A synthesis of ecosystem aboveground productivity and its process variables under simulated drought stress

Abstract

Abstract Projected increases in drought duration and intensity under climate change considerably affect aboveground productivity (ANPP) and associated process variables (photosynthesis rates (Pn), stomatal conductance (gs), soil respiration (Rs) and soil water content (SWC)). Although ANPP has been extensively studied across the ecosystems, there is a little consensus on how the spatiotemporal patterns of ANPP will be altered with increasing drought stress. Here, we present a global meta‐analysis of ANPP and the four variables (610 observations from 78 studies) for drought duration, intensity and their combination. Forest‐ANPP had stronger negative responses to long‐term drought (34.44%; ≥4 years) than short‐term drought (10.78%; ≤1 year) and decreased more in Mediterranean forests than in tropical forests. Decreases in Pn and gs were strongest under long‐term moderate drought. In the short term, Rs increased by 5.66% under light drought, but decreased by 14.12% and 28.43% under moderate and severe droughts. Grass‐ANPP showed a nonlinear decrease with extended duration and the rate slowed. Within light to severe intensities, ANPP decreased linearly, but became stable under extreme condition. In the short term, ANPP reduced more seriously with increasing drought intensity (12.01%‐30.34%). With aggravation of drought stress, the reductions in Rs and SWC increased. There was significant heterogeneity in grassland responses to drought stress. The greatest decreases in ANPP, Pn and gs were observed in North America, and the reductions in Rs and SWC were greater in Western Europe. Shrub‐ANPP showed stronger negative responses to long‐term moderate drought (12.59%). Pn and gs declined significantly with increasing drought intensity. Variations in Rs to drought duration, intensity and their combination were more complex, either showing positive or negative responses (dominated). Synthesis. Forest‐ANPP shows high sensitivity to long‐term moderate drought, whereas grass‐ANPP is more responsive to short‐term drought. Compared to forests and grasslands, shrub‐ANPP exhibits less sensitivity to droughts. Different responses of ecosystems were predominantly driven by physiological mechanisms or species differences in turnover time, community architecture and drought adaptation strategies. Given these findings, future studies should focus on nonlinear patterns, response thresholds and adaptation mechanisms when predicting and modeling feedback between ecosystems and climate change.