Functional diversity response to geographic and experimental precipitation gradients varies with plant community type

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.