Precipitation trends cause large uncertainties in grassland carbon budgets—a global meta-analysis

Abstract

Continuous global warming exacerbates the worldwide hydrological cycle, and alterations in precipitation patterns affect the carbon cycle in grassland ecosystems. The consistency of grassland ecosystem responses to precipitation fluctuations remains unclear, despite extensive research on carbon cycling responses in various ecosystems. Here, we collected data from 109 studies (3129 observations in total) to assess the response of carbon cycle variables to precipitation changes in three grassland types (desert grassland, arid grassland, and wet grassland) at a global scale. The results show that the carbon cycle of grasslands had a wide asymmetric response to changes in precipitation. Increased precipitation promoted carbon input and carbon output in the three grassland types, whereas decreased precipitation inhibited both processes. The response of soil respiration (Rs) to increased precipitation was the lowest in the wet grassland (16.51 %) and the highest in the desert grassland (28.72 %), whereas the response to decreased precipitation was the highest in the arid grassland (-34 %) and the lowest in the wet grassland (-15.37 %). Interestingly, autotrophic respiration (Ra) responded more to increased precipitation than to decreased precipitation, with wet grasslands exhibiting a 10 times greater response. Moreover, the net ecosystem exchange (NEE) of arid grasslands responded more strongly to decreased precipitation, whereas the NEE of desert grasslands responded more strongly to increased precipitation. The natural climate of grasslands affected their response to precipitation management. As the treatment time increased, the response of soil respiration in the desert grasslands gradually decreased, whereas the response in the wet grasslands gradually increased. There was no significant temporal trend in arid grasslands. The natural climate of grassland ecosystems affected their response to precipitation treatments, particularly grassland moisture conditions, which may be the main limiting factor regulating the response of grassland ecosystems to the carbon cycle.