Functional approach to xerothermic grasslands in Central Germany: trait composition, dominant grasses and soil factors

Functional traits mediate how species and communities respond to (or affect) environmental gradients. These are impacted by global change, which has led to e.g. climate change and land-use change, affecting soil conditions, species richness and functional diversity in, among others, xerothermic (respectively dry or semidry) grasslands. Within the last decades, the dominance of grass species like Bromus erectus has increased in such grasslands in Central Germany, but factors driving their intraspecific trait variability (ITV) are not yet well understood. The aim of our study was, on the one hand, to compare the functional trait composition of two grassland types, namely dry and semidry, using multi- and single-trait approaches and to assess the effects of soil properties on these traits and, on the other hand, to reveal differences in functional traits and their ITV between the five dominant grasses B. erectus, Brachypodium pinnatum, Festuca rupicola, Helictotrichon pratense and Stipa capillata. Based on vegetation relevés, functional traits (VPH – vegetative plant height, LDM – leaf dry mass, LA – leaf area, SLA – specific leaf area, LDMC – leaf dry matter content, LNC – leaf nitrogen concentration, LCC – leaf carbon concentration, leaf C/N ratio) were measured and soil factors (soil depth, pH value, CaCO₃ content, soil N and C content, soil C/N ratio) analysed. For each plot, the community weighted mean (CWM) of all functional traits was calculated to determine differences between the two grassland types and the coefficient of variation was used for interpreting differences in the ITV between the five grasses. There were minor differences between dry and semidry grasslands in the CWM of the functional traits LDM, LA, LNC and LCC, while other traits did not differ between the two grassland types. Soil factors had little effects on the trait composition of dry and semidry grasslands, although soil depth, CaCO3 content and C/N ratio had the greatest influence on CWM and were potentially the strongest drivers for differentiation. The five grasses had species-specific trait distributions but showed relatively similar ITV, so we conclude that B. erectus was not more adapted to changing environmental conditions than the other grasses. Generally, we only found minor changes in the functional trait composition of dry and semidry grasslands in Central Germany and thus the environmental gradient was too small to derive clear differences in the ecosystem function between both grassland types, although the functional structure was largely determined by the dominant grasses.