Divergent responses of grassland productivity and plant diversity to intra-annual precipitation variability across climate regions: A global synthesis

Global warming intensifies the hydrological cycle and may result in
changes in the frequency and intensity of precipitation events. Although
the effects of changes in precipitation amount and inter-annual
precipitation variability on terrestrial plant productivity and carbon
sequestration have been well studied, how intra-annual precipitation
variability affects terrestrial ecosystem function remains unclear. Here,
we synthesized field manipulative experiments from 71 publications to
quantify the effects of intra-annual precipitation variability increases
(IPVI) on community biomass and plant diversity in grasslands worldwide.
 At the global scale, we found that IPVI generally increased
grassland community aboveground biomass (AGB) by 6%, and decreased grass
biomass and soil ammonium nitrogen by 12% and 31%, respectively. IPVI
stimulated AGB, belowground biomass, and plant species richness in arid
regions, but not changed them in humid regions. Changes in AGB under IPVI
were related to changes in the biomass of plant functional groups, species
richness, and soil moisture. Structural equation modelling demonstrated
that that climate conditions (mean annual temperature and mean annual
precipitation) and background soil properties (soil sand content and soil
organic carbon content) jointly regulated grassland AGB responses to IPVI
across climate types. Synthesis: Overall, our study shows that grassland
productivity and diversity may increase under IPVI in arid climates, and
that humid grasslands may be highly resistant to the effects of IPVI.
These findings have important implications for understanding ecosystem
carbon cycling under global precipitation change scenarios.