Objective To reveal the differences in the response of soil carbon and nitrogen content to tree species diversity in forest ecosystems in different climatic zones, and to explore the key biotic and abiotic factors affecting this response.

Method We collected the data of altitude, air temperature, soil properties (including soil carbon (C), nitrogen (N), C/N ratio), as well as fungal diversity from sample plots with both tree species mixtures and monocultures. In total, 214 sets of data were used to conduct meta analysis, with a random-effect model calculating effect size. Additionally, the explanatory weights of biotic and abiotic variables influencing the effect of tree richness were analyzed.

Result We found that the responses of soil C and N contents to tree richness varied across forest ecosystems, with the strength of tree richness effects on soil C and N contents gradually diminishing from tropical to mid-temperate forest ecosystems. Moreover, the effects of tree richness on soil C and N contents in tropical and subtropical forest ecosystems were primarily driven by altitude and soil pH, rather than soil fungal diversity. In contrast, cascading effects of tree richness on soil C and N contents were observed via modulating soil fungal diversity in warm-temperate and mid-temperate forest ecosystems.

Conclusion The response patterns of soil carbon and nitrogen contents in forest ecosystems of different climate zones in China to tree species diversity, to some extent, explain the variability mechanisms of forest tree species diversity on soil carbon pools in local scale studies, and also indicate that changes in tree species diversity may have a more severe impact on soil carbon pools in tropical and subtropical forests.