Precipitation is a primary determinant of plant community structure in drylands. However, the empirical evidence and predictions are lacking for how plant functional diversity in desert and steppe communities respond to altered precipitation regimes.

We examined how precipitation changes along the natural and experimental gradients affect different components of functional diversity in desert-shrub and steppe-grass communities. We compared the associations of precipitation changes with community-weighted means (CWM) of six traits, functional divergence (FDvar) of each single-trait, and multi-trait functional richness (FRic) and dispersion (FDis) for shrub and grass communities along the natural and experimental gradients. We also disentangle the roles of species turnover and intraspecific variations in affecting the responses of different functional diversity to precipitation changes.

We found that in general, the similar responses of functional traits or diversity to both the natural and experimental precipitation gradient were dependent on plant community type. Across both two gradients, precipitation was positively associated with CWM of plant height and negatively associated with the CWM of specific leaf area and leaf thickness in grass community, while positively associated with FDvar of four traits and FDis in shrub communities. Both species turnover and intraspecific variations contributed to the responses of grass community traits to precipitation changes across both two gradients, and to functional divergence of traits and FDis in shrub community along the natural gradient. In contrast, species turnover variations contributed to functional divergence of traits and FDis in shrub community in experiment.

These results suggest that there is better concordance between the effects of naturally and experimentally increased precipitation on functional diversity of plant communities, but different mechanisms behind the relationship of functional diversity-precipitation between shrub and grass communities. Grass communities can adapt to precipitation changes by average trait differences, while shrub communities persist through the functional divergence of single-trait and multi-trait dispersion, thus highlighting the important differences in adaptive strategies between shrub and grass communities. Our findings demonstrate that the short-term responses of plant communities to manipulative precipitation changes can reflect long-term shifts at spatial scales depending on the specific functional trait and diversity.

The dataset was collected form a comparative study of how precipitation changes along the natural and experimental gradients affect different components of functional diversity in desert-shrub and steppe-grass communities. The trait data on CWM were calculated by multiplying the trait value of each species by its relative biomass in the community. FDvar were calculated form the variation in single-trait value weighted by the abundance of each species in plant community. Functional richness (FRic) and dispersion (FDis) were calculated form log-transformed values of six single traits. Functional diversity indices of CWM, FDvar, FRic and FDis were calculated by the FDiversity and R package.