| 摘 要： |
Global hydroclimatic variability is increasing with more frequent extreme dry and wet years, severely destabilizing terrestrial ecosystem productivity. However, what regulates the consequence of precipitation extremes on productivity remains unclear. Based on a 9-year field manipulation experiment on the Qinghai-Tibetan Plateau, we found that the responses of gross primary productivity (GPP) to extreme drought and wetness were differentially regulated by nitrogen (N) deposition. Over increasing N deposition, extreme dry events reduced GPP more. Among the 12 biotic and abiotic factors examined, this was mostly explained by the increased plant canopy height and proportion of drought-sensitive species under N deposition, making photosynthesis more sensitive to hydraulic stress. While extreme wet events increased GPP, their effect did not shift over N deposition. These site observations were complemented by a global synthesis derived from the GOSIF GPP dataset, which showed that GPP sensitivity to extreme drought was larger in ecosystems with higher N deposition, but GPP sensitivity to extreme wetness did not change with N deposition. Our findings indicate that intensified hydroclimatic variability would lead to a greater loss of land carbon sinks in the context of increasing N deposition, due to that GPP losses during extreme dry years are more pronounced, yet without a synchronous increase in GPP gains during extreme wet years. The study implies that the conservation and management against climate extremes merit particular attention in ecosystems subject to N deposition. Global hydroclimatic variability is intensifying, with more frequent extreme dry and wet years severely destabilizing terrestrial ecosystem productivity, but what regulates this consequence remains unclear. Combining a field experiment with a global synthesis, we found that over increasing N deposition, extreme dry events reduced productivity more. While extreme wet events increased productivity, their effect did not shift over N deposition. Consequently, the enhanced hydroclimatic variability will increasingly reduce productivity as N deposition increases once extreme drought reduces productivity more than extreme wetness induced an increase in productivity. These findings have important implications for ecosystem conservation and management against climate extremes.image |
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