen as cryptic biological species, emerged as phylogroups in a three-gene phylogeny, but as well in a SNP-based phylogeny and were confirmed by a recombination analysis between the three markers. However, this evolutive radiation is not simply caused by geographic fragmentation due to low dispersal capability: within a certain region, multiple phylogroups coexisted next to each other, although some appeared to be regional endemics. Most likely, mutations in mating-type genes, as shown to exist for the cultivable Ph. polycephalum, are the main drivers of speciation. This challenges the hypothesis of ubiquitous distribution of Ph. albescens and corroborates the results of the few available studies for other myxomycete species. In addition, groups of clonal specimens, mostly but not always restricted to a certain slope or valley indicated that sexual and asexual reproduction coexists in the natural populations of Ph. albescens.
In the second part (articles 2), the fundamental niche for Ph. albescens was described using all available records for the species. The resulting set of 537 unique occurrence points was subjected to a correlative spatial approach using the software MaxEnt. In dependence on the predictor variables three species distribution models emerged which differed only in details. The first consisted of only 19 bioclimatic variables and an elevation map from the WorldClim dataset. The second was corrected for pseudo-absences resulting from missing survey activities, and the third was expanded with an additional categorical environment variable on snow cover. High mean AUC (area under the curve) values above 0.97 could be reached with all three models. Variables for snow cover, precipitation of the coldest quarter (of the year), and elevation correlated highly to predict the distribution of Ph. albescens. Only in mid-northern latitudes, elevation alone was a good predictor, but it would cause false-positive predictions in arid mountain ranges and failed to explain occurrence in lowland sites at higher latitudes. Mountains in humid climates showed the highest incidences, confirming recent studies that long-lasting snow covers combined with mild summers are crucial for the ecological guild of nivicolous myxomycetes, with Ph. albescens as a typical species.
Spore size is crucial for dispersal ability and should thus be a character under strong selection. In addition, spores carrying two nuclei with opposite mating types should have a colonization advantage. This was the hypothesis for the last part of this study (articles 3 and 4), which investigated this trait in a quantitative manner. This required a method to analyze thousands of spores automatically (article 3) and with high precision for size and the number of nuclei enclosed. Human errors should be excluded, to reveal even subtle differences in the resulting spore size distributions. Two challenges had to be met for this approach. First, a preparation technique was developed to reduce false segmentations due to overlaying spores by aligning spores on one common plane with a high-frequency vibration device. Second, the segmentation process was automated to allow separating spores that are densely packed in the respective images. A machine learning algorithm was set up and trained to reliable identify and measure dark-colored spores. The technique produced consistent results with high accuracy, and the large number of spores allowed to compile spore size distributions, to check for the constancy of this character, which is impossible with manual measurements limited to low numbers.
The resulting spore size distributions, obtained from over 80 specimens (article 4), were mostly narrow, which is in accordance with our hypothesis. Spore size was as well fairly constant within fructifications from one colony. However, mean spore size within different accessions of Ph. albescens showed large variation (ca. 10%, a range often indicated to key out different morphospecies of myxomycetes), and this was explained only by a minor part with differences between biospecies. Not much smaller (8%) was the variation within a group of clonal specimens collected within 25 m distance. This points to a strong influence of environmental factors even at a micro spatial scale, perhaps caused by microclimatic differences and high phenotypic plasticity for spore size. The influence of large-scale covariates like altitude or latitude was negligible. However, spore size correlated with the variance in this trait, indicating that oversized spores may be caused by detrimental environmental conditions. Two aberrations in spore development were found: First, a few specimens showed a multimodal distribution for spore size with two or even three discernible spore populations. The estimated volumes of those populations correspond to a multiple of the first and most abundant conspicuous spore size population. Second, not all spores were uninucleate as to be expected for meiotic products. This was revealed by fluorescence signals from staining the same spores with DAPI, with a second machine learning algorithm trained to identify the nuclei in a spore. A few specimens showed a significant proportion of binucleated spores in the size range of normal-sized ones, and these specimens were not the ones with multimodal spore size distributions. This indicates that the negative impacts (inbreeding) of multinucleate spores should outweigh a possible colonization advantage and is in accordance with the high genetic diversity found in the worldwide population of Ph. albescens, indicating predominantly sexual reproduction in wild populations of myxomycetes.
