Stefan Georg Michalski

Invasive plant species present a growing ecological and economic challenge, and often adapt rapidly to their novel environments through complex demographic and evolutionary processes. Invasion genomics offers powerful tools to disentangle these processes, but most studies rely on geographically narrow sampling across native and non‐native ranges. Erigeron canadensis is a cosmopolitan weed native to North America that has successfully invaded diverse climates worldwide. We used double‐digest restriction site‐associated DNA sequencing (ddRADseq) to investigate the genetic diversity and structure of 280 E. canadensis populations across the Northern Hemisphere. We found that native and non‐native populations maintained comparable genetic diversity. Population structure analyses revealed four genetic clusters that were mainly differentiated along latitudinal and aridity gradients. However, one cluster was strongly overrepresented in the non‐native compared to the native range. In the native range, genetic differentiation was shaped by spatial and environmental gradients, while in non‐native regions human‐mediated dispersal and repeated introductions disrupted environmentally driven genetic structure. Migration network analyses revealed limited intercontinental connectivity and a possible role of long‐distance dispersal in within‐range expansions. Genomic offset analyses showed that genotype‐environment mismatches in non‐native populations associated with reduced growth and reproduction. Together, our results indicate that the invasion dynamics of E. canadensis were driven by multiple introductions, population admixture, and lineage sorting, while some genotypes contributed disproportionately to the spread of this invader. The presence of apparent maladaptation suggests that even long‐established invaders may still be evolving in response to their novel environment, raising concerns about potential future expansions.

Regional seed sources are increasingly used in ecological restoration. Polyploid complexes, i.e. taxa comprising multiple ploidy levels, are often part of regional seed mixtures, where ploidy levels are often not distinguished. However, mixing ploidy levels may foster their hybridisation, severely reduce offspring fitness and disrupt existing patterns of the geographic distribution of individual ploidy levels. Furthermore, ploidy levels may represent distinct genetic lineages. Yet, the exact geographic distribution of the ploidy levels and their genetic differentiation are rarely known. Here, we focus on six polyploid complexes commonly used for the restoration of species‐rich grasslands. We present high‐resolution, national‐scale geographic distributions of their ploidy levels, test their association with environmental gradients and quantify genetic differentiation between ploidy levels. Ploidy levels within polyploid complexes were more differentiated than seed zones within individual ploidy levels. The abundance, spatial distribution and levels of sympatry versus parapatry of ploidy levels varied widely among polyploid complexes. Nevertheless, the spatial distribution of ploidy levels was always associated with environmental gradients. Mixed‐ploidy populations were generally rare. Campanula rotundifolia , Euphorbia cyparissias , and Pimpinella saxifraga showed regional parapatry of ploidy levels, whereas Achillea millefolium agg., Knautia arvensis , and Leucanthemum vulgare agg. showed rather sympatric distribution patterns. Diploid K. arvensis was very rare and potentially non‐native to Germany. Using these datasets as case studies, we present a management decision framework for polyploid complexes in seed zone‐based grassland restoration, requiring only cytotype distribution data that can be acquired at reasonable cost. The framework recommends four different per‐zone management options based on data availability, cytotype presence, distribution, and frequency. Synthesis and applications . Our decision framework enables seed producers and managers to take consistent action on the challenge of polyploid complexes in restoration. Different ploidy levels should not be mixed to avoid fitness losses. Depending on abundance and distribution, either the dominant ploidy level should be prioritised, or multiple ploidy levels need to be managed independently at the seed zone level.

Restoring temperate grasslands often necessitates the introduction of large quantities of seeds, a process that is regulated by seed transfer zones in many countries. These zones are commonly delineated based on abiotic factors. Consequently, it remains uncertain to what extent existing seed zones represent and thereby protect or erode the spatial distribution of genetic variation. Empirical data on the spatial genetic structure of grassland species are therefore essential to address this knowledge gap. Moreover, as seed zones are increasingly expected to provide genotypes pre‐adapted to climate change, such data can also inform predictions of maladaptation and support the identification of suitable donor populations. Here, we focus on Galium album , a widespread perennial grassland species, which we sampled systematically across Germany, with an average of one population per 25 × 25 km area. Based on 8348 SNP loci, we analyzed the population genetic structure using Bayesian clustering. We identified four spatially coherent genetic clusters, which explained 2.43% of genomic variation but showed little congruence with current seed zones. Yet, seed zones still capture a significant component of spatial genetic structure (1.92%), which is also reflected in a significant isolation by distance among zones. Seed transfer practices are increasingly challenged by climate change, shifting the adaptive requirements for populations. We performed a genotype–environment association analysis using redundancy analysis, and estimated the genomic offset, that is, the genomic change required to maintain the current genotype‐environment relationship under climate change. The genomic offset was generally moderate across Germany, even under a pessimistic climate scenario projected into the more distant future (SSP5‐8.5, 2081‐2100). For one of the few locations where the temporal genomic offset slightly exceeded a previously proposed threshold, we identified suitable donor regions harbouring potentially pre‐adapted genotypes for targeted assisted migration, both within the same and in adjacent zones.

