Abstract
Aims Soil microbes are key to myriad processes in terrestrial ecosystems. Elevated CO 2 represents a dominant driver of global climate change; however, it remains unclear to what extent elevated CO 2 impacts soil microbial communities at ecosystem and global scales. Here, we sought to address the following questions: (a) Do the compositions of microbial communities shift from K ‐ to r ‐strategists under elevated CO 2 ? (b) What is the extent of the compositional shifts of microbial communities affected by elevated CO 2 concentrations, experimental duration, ecosystem types and/or background climates? (c) Are the responses of microbial communities to elevated CO 2 associated with changes in soil pH and carbon and nitrogen availabilities? Location Global. Time period 1998–2020. Major taxa studied Soil microbes. Methods We performed a global meta‐analysis of 965 observations from 122 studies, which tested the effects of elevated CO 2 on microbial communities. The data covered broad variations in ecosystems, climate, CO 2 concentrations, experimental duration, and soil factors. Results We revealed that elevated CO 2 decreased the K ‐ to r ‐strategist ratios with decreasing fungi : bacteria, Gram+ : Gram– bacteria, and Acidobacteria : Proteobacteria ratios, and increased bacterial biomass, microbial biomass carbon, Gram– bacteria, and Acidobacteria abundance. Moreover, the shifts from K ‐ to r ‐strategists were more pronounced under higher CO 2 concentrations and longer experimental durations. The responses of microbial attributes to elevated CO 2 did not differ significantly among croplands, forests and grasslands. Furthermore, the response of microbial biomass to elevated CO 2 was negatively correlated with the response of soil pH, while those of bacterial biomass and fungi : bacteria ratios were positively correlated with those of soil organic carbon and soil carbon : nitrogen ratios, respectively. Main conclusions Our results suggest that elevated CO 2 shifts soil microbial communities from K ‐ to r ‐strategists, and provide supportive evidence for understanding responses of soil microbial processes to elevated CO 2 .