Drainage has commonly been a pre-requisite for the productive use of peatlands. The biased focus on agriculture, forestry and peat extraction has long ignored the destructive effects of drainage and the successive degradation of ecosystem functions of wet peatlands. Accelerated by the climate crisis, the finite nature of drainage-based peatland use is increasingly recognised. Consequently, productive land use options for wet or rewetted peatlands (paludiculture) are required as sustainable alternatives. A wide range of paludiculture plants and options of biomass utilisation are identified as suitable and promising. Despite the growing interest, experiences with and research on the economic viability of paludiculture are still rare.
This thesis addresses the lack of knowledge on paludiculture in terms of practical feasibility, costs and benefits at the farm level, market prospects and framework conditions. I selected the two currently most advanced paludicultural practices in Europe: a) Harvesting natural reed beds as a traditional ‘low-input’ paludiculture, i. e. the utilisation of existing ‘wild’ vegetation stands; b) ‘Sphagnum farming’ as a novel ‘high-input’ paludiculture including stand establishment and water management required for the active transformation from drainage-based peatland use to paludiculture. In both cases, I investigate three different biomass utilisation avenues. This thesis adds to the fields of problem-driven sustainability and land-use science. Procedures and costs of paludiculture were studied in transdisciplinary research projects in close cooperation with practitioners. Due to the novelty of the topic, I put special emphasis on the triangulation of methods and data sources: pilot trials, field measurements, semi-structured expert interviews, structured questionnaires, secondary data from trade statistics and literature. To account for uncertainty related to costs and revenues, I conduct stochastic scenario analysis (Monte Carlo simulation) for the extended contribution margin accounting of harvesting reeds and sensitivity analysis for the investment appraisal of Sphagnum farming.
Paludiculture on fens: harvesting reeds
Paper I investigates harvesting procedures for reed-dominated (Phragmites australis) vegetation stands. In many European countries special-purpose tracked machinery is applied for large-scale conservation management and the commercial harvest of thatching reed. Stochastic scenario analysis reveals a wide range of possible economic outcomes (ca. € -1000 to € 1500 ha-1 a-1) and identifies material use of reed superior to its use as a source of energy. Winter harvest of high-quality thatching reed in bundles is the most profitable option. Winter harvest of bales for direct combustion is suitable for low-quality stands and has a limited risk of loss. In the case of summer harvest, revenues for green chaff for biogas production cannot cover harvesting costs but non-market income via subsidies and agri-environmental payments may ensure profitability. While biomass for energy generation is limited to a local market, thatching reed is traded as an international commodity. The market situation for thatching reed is investigated for Europe (Paper II) and Germany (Paper III). The major reed consuming countries in Western Europe (Netherlands, Germany, UK, Denmark) rely on imports of up to 85 % of the national consumption, with reed being imported from Eastern and Southern Europe and since 2005 also from China. The total market volume for reed for thatching in Northern Germany is estimated with 3 ± 0.8 million bundles of reed with a monetary value at sales prices of € 11.6 ± 2.8 million. Most of the thatchers (70 %) did not promote reed of regional origin to their customers due to insufficient availability in the first place and a lack in quality as second reason. The cultivation of reed in paludiculture may improve quantity and quality of domestic thatching reed. An area of 6000 ± 1600 ha with an average yield of 500 bundles per hectare would allow covering the current total demand of 3 million bundles of the German thatching reed market (Paper III).
Paludiculture on bogs: Sphagnum farming
Sphagnum farming provides an alternative to peatland degradation in two ways: Firstly, Sphagnum mosses can be cultivated as new agricultural crops on rewetted peatlands. Secondly, the produced Sphagnum biomass is a high-quality raw material suitable to replace peat in horticultural growing media (Paper V). Pilot trials have demonstrated the practical feasibility of establishing Sphagnum cultures on former bog grassland, cut-over bogs and mats floating on acidic waters bodies; Paper IV compares for the three types of production sites the specific procedures, costs and area potential in Germany. Water-based Sphagnum farming is not recommended for large-scale implementation due to highest establishment costs, major cultivation risks and limited area potential. For soil-based Sphagnum farming, the most important cost positions were Sphagnum shoots to set up pilots, investment for water management and regular weed management. Bog grassland has the highest area potential, i. e. 90,000 ha in NW Germany. Paper V assesses the profitability of Sphagnum farming on former bog grassland based on extrapolating five years of field experience data (establishment ņ management ņ harvest) to a total cultivation time of twenty years. Cultivating Sphagnum biomass as founder material for Sphagnum farming or restoration was profitable even in pessimistic scenarios with high costs, high bulk density and low yields. Selling Sphagnum for orchid production was economically viable in the case of medium to high yields with a low bulk density. Cost-covering prices for Sphagnum biomass substituting peat seem achievable if end consumers pay a surcharge of 10 % on the peat-free cultivated horticultural end-product. An area of 35,000 ha of Sphagnum farming suffices to meet the annual demand of the German growing media industry for slightly decomposed Sphagnum peat.
