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Root exudates are an important pathway for plant–microbial interactions and are highly sensitive to climate change. However, how extreme drought affects root exudates and the main components, as well as species‐specific differences in response magnitude and direction, are poorly understood. In this study, root exudation rates of total carbon (C) and its components (e.g., sugar, organic acid, and amino acid) were measured under the control and extreme drought treatments (i.e., 70% throughfall reduction) by in situ collection of four tree species with different growth rates in a subtropical forest. We also quantified soil properties, root morphological traits, and mycorrhizal infection rates to examine the driving factors underlying variations in root exudation. Our results showed that extreme drought significantly decreased root exudation rates of total C, sugar, and amino acid by 17.8%, 30.8%, and 35.0%, respectively, but increased root exudation rate of organic acid by 38.6%, which were largely associated with drought‐induced changes in tree growth rates, root morphological traits, and mycorrhizal infection rates. Specifically, trees with relatively high growth rates were more responsive to drought for root exudation rates compared with those with relatively low growth rates, which were closely related to root morphological traits and mycorrhizal infection rates. These findings highlight the importance of plant growth strategy in mediating drought‐induced changes in root exudation rates. The coordinations among root exudation rates, root morphological traits, and mycorrhizal symbioses in response to drought could be incorporated into land surface models to improve the prediction of climate change impacts on rhizosphere C dynamics in forest ecosystems. [ABSTRACT FROM AUTHOR]

Microbial necromass is considered as one of the primary drivers in soil organic carbon (SOC) formation and persistence. However, how microbial traits (e.g., diversity, composition) influence microbial necromass C and its contribution to SOC remains unclear, especially under persistent drought. Here, we took advantage of a 7-year Throughfall Exclusion Experiment (TEE) to examine effects of drought on microbial necromass C and its contribution to SOC at different soil depths in a subtropical forest. Microbial DNA sequencing and amino sugars biomarker analysis were integrated to probe regulation of microbial traits on microbial necromass C and its contribution to SOC storage under drought. Our results showed that persistent drought increased the contribution of microbial necromass C to SOC with increasing soil depth, ranging from 32.0% in 0–10 cm to 39.7% in 45–60 cm for fungal necromass and from 15.3% in 0–10 cm to 22.6% in 45–60 cm for bacterial one under drought. Interestingly, bacterial necromass C was more important for SOC accumulation than fungal necromass C in subsoil while vice versa in topsoil. Moreover, drought significantly altered the rare microbial diversity and community composition. Drought-induced shifts in rare microbial taxa largely explained the contributions of fungal and bacterial necromass C to SOC in both sub- and top-soils. Thus, microbial traits, especially rare microbial diversity and community composition, regulated the contribution of microbial necromass C to SOC at different soil depths. These findings highlight the crucial role of the rare microbial community on bacterial- and fungal-derived C in subsoil and topsoil, especially under persistent drought, which should be incorporated into land surface models to improve SOC prediction under future climate change