Meta-analysis shows non-uniform responses of above- and belowground productivity to drought

Terrestrial productivity underpins ecosystem carbon (C) cycling and multi-trophic diversity. Despite the negative impacts of drought on terrestrial C cycling, our understanding of the responses of above- and belowground productivity to drought remains incomplete. Here, we synthesized the responses of terrestrial productivity and soil factors (e.g., soil moisture, soil pH, soil C, soil nitrogen (N), soil C:N, fungi:bacteria ratio, and microbial biomass C) to drought via a global meta-analysis of 734 observations from 107 studies. Our results revealed that the productivity variables above- and belowground (i.e., net primary productivity, aboveground net primary productivity, belowground net primary productivity, total biomass, aboveground biomass, root biomass, gross ecosystem productivity, and net ecosystem productivity) were decreased across all ecosystems. However, drought did not significantly affect litter mass across all ecosystems, and the responses of above- and belowground productivity to drought were non-uniform. Furthermore, the responses of these productivity variables to drought were more pronounced with drought intensity and duration, and consistent across ecosystem types and background climates. Drought significantly decreased soil moisture, soil C concentrations, soil C:N ratios, and microbial biomass C, whereas it enhanced soil pH values and fungi:bacteria ratios. Moreover, the negative effects of drought on above- and belowground productivity variables were correlated mostly with the response of soil pH to drought among all soil factors. Our study indicated that litter biomass, which mostly represents productivity levels via traditional ecosystem models, was not able to predict the responses of terrestrial ecosystem productivity to drought. The strong relationship between the responses of soil pH and terrestrial productivity to drought suggests that the incorporation of soil pH into Earth system models might facilitate the prediction of terrestrial C cycling and its feedbacks to drought.