Climate and land‐use change are key drivers of global change. Full‐factorial field experiments in which both drivers are manipulated are essential to understand and predict their potentially interactive effects on the structure and functioning of grassland ecosystems. Here, we present 8 years of data on grassland dynamics from the Global Change Experimental Facility in Central Germany. On large experimental plots, temperature and seasonal patterns of precipitation are manipulated by superimposing regional climate model projections onto background climate variability. Climate manipulation is factorially crossed with agricultural land‐use scenarios, including intensively used meadows and extensively used (i.e., low‐intensity) meadows and pastures. Inter‐annual variation of background climate during our study years was high, including three of the driest years on record for our region. The effects of this temporal variability far exceeded the effects of the experimentally imposed climate change on plant species diversity and productivity, especially in the intensively used grasslands sown with only a few grass cultivars. These changes in productivity and diversity in response to alterations in climate were due to immigrant species replacing the target forage cultivars. This shift from forage cultivars to immigrant species may impose additional economic costs in terms of a decreasing forage value and the need for more frequent management measures. In contrast, the extensively used grasslands showed weaker responses to both experimentally manipulated future climate and inter‐annual climate variability, suggesting that these diverse grasslands are more resistant to climate change than intensively used, species‐poor grasslands. We therefore conclude that a lower management intensity of agricultural grasslands, associated with a higher plant diversity, can stabilize primary productivity under climate change.

Climate and land-use change are key drivers of global change. Full-factorial field experiments in which both drivers are manipulated are essential to understand and predict their potentially interactive effects on the structure and functioning of grassland ecosystems. Here, we present eight years of data on grassland dynamics from the Global Change Experimental Facility (GCEF) in Central Germany. On large experimental plots, temperature and seasonal patterns of precipitation are manipulated by superimposing regional climate model projections onto background climate variability. Climate manipulation is factorially crossed with agricultural land-use scenarios, including intensively used meadows and extensively used (i.e. low-intensity) meadows and pastures. Inter-annual variation of background climate during our study years was high, including three of the driest years on record for our region. The effects of this temporal variability far exceeded the effects of the experimentally imposed climate change on plant species diversity and productivity, especially in the intensively used, species-poor grasslands. These changes in productivity and diversity in response to alterations in climate were due to immigrant species replacing the target forage cultivars. This shift from forage cultivars to immigrant species may impose additional economic costs in terms of a decreasing fodder value and the need for more frequent management measures. In contrast, the extensively used, species-rich grasslands showed weaker responses to both experimentally manipulated future climate and inter-annual climate variability, suggesting that these diverse grasslands are more resistant to climate change than intensively used, species-poor grasslands. We therefore conclude that an extensive management of agricultural grasslands, together with other measures to increase species diversity, can stabilize primary productivity under climate change.

For terrestrial plant communities, the increase in frequency and intensity of drought events is considered as one of the most severe consequences of climate change. While single‐species studies demonstrate that drought can lead to relatively rapid adaptive genetic changes, the evolutionary potential and constraints to selection need to be assessed in comparative approaches to draw more general conclusions. In a greenhouse experiment, we compare the phenotypic response and evolutionary potential of two co‐occurring grassland plant species, Bromus erectus and Trifolium pratense, in two environments differing in water availability. We quantified variation in functional traits and reproductive fitness in response to drought and compared multivariate genetic variance–covariance matrices and predicted evolutionary responses between species. Species showed different drought adaptation strategies, reflected in both their species‐specific phenotypic plasticity and predicted responses to selection indicating contrasting evolutionary potential under drought. In T. pratense we found evidence for stronger genetic constraints under drought compared to more favourable conditions, and for some traits plastic and predicted evolutionary responses to drought had opposing directions, likely limiting the potential for adaptive change. Our study contributes to a more detailed understanding of the evolutionary potential of species with different adaptive strategies in response to climate change and may help to inform future scenarios for semi‐natural grassland ecosystems.

The UN Decade on Ecosystem Restoration calls for upscaling restoration efforts, but many terrestrial restoration projects are constrained by seed availability. To overcome these constraints, wild plants are increasingly propagated on farms to produce seeds for restoration projects. During on-farm propagation, the plants face non-natural conditions with different selection pressures, and they might evolve adaptations to cultivation that parallel those of agricultural crops, which could be detrimental to restoration success. To test this, we compared traits of 19 species grown from wild-collected seeds to those from their farm-propagated offspring of up to four cultivation generations, produced by two European seed growers, in a common garden experiment. We found that some plants rapidly evolved across cultivated generations towards increased size and reproduction, lower within-species variability, and more synchronized flowering. In one species, we found evolution towards less seed shattering. These trait changes are typical signs of the crop domestication syndrome, and our study demonstrates that it can also occur during cultivation of wild plants, within only few cultivated generations. However, there was large variability between cultivation lineages, and the observed effect sizes were generally rather moderate, which suggests that the detected evolutionary changes are unlikely to compromise farm-propagated seeds for ecosystem restoration. To mitigate the potential negative effects of unintended selection, we recommend to limit the maximum number of generations the plants can be cultivated without replenishing the seed stock from new wild collections.