Timo Hellwig

1. Most plant species are genetically differentiated among populations, often reflected by phenotypic trait variation that corresponds to local adaptation. Yet the strength of local adaptation and heritable contribution to phenotypic traits vary across traits, species, and environments. Additionally, climate change is rapidly altering environmental conditions, and the climate may shift faster than populations can adapt or track the change via dispersal, resulting in adaptive lags. However, it remains unclear how widespread such adaptive lags are across plant species. 2. We focused on Hordeum murinum , an annual ruderal grass widespread in Europe. We combined continental-scale in situ measurements of 2070 plants across 207 populations with common garden experiments across two contrasting climates and two soil types to disentangle heritable variation from phenotypic plasticity and assess potential adaptive lags under climate change. 3. We found that heritable variation was pronounced in developmental traits, particularly flowering time and plant height, while seed weight, reproductive investment and SLA showed intermediate heritable contribution, and flag leaf area and total biomass were primarily plastic. Heritable trait variation was strongly associated with temperature at the populations’ origin, and trait clines were consistent with in situ patterns, suggesting that temperature is the main driver of genetic differentiation in H. murinum . However, we detected that fitness peaked in populations originating from warmer climates, indicating that evolutionary responses may not keep pace with rapid environmental shifts. 4. Synthesis: Our results highlight that H. murinum harbors substantial heritable variation, shaped primarily by temperature. However, the pace of evolutionary change may be insufficient to track ongoing climate change, leaving populations potentially vulnerable to future environmental conditions.

SUMMARY: Diploid and allopolyploid relatives often differ in their responses to stressful or variable environments, but it remains unclear whether this is reflected in greater reproductive stability in such conditions, and whether any such advantage is associated with greater canalisation or plasticity of morphological and developmental traits or a more extensive transcriptional response. We tested this in the annual grass Hordeum murinum by comparing the reproductive performance, phenotypic responses, and transcriptomic responses of diploid and allotetraploid H. murinum subspecies under control and elevated temperature conditions. Gene‐level nucleotide diversity was higher in the diploid ssp. glaucum than in either subgenome of the allotetraploid ssp. murinum , whereas divergence was greatest between the two subgenomes of the allotetraploid. Relative to ssp. glaucum , ssp. murinum altered expression in a larger proportion of its analysed transcriptome (10% versus 8%), spanned more enriched functional categories (36 versus 19), and showed pronounced subgenome‐specific contributions to the response. In addition, 702 of 11 106 homeolog pairs showed temperature‐dependent shifts in expression bias despite the absence of genome‐wide dominance of either subgenome. By contrast, phenotypic responses were largely similar between subspecies. Although ssp. glaucum and ssp. murinum differed in phenotype, especially in phenology, temperature explained more phenotypic variation than subspecies and reduced reproductive biomass by 42% in ssp. glaucum and 47% in ssp. murinum . Overall, ssp. murinum showed neither greater plasticity nor better maintenance of reproductive performance. Thus, compared with diploid H. murinum , allopolyploid H. murinum showed broader transcriptional deployment under elevated temperature, but not greater reproductive stability or clear differences in the plasticity of morphological and developmental traits. These results point to a decoupling of trait and molecular differentiation from fitness under elevated temperature, suggesting that the allotetraploid's altered transcriptional response may represent an alternative route to maintaining fitness comparable to that of the diploid rather than a reproductive advantage.

Background and Aims: Plant functional traits link environmental conditions to plant performance and adaptation. Growing evidence suggests that intraspecific trait variation can be as important as differences between species, yet large intraspecific studies of in situ variation remain rare. Most studies have focused on plant morphological traits, whereas the concentrations of elemental nutrients in seeds have received much less attention so far. Methods: We conducted a large-scale in situ study of the widespread annual ruderal grass Hordeum murinum. We sampled 2070 individuals from 207 populations across a large part of its native range in Europe and North Africa. We measured seed ripening phenology and growth-related traits in situ and analysed concentrations of elemental nutrients in the seeds. Key Results: We found that H. murinum grew larger, produced seeds later and had heavier seeds in colder and wetter regions. Plants growing in denser vegetation were taller and produced heavier seeds but formed fewer spikes. Concentrations of elemental nutrients in the seed generally declined with seed weight and were driven primarily by climatic variables, whereas soil conditions had only minor effects on plant traits and seed nutrients. Population identity explained a substantial proportion of trait variation, indicating a possible genetic component. Conclusions: Our findings provide a comprehensive view of how H. murinum responds to environmental gradients across its European distribution. Climatic variables, particularly temperature, are key drivers of reproductive timing and concentrations of elemental nutrients in the seed, whereas local environmental conditions, such as biotic pressures, are more important for growth-related traits. Together, these patterns indicate that H. murinum modulates its growth and reproductive investment along environmental gradients, balancing phenology, stress tolerance and limited competitive capacity.