Framework conditions affecting feasibility of paludiculture
The relation of revenues from selling biomass to its production costs is an important piece of the paludiculture feasibility puzzle. Further aspects effecting the economic viability and competitiveness of paludiculture encompass the market demand, the availability of mature technology, legal restrictions, the eligibility for agricultural subsidies, a remuneration of external benefits and the opportunity costs of present farming activities (Paper I, V). Legal and policy regulations are of major importance for land use decisions on peatlands – both for keeping up drainage and for shifting to paludiculture.
Conclusion and Outlook
This thesis provides a first assessment of the costs and profitability of large-scale harvesting of reeds and Sphagnum farming based on real-life data. The paludicultural practices investigated may be a solution for a minor share of the more than 1 million ha of peatlands drained for agriculture in Germany. Future research should also address other biomass utilisation options and other crops. Large-scale pilots are required to improve technical maturity of procedures and machinery, gather reliable data to replace assumptions on costs and revenues and study long-term effects on economics and ecosystem services. The micro-economic perspective needs to be complemented by the societal perspective quantifying and monetising external effects of peatland restoration, paludiculture and drainage-based peatland use. There is a high need for intensified research, large-scale implementation and accelerated adaption of the policy and legal framework to develop paludiculture as an economically viable option for degraded peatlands.
Durch zymografische Untersuchungen und Massenspektrometrie (MS) wurden neun Proteasen vom Subtilisin-Typ im Wurzelexsudat von Nicotiana tabacum identifiziert. Ein Peptid-Antikörper wurde produziert, der die affinitätschromatografische Anreicherung einer tobacco root exuded subtilase (TREXS, XP_016501597.1) und zweier Isoformen sowie eines Peroxidase-artigen und eines SERK2-artigen Proteins ermöglichte. Basierend auf dem Subtilase-EST, der in der MS identifiziert worden war, wurde die full-length cDNA von TREXS durch 5'RACE und 3'RACE sequenziert und die gDNA kloniert. Das intronfreie TREXS-Gen codiert eine 756 Aminosäuren lange Subtilase mit Signalpeptid, I9-Inhibitordomäne, PA- und Fn-III-artiger Domäne. Der Nachweis von TREXS-mRNA in Blattgewebe zeigte, dass TREXS nicht exklusiv auf Wurzeln beschränkt ist. Phylogenetische Analysen zeigten, dass SDD1 die ähnlichste Subtilase aus A. thaliana zu TREXS ist. Mit großer Wahrscheinlichkeit ist TREXS jedoch nicht das Ortholog zu SDD1, weil zum einen strukturähnlichere Subtilasen zu SDD1 in Tabak existieren und zum anderen SDD1 an der Ausprägung von Stomata in der Blattepidermis beteiligt ist, TREXS hingegen im Wurzelexsudat vorkommt. Das
MS-identifizierte SERK2-artige Protein, das bei der Peptid-Antikörper-Affinitätschromatografie zusammen mit TREXS angereichert wurde, ist Kandidat als Substrat für TREXS, weil es potenziell durch IgG–TREXS–SERK2-like-Interaktion co-angereinigt wurde, die in-silico docking-Vorhersagen zwischen den modellierten Molekülen von TREXS und SERK2-like einen proteolytisch relevanten Bindungszustand vorhersagt und es strukturelle Ähnlichkeit mit LRP, einem bekannten Substrat der Subtilase P69C, hat. Die transiente Expression rekombinanter TREXS in N. benthamiana war möglich, zeigte sich jedoch kritisch gegenüber C- und N-terminal fusionierten Anhängen: Transiente Transformation mit TREXS oder TREXS:Strep-tag führte zu proteolytisch aktivem Protein. Jedoch war der C-terminale Strep-tag nicht funktionell. Längere C-terminale Anhänge und auch TREXS-Mutanten mit inaktiviertem katalytischen Zentrum erbrachten kein Genprodukt. C-terminales GFP erbrachte – auch bei mutiertem katalytischen Zentrum – stets nur den GFP-Anteil des Fusionsproteins.
