Forest diversification-induced soil organic carbon accumulation associated with micro-food web complexification

Forest plantations often have lower levels of soil organic carbon (SOC), which plays a critical role in terrestrial carbon cycling and climate change mitigation. While belowground organisms are recognized as key drivers of SOC dynamics, the nature in which multitrophic interactions within the soil micro-food web influence carbon accumulation remain poorly understood. Here, we combined a meta-analysis with long-term field experiment comparing monoculture plantations with more diversified subtropical forests to examine the diversity and interactions of among soil organisms and their metabolic capacity (via enzyme activities and stoichiometry), and how those link to SOC accumulation. We found that more diversified plantations have higher SOC accumulation, likely as a result of more diverse and complex micro-food web interactions. Mechanistically, this enhanced network complexity, particularly through strengthened positive associations, lead to elevated enzyme activity and a reduced enzymatic stoichiometric imbalance. Our findings demonstrate that tree species diversity influences SOC sequestration by fostering complex multitrophic interactions within the soil micro-food webs. This complexity underpins belowground metabolic homeostasis, and highlights the importance of managing forest diversity to enhance soil carbon storage, maintain soil fertility, and mitigate climate change.