Global positive and adaptive effects of experimental warming on soil microbe traits

Global warming is a major environmental concern with the potential to influence soil microorganisms that play important roles in carbon (C) cycling in terrestrial ecosystems. However, limited understanding of soil microbial responses to warming hinders predictions of ecosystem feedback to climate change. Thus, we conducted a global meta-analysis of 1594 pairwise observations from 215 peer-reviewed articles to examine the responses of soil microbial traits to warming. On average, warming increased soil respiration, microbial respiration, Gram-negative bacteria, Gram-positive bacteria, muramic acid, and bacterial necromass C by 16.9 %, 13.1 %, 22.7 %, 12.1 %, 15.2 %, and 17.9 %, respectively, while decreased soil water content by 10.5 %. Notably, these positive effects peaked at shorter durations and lower warming magnitudes, then diminished as both increased. Regression analysis showed that the response ratios for several microbial traits (microbial respiration, total phospholipid fatty acids, bacteria and fungal contents, Gram-negative and Gram-positive bacteria) decreased significantly and negatively with the mean annual precipitation (all P < 0.05). Finally, structural equation modeling showed that 26-65 % of the variations in soil respiration, total phospholipid fatty acids, amino sugar, microbial necromass C, and microbial biomass C and N could be explained by differences in ecosystem types, climate conditions, and experimental setups. Our findings highlight the importance of the duration and magnitude of warming for regulating the responses of soil microbial traits, and the dependence of the effects of warming upon ecosystem types and climate conditions. These findings provide critical insights for refining Earth system models and guiding ecosystem management strategies aimed at enhancing soil carbon sequestration under climate warming.