Persistent Drought-Induced Trade-Off of Fungal and Bacterial Residues on Soil Carbon Dynamics in Subtropical Evergreen Forests

Global climate change has greatly accelerated hydrological processes, causing significant increases in frequency and intensity of drought events, which may have a great impact on soil carbon (C) dynamics. Recent studies have emphasized that microbial residues are crucial regulators in controlling soil C turnover and stability. However, how persistent drought influences soil microbial residues to regulate soil C cycling remains unclear, especially in forest ecosystems. In this study, we investigated microbial residues and soil C dynamics during a 7-year drought by a Throughfall Exclusion Experiment (TEE) in a subtropical evergreen forest of Eastern China. Our results showed that fungal residues significantly decreased with increasing drought duration, which were mainly induced by the decline of soil N and soil moisture, probably causing a decrease in soil C under the 7-year persistent drought. In contrast, bacterial residues increased with drought duration due to fast adaption of bacteria to drought and aggregate protection. The retention of bacterial residues might be preserved as a “nutrient reservoir” to cope with the long-term drought in the near future. These results suggest persistent drought-induced trade-off between fungal and bacterial residues in contributing to soil C dynamics. Fungal residues were the essential prerequisite for soil C sequestration in response to drought, while bacterial residues may mainly regulate soil C cycling under the prolonged drought. Therefore, microbial residues should be explored to understand the responses of microbial-derived C to drought, which could be integrated into terrestrial C models to accurately predict soil C dynamics in response to unpredictable climate regimes in forest ecosystems.