Differential Responses of Community Nonstructural Carbohydrate to Drought Manipulation Along a Natural Aridity Gradient

Plant nonstructural carbohydrates (NSC) can reflect community and ecosystem responses to environmental changes such as water availability. Climate change is predicted to increase aridity and the frequency of extreme drought events in grasslands, but it is unclear how community-scale NSC will respond to drought or how such responses may vary along aridity gradients. We experimentally imposed a 4-year drought in six grasslands along a natural aridity gradient and measured the community-weighted mean of leaf soluble sugar (SSCWM) and total leaf NSC (NSCCWM) concentrations. We observed a bell-shape relationship across this gradient, where SSCWM and total NSCCWM concentrations were lowest at intermediate aridity, with this pattern driven primarily by species turnover. Drought manipulation increased both SSCWM and total NSCCWM concentrations at intermediately arid grassland but decreased total NSCCWM concentrations at one site. These differential responses to experimental drought depended on the relative role of species turnover and intraspecific variation in driving SSCWM and total NSCCWM. Specifically, the synergistic effects of species turnover and intraspecific variation driven the responses of leaf NSC concentrations to drought, while their antagonistic effects diminished the effect of drought on plant SSCWM and total NSCCWM concentrations. Plant resource strategies were more acquisitive, via increasing chlorophyllCWM content, to offset reduced NSCCWM concentrations with increasing aridity at drier sites, but more conservative (i.e., decreased plant heightCWM) to reduce NSC consumption at more mesic sites. The relationship between water availability and NSCCWM concentrations may contribute to community drought resistance and improve plant viability and adaptation strategies to a changing climate.