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Moisture availability is the main limiting factor of plant growth and biomass production in arid and semi-arid grasslands. The question whether plant responses to changing precipitation are species-specific, or change over entire plant communities is still controversial. Our study focussed on intraspecific changes in the plant traits canopy height, plant width, specific leaf area, chlorophyll fluorescence, performance index, and individual biomass of three congeneric species pairs with changing precipitation in Mongolian rangelands, covering a gradient from the desert to the forest steppes. Using this trait data set, we focussed on three questions: (i) Is the replacement of congeneric species along an environmental gradient also reflected in their trait values? (ii) Can intraspecific trait variation patterns be derived from patterns in species abundances, i.e., are trait values optimal where species are most abundant? (iii) Is the within-population trait variability lowest in populations growing under very dry conditions, i.e., under highest environmental stress, caused by stronger filtering? We tested the responses of the six traits to changing precipitation according to species’ identity and abundance. We found unimodal relationships between most of the species’ traits and precipitation, and strong associations between species abundances and trait values, but not for all investigated species. Trait variability did not significantly differ between populations from different positions along the precipitation gradient. Our results highlight that species show multiple or even opposite trait responses along the precipitation gradient. It thus remains challenging to predict how plant distributions will shift under changing environmental conditions based on their trait composition.

In dry steppes, strong climatic constraints, especially highly variable precipitation, and grazing are the most important factors controlling plant life. Growth is strongly limited by water availability, while grazing may affect species presence and performance. However, there is a lack of studies on population genetics of dryland plants in general, and of those addressing grazing effects in particular. To determine the landscape-scale genetic structure of dryland species, and if grazing has an impact on that, we chose the Eurasian steppe grass Stipa glareosa for a population genetic study employing nine polymorphic Simple Sequence Repeat (SSR) markers. We assessed genetic fingerprints of 200 individuals from six populations in Mongolia, which were sampled along a large-scale precipitation and altitudinal gradient. Nested within this gradient, sub-populations were sampled along short local transects representing different grazing intensities. Overall, S. glareosa populations showed rather low levels of genetic diversity at a mean Bruvo distance among individuals within a given population of 0.494 (mean expected heterozygosity He = 0.053). Linear mixed model analysis implied that genetic diversity was affected by both climatic constraints and local grazing conditions. We found a moderate isolation-by-distance pattern across all populations; grazing additionally influenced the genetic structure at local scale. Analysis of Molecular Variance revealed a modest genetic differentiation between populations (9 % of variation) and among sub-populations representing different grazing levels (11 %). Moreover, we detected indicator alleles that were exclusive for populations along the precipitation gradient; other alleles were associated with certain grazing levels across all populations. Thus, our data suggest that climatic constraints affect the genetic structure of S. glareosa populations, while at local scales differences in grazing disturbance may also matter.