Summary · There is growing interest in developing perennial cereal crops for sustainable production, yet key differences in trait syndromes between annual and perennial grasses and their influence on environmental adaptation remain poorly understood. · We measured 25 traits in 16 annual and perennial Hordeum species (45 accessions), including barley, grown over three seasons in a common garden. Using a phylogenetic framework and repeated transitions between annual and perennial forms, we (i) identified traits distinguishing these life strategies and (ii) tested how they relate to climate at the accessions' origins. · Wild and cultivated barley are distinguished within the Hordeum clade by high growth rates and large organs, which may have predisposed wild barley to domestication. Annual and perennial accessions differed in resource allocation: annuals had higher harvest index and leaf and grain nitrogen, while perennials produced carbon-rich tissues and sustained vegetative growth. Seasonal temperature variation shaped trait syndromes: annual traits aligned with temperature in the driest quarter, reflecting selection under terminal stress, while perennial traits correlated with temperature in the wettest quarter, the main growth phase shaping long-term performance and survival. · We provide important information on traits and climate adaptations underlying perennial persistence and annual resource strategies, relevant for developing perennial cereal crops.

Plant functional traits link environmental conditions to plant performance and adaptation. Growing evidence shows that in-situ intraspecific trait variation can be as important as differences between species, yet large intraspecific datasets measured in situ are rare. While most studies focused on plant morphological traits, contents of elemental nutrients in the seeds received much less attention so far. We conducted a large-scale in-situ study of the widespread ruderal grass Hordeum murinum . We sampled 2070 individuals from 207 populations from a large part of the native range in Europe and Northern Africa. In-situ, we measured seed ripening phenology and morphological traits, and analyzed the content of elemental nutrients in the seeds. We found that Hordeum murinum grew larger, produced seeds later, and had heavier seeds in colder and wetter areas. Plants in denser vegetation were taller with heavier seeds but formed fewer spikes. Seed nutrient content generally declined with seed weight and was mainly driven by climate. Soil conditions had only minor effects on plant traits and seed nutrients. Population identity explained much of the variation, indicating a possible genetic component. Synthesis : Our findings provide a comprehensive view of Hordeum murinum responding to environmental gradients across its European distribution. Climatic variables, especially temperature, are key drivers for reproductive success and seed nutrient content, while local environments, such as biotic pressures, are more critical for growth-related traits. These patterns indicate that H. murinum modulates its growth and reproductive investment along environmental gradients, balancing phenology, stress tolerance, and limited competitive capacity.

Annual plants complete their life cycle with a single reproductive episode, whereas perennials must balance reproduction with the maintenance of tissues that sustain future growth. Despite the fundamental importance of this distinction, the genomic differences associated with these contrasting life histories remain poorly understood. Here, we utilize independent occurrences of annuality in the grass genus Hordeum to identify recurrent differences between annual and perennial species. Combining transcriptomes from 82 accessions with recently published reference genomes, we compared protein-coding sequence evolution, gene copy number, gene expression and co-expression while accounting for evolutionary non-independence. We found widespread genomic differentiation, with several consistent patterns. Genes involved in cell division and genome maintenance showed evidence of stronger evolutionary constraint in perennials, while gene families associated with developmental regulation and senescence were more frequently retained in higher copy numbers in perennials. Differences in gene expression and coordination were particularly pronounced during reproduction, when perennials showed higher expression of genes involved in cell division, cytoskeletal organisation, cell-wall formation and resource transport, together with extensive reorganisation of gene co-expression relationships. Across these complementary analyses, processes involved in cellular proliferation, developmental regulation and tissue maintenance repeatedly distinguished the two life histories. Our findings suggest that annual-perennial differentiation extends beyond individual flowering regulators to broader genomic differences associated with a more complex coordination of processes balancing growth and senescence in perennials. By identifying these recurrent patterns across evolutionary lineages, this study provides a comparative framework for understanding the genomic differentiation underlying contrasting plant life histories.

