Drought effects on microbial carbon use efficiency regulated by particulate organic carbon and microbial life history strategy in a subtropical forest

This increase in subsoil CUE was attributed to the greater stress tolerance of subsoil microbial communities, as indicated by a significant increase in the bacterial yield-to-acquisition (Y/A) ratio under drought. Mechanistically, drought-induced changes in microbial CUE across soil depths were jointly regulated by shifts in substrate availability, particularly particulate organic carbon (POC), and changes in microbial life-history strategies, reflecting the trade-off between growth yield and resource acquisition.

Across both soil depths, the relative abundance of Proteobacteria emerged as the strongest microbial predictor of CUE, while both bacterial and fungal richness were positively correlated with CUE. These findings highlight the importance of incorporating depth-dependent POC dynamics and microbial Y/A strategy shifts into land surface models to improve predictions of soil carbon-climate feedbacks.