The rapid anthropogenic climate change that is projected for the 21st century is predicted to have severe impacts on ecosystems and on the provision of ecosystem services. With respect to the longevity of trees, forestry in particular has to adapt now to future climate change. This requires profound multidisciplinary knowledge on the direct and indirect climate sensitivity of forest ecosystems on various spatial scales. Predictions on growth declines due to increasing drought exposition during climate change are widely recognized for European beech (Fagus sylvatica L.), which is the major forest tree in European temperate deciduous forests. However, research from other continents or other biomes has shown that winter climate change may also affect forest growth dynamics due to declining snow cover and increased soil cooling. So far, this winter cold sensitivity is largely unexplored in Europe. Thus, particularly focussing on forest growth dynamics and winter cold sensitivity, the goal of this PhD-project was to explore how climate sensitivity of forest ecosystems differs regionally. By doing so, the project aimed to deliver insights about possibilities and limits of upscaling regional knowledge to a global understanding of climate sensitivity. To achieve these goals, this PhD-project integrated five studies (Manuscripts 1–5) that investigated the climate sensitivity of biogeochemical cycles, plant species composition in forests, and forest growth dynamics across spatial scales. In particular, a large-scale gradient-design field experiment simulated the influence of winter climate change on forest ecosystems by snow cover and soil temperature manipulations (Manuscript 1). This study indicated that soil cooling and decreased root nutrient uptake may indirectly reduce growth of adult forest trees. Moreover, this study indicated uniform ecological sensitivity to soil temperature changes across sites along a large winter temperature gradient (ΔT = 4 K across 500 km), irrespective of the site-specific history of snow cover conditions, which motivates upscaling from local winter climate change studies to the regional scale. Although regional climate drives growth of adult forest trees, local factors, such as site-specific edaphic conditions, might control plants in the forest understory. This assumption was tested by mapping the forest understory composition along the same winter temperature gradient as introduced above (Manuscript 2). Across sites, this study found that edaphic conditions explained the spatial turnover in the forest understory composition more than climate, which might moderate direct climate change impacts on the forest understory composition. However, edaphic conditions, forest structure, and climate are linked by triangular interactions. Thus, climate change might still indirectly affect the forest vegetation dynamics. Moreover, a dendroecological study focussed on the same winter temperature gradient from central to cold-marginal beech populations as above in order to identify gradual changes in summer drought and winter cold sensitivity in tree growth (Manuscript 3). Towards the cold distribution margin, the influence of drought on tree growth gradually decreased, while growth reductions were increasingly related to winter cold due to harsher winter climate. By a large-scale dendroecological network study assessed the relationship of growth dynamics to climate and reproductive effort in beech forests across Europe (Manuscript 4). Indeed, this study found the general pattern across the distribution range of beech that high temperature controlled growth indirectly via resource allocation to reproduction. However, the strong, direct drought signal that could be generally detected from dry-marginal to central populations vanished towards the cold-marginal populations, where the more focussed study of Manuscript 3 identified a stronger relationship of tree growth to winter cold. Further extending the scope of this PhD-thesis to global scales, litter decomposition rates were assessed across biomes (Manuscript 5). This study found a robust relationship between climate and decomposition rates, but it also demonstrated large within-biome variability on a local scale. These local scale differences might depend on habitat conditions that, in turn, could be modulated by climate change, which calls for a better exploration of indirect climate sensitivity. In conclusion, this PhD-thesis highlighted that multidisciplinary research can advance the understanding of ecological interactions in forest ecosystems under changing climate scenarios. In this PhD-project, a winter climate change experiment, where site-representative target trees were selected by means of dendroecology, contributed to a mechanistic understanding of winter cold sensitivity in forest growth dynamics. Dendroecological investigations then put the findings in a broader temporal and spatial context by describing local climate sensitivity of tree growth on different spatial scales. This thesis further shows that global generalizations about the relationship of climate and ecological processes in ecosystem models have to be critically reviewed for the need of local and regional adjustment because these processes might experience considerable regional- or local-scale variation. However, this thesis reports uniform sensitivity of ecological processes to altered winter soil temperature regimes across a large winter temperature gradient. Thus, upscaling from insights of previous winter climate change experiments to regional scales is encouraged.
