Effects of warming and precipitation changes on soil GHG fluxes: A meta- analysis

Increased atmospheric greenhouse gas (GHG) concentrations resulting from human activities lead to climate change, including global warming and changes of precipitation patterns worldwide, which in turn would have profound effects on soil GHG emissions. Nonetheless, the impact of the combination of warming and precipitation changes on all three major biogenic GHGs (CO2, CH4 and N2O) has not been synthesized, to build a global synthesis. In this study, we conducted a global meta-analysis concerning the effects of warming and precipitation changes and their interactions on soil GHG fluxes and explored the potential factors by synthesizing 39 published studies worldwide. Across all studies, combination of warming and increased precipitation showed more significant effect on CO2 emissions (24.0%) than the individual effect of warming (8.6%) and increased precipitation (20.8%). Additionally, warming increased N2O emissions (28. 3%), and decreased precipitation reduced CO2 (-8.5%) and N2O (-7.1%) emissions, while the combination of warming and decreased precipitation also showed negative effects on CO2 (-7.6%) and N2O (-14.6 %) emissions. The interactive effects of warming and precipitation changes on CO2 emissions were usually additive, whereas CO2 and N2O emissions were dominated by synergistic effects under warming and decreased precipitation. Moreover, climate, biome, duration, and season of manipulations also affected soil GHG fluxes as well. Furthermore, we also found the threshold effects of changes in soil temperature and moisture on CO2 and N2O emissions under warming and precipitation changes. The findings indicate that both warming and precipitation changes substantially affect GHG emissions and highlight the urgent need to study the effect of the combination of warming and precipitation changes on C and N cycling under ongoing climate change.