Societal Impact Statement: Underutilized species (also known as orphan crops) present opportunities to increase crop diversity and food security. Such crops lack modern genetic tools and knowledge to facilitate efficient modern breeding approaches. A wide collection of tef (Eragrostis tef (Zucc.) Trotter) genotypes was used to identify genomic regions associated with productivity, lodging, and morpho‐physiological traits under contrasting water availabilities. The obtained results are expected to enhance modern breeding and improve tef productivity under traditional and modern cropping systems, thus improving farmers' livelihood and food security.Summary: Tef (E. tef (Zucc.) Trotter) is an allotetraploid (2n = 4x = 40) C4 cereal crop, endemic to Ethiopia and mainly cultivated in the Horn of Africa. Tef is characterized by high grain and feed nutritional qualities and resilience to abiotic and biotic stresses; thus, it holds great potential to sustain food and nutrition security in Africa and other parts of the world. The objective of this study was to identify genomic regions associated with responses to contrasting water regimes, as a basis for future improvement. A tef diversity panel was genotyped with 28,837 single nucleotide polymorphisms (SNPs) and phenotyped for productivity, lodging, and morpho‐physiological traits along two seasons (2020 and 2021) under well‐watered and water‐limited treatments. A genome‐wide association study was performed to identify genomic regions associated with key traits for tef breeding. A total of 107 SNPs were associated with one or more of the studied traits, resulting in 138 marker–trait associations (MTAs) detected under both water treatments. Of these, 22 SNPs were associated with more than one trait, showing either multiple trait (pleiotropic) or multiple environment associations or both. A particularly strong association was found between grain yield, lodging, and time to heading. These findings open new avenues to further research on the genetic basis and physiological mechanisms underlying major traits in tef, as well as to marker‐assisted breeding of drought‐resilient tef cultivars.

SUMMARY: Domestication is considered a model of adaptation that can be used to draw conclusions about the modus operandi of selection in natural systems. Investigating domestication may give insights into how plants react to different intensities of human manipulation, which has direct implication for the continuing efforts of crop improvement. Therefore, scientists of various disciplines study domestication‐related questions to understand the biological and cultural bases of the domestication process. We employed restriction site‐associated DNA sequencing (RAD‐seq) of 494 Pisum sativum (pea) samples from all wild and domesticated groups to analyze the genetic structure of the collection. Patterns of ancient admixture were investigated by analysis of admixture graphs. We used two complementary approaches, one diversity based and one based on differentiation, to detect the selection signatures putatively associated with domestication. An analysis of the subpopulation structure of wild P. sativum revealed five distinct groups with a notable geographic pattern. Pisum abyssinicum clustered unequivocally within the P. sativum complex, without any indication of hybrid origin. We detected 32 genomic regions putatively subjected to selection: 29 in P. sativum ssp. sativum and three in P. abyssinicum. The two domesticated groups did not share regions under selection and did not display similar haplotype patterns within those regions. Wild P. sativum is structured into well‐diverged subgroups. Although Pisum sativum ssp. humile is not supported as a taxonomic entity, the so‐called 'southern humile' is a genuine wild group. Introgression did not shape the variation observed within the sampled germplasm. The two domesticated pea groups display distinct genetic bases of domestication, suggesting two genetically independent domestication events.

Aim: Genetic diversity is a major determinant for the capacity of species to persist and adapt to their environments. Unravelling the factors affecting genetic differentiation is crucial to understand how genetic diversity is shaped and species may react to changing environments. We investigated the drivers of genetic differentiation and their interplay with the evolutionary history in a wild pea to test how those may have affected the distribution of genetic diversity.Location: Mediterranean basin, western Asia.Taxon: Pisum sativum (Fabaceae).Methods: We employed restriction site associated DNA (RAD) sequencing of a collection of 81 wild pea samples. The influence of environmental factors on genetic differentiation was tested by estimating the association of these factors and genetic variation using gradient forest analysis. Stairwayplots were used to estimate past effective population sizes and clines of allele frequencies were analysed to detect past expansion patterns. Association of single nucleotide polymorphisms with environmental variables was tested to find signatures of local adaptation.Results: The effect of the tested factors influencing genetic differentiation was variable among genetic clusters. Climate predictors were most important in all clusters. Land cover was more important in clusters from areas strongly influenced by human land use. We found statistically significant associations of 3623 SNPs with environmental variables. Most of these SNPs were correlated with latitude followed by temperature. Wild peas went through a genetic bottleneck during the last glacial period followed by population recovery. The detected range expansion patterns suggested an eastward range expansion of the European cluster to Turkey and thereof southwards and eastwards.Main conclusion: Drivers of genetic differentiation do not act in a uniform manner within a species. The distribution of genetic variation and the processes affecting this distribution have to be viewed in the context of the hierarchical structure of genetic variation and the environment of its entities to understand how genetic diversity was shaped and may change in the future.