Abstract
Higher biodiversity can stabilize the productivity and functioning of grassland communities when subjected to extreme climatic events. The positive biodiversity–stability relationship emerges via increased resistance and/or recovery to these events. However, invader presence might disrupt this diversity–stability relationship by altering biotic interactions. Investigating such disruptions is important given that invasion by non‐native species and extreme climatic events are expected to increase in the future due to anthropogenic pressure. Here we present one of the first multisite invader × biodiversity × drought manipulation experiment to examine combined effects of biodiversity and invasion on drought resistance and recovery at three semi‐natural grassland sites across Europe. The stability of biomass production to an extreme drought manipulation (100% rainfall reduction; BE: 88 days, BG: 85 days, DE: 76 days) was quantified in field mesocosms with a richness gradient of 1, 3, and 6 species and three invasion treatments (no invader, Lupinus polyphyllus, Senecio inaequidens). Our results suggest that biodiversity stabilized community productivity by increasing the ability of native species to recover from extreme drought events. However, invader presence turned the positive and stabilizing effects of diversity on native species recovery into a neutral relationship. This effect was independent of the two invader's own capacity to recover from an extreme drought event. In summary, we found that invader presence may disrupt how native community interactions lead to stability of ecosystems in response to extreme climatic events. Consequently, the interaction of three global change drivers, climate extremes, diversity decline, and invasive species, may exacerbate their effects on ecosystem functioning.
Understanding the effects of temperature and moisture on radial growth is vital for assessing the impacts of climate change on carbon and water cycles. However, studies observing growth at sub-daily temporal scales remain scarce.
We analysed sub-daily growth dynamics and its climatic drivers recorded by point dendrometers for 35 trees of three temperate broadleaved species during the years 2015–2020. We isolated irreversible growth driven by cambial activity from the dendrometer records. Next, we compared the intra-annual growth patterns among species and delimited their climatic optima.
The growth of all species peaked at air temperatures between 12 and 16°C and vapour pressure deficit (VPD) below 0.1 kPa. Acer pseudoplatanus and Fagus sylvatica, both diffuse-porous, sustained growth under suboptimal VPD. Ring-porous Quercus robur experienced a steep decline of growth rates with reduced air humidity. This resulted in multiple irregular growth peaks of Q. robur during the year. By contrast, the growth patterns of the diffuse-porous species were always right-skewed unimodal with a peak in June between day of the year 150–170.
Intra-annual growth patterns are shaped more by VPD than temperature. The different sensitivity of radial growth to VPD is responsible for unimodal growth patterns in both diffuse-porous species and multimodal growth pattern in Q. robur.
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.
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.
Individual white spruce (Picea glauca (Moench) Voss) growth limitations at treelines in Alaska
(2018)
White spruce (Picea glauca (Moench) Voss) is one of the most common conifers in Alaska and various treelines mark the species distribution range. Because treelines positions are driven by climate and because climate change is estimated to be strongest in northern latitudes, treeline shifts appear likely. However, species range shifts depend on various species parameters, probably most importantly on phenotypic plasticity, genetic adaptation
and dispersal. Due to their long generation cycles and their immobility, trees evolved to endure a wide variety of climatic conditions. In most locations, interannual climate variability is larger than the expected climate change until 2100. Thus treeline position is typically thought of as the integrated effect of multiple years and to lag behind gradual climate change by several decades. Past dendrochronological studies revealed that growth of white spruce in Alaska can be limited by several climatic variables, in particular water stress and low temperatures. Depending on how the intensity of climate warming, this could result in a leading range edge at treelines limited by low temperatures and trailing treelines where soil moisture is or becomes most limiting. Climate-growth correlations are the dendrochronological version of reaction norms and describe the relationship between an environmental variable and traits like tree-ring parameters (e.g. ring width, wood density, wood anatomy). These correlations can be used to explore potential effects of climate change on a target species. However, it is known that individuals differ with respect to multiple variables like size, age, microsite conditions, competition status or their genome. Such individual differences could be important because they can modulate climate-growth relationships and consequently also range shifts and growth trends. Removing individual differences by averaging tree-ring parameters of many individuals into site chronologies could be an oversimplification that might bias estimates of future white spruce performance. Population dynamics that emerge from the interactions of individuals (e.g. competition) and the range of reactions to the same environmental drivers can only be studied via individual tree analyses. Consequently, this thesis focuses on factors that might alter individual white spruce’ climate sensitivity and methods to assess such effects. In particular, the research articles included explore three topics:
1. First, clones were identified via microsatellites and high-frequency climate signals of clones were compared to that of non-clonal individuals. Clonal and non-clonal individuals showed similar high-frequency climate signals which allows to use clonal and non-clonal individuals to construct mean site chronologies. However, clones were more frequently found under the harsher environmental conditions at the treelines which could be of interest for the species survival strategy at alpine treelines and is further explored in the associated RESPONSE project A5 by David Würth.
