Open Access

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.

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.

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.

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 Root phenology influences the timing of plant resource acquisition and carbon fluxes into the soil. This is particularly important in fen peatlands, in which peat is primarily formed by roots and rhizomes of vascular plants. However, most fens in Central Europe are drained for agriculture, leading to large carbon losses, and further threatened by increasing frequency and intensity of droughts. Rewetting fens aims to restore the original carbon sink, but how root phenology is affected by drainage and rewetting is largely unknown. We monitored root phenology with minirhizotrons in drained and rewetted fens (alder forest, percolation fen and coastal fen) as well as its soil temperature and water table depth during the 2018 drought. For each fen type, we studied a drained site and a site that was rewetted ~25 years ago, while all the sites studied had been drained for almost a century. Overall, the growing season was longer with rewetting, allowing roots to grow over a longer period in the year and have a higher root production than under drainage. With increasing depth, the growing season shifted to later in time but remained a similar length, and the relative importance of soil temperature for root length changes increased with soil depth. Synthesis and applications. Rewetting extended the growing season of roots, highlighting the importance of phenology in explaining root productivity in peatlands. A longer growing season allows a longer period of carbon sequestration in form of root biomass and promotes the peatlands' carbon sink function, especially through longer growth in deep soil layers. Thus, management practices that focus on rewetting peatland ecosystems are necessary to maintain their function as carbon sinks, particularly under drought conditions, and are a top priority to reduce carbon emissions and address climate change.