2. In the second article, methods for the exploration and visualization of individual-tree differences in climate sensitivity are described. These methods represent a toolbox to explore causes for the variety of different climate sensitivities found in individual
trees at the same site. Though, overlaying gradients of multiple factors like temperature, tree density and/or tree height can make it difficult to attribute a single cause to the range of reaction norms (climate growth correlations).
3. Lastly, the third article attempts to disentangle the effect of age and size on climate-growth correlations. Multiple past studies found that trees of different Ages responded differently to climatic drivers. In contrast, other studies found that trees do not age like many other organisms. Age and size of a trees are roughly correlated, though there are large differences in the growth rate of trees, which can lead to smaller trees that are older than taller trees. Consequently, age is an imperfect Proxy for size and in contrast to age, size has been shown to affect wood anatomy and thus tree physiology. The article compares two tree-age methods and one tree-size method based on cumulative ring width. In line with previous research on aging and Wood anatomy, tree size appeared to be the best predictor to explain ontogenetic changes in white spruce’ climate sensitivity. In particular, tallest trees exhibited strongest correlations with water stress in previous year July. In conclusion, this thesis is about factors that can alter climate-growth relationships (reaction norms) of white spruce. The results emphasize that interactions between climate variables and other factors like tree size or competition status are important for estimates of future tree growth and potential treeline shifts. In line with previous studies on white spruce in Alaska, the results of this thesis underline the importance of water stress for white spruce.
Individuals that are taller and that have more competitors for water appear to be most susceptible to the potentially drier future climate in Alaska. While tree ring based growth trends estimates of white spruce are difficult to derive due to multiple overlaying low frequency (>10 years) signals, all investigated treeline sites showed highest growth at the treeline edge. This could indicate expanding range edges. However, a potential bottleneck for treeline advances and retreats could be seedling establishment, which should be explored in more detail in the future.
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.
Water Consumption of Agriculture and Natural Ecosystems along the Ili River in China and Kazakhstan
(2017)
Pollen productivity estimates (PPEs) are a key parameter for quantitative land-cover reconstructions from pollen data. PPEs are commonly estimated using modern pollen-vegetation data sets and the extended R-value (ERV) model. Prominent discrepancies in the existing studies question the reliability of the approach. We here propose an implementation of the ERV model in the R environment for statistical computing, which allows for simplified application and testing. Using simulated pollen-vegetation data sets, we explore sensitivity of ERV application to (1) number of sites, (2) vegetation structure, (3) basin size, (4) noise in the data, and (5) dispersal model selection. The simulations show that noise in the (pollen) data and dispersal model selection are critical factors in ERV application. Pollen count errors imply prominent PPE errors mainly for taxa with low counts, usually low pollen producers. Applied with an unsuited dispersal model, ERV tends to produce wrong PPEs for additional taxa. In a comparison of the still widely applied Prentice model and a Lagrangian stochastic model (LSM), errors are highest for taxa with high and low fall speed of pollen. The errors reflect the too high influence of fall speed in the Prentice model. ERV studies often use local scale pollen data from for example, moss polsters. Describing pollen dispersal on his local scale is particularly complex due to a range of disturbing factors, including differential release height. Considering the importance of the dispersal model in the approach, and the very large uncertainties in dispersal on short distance, we advise to carry out ERV studies with pollen data from open areas or basins that lack local pollen deposition of the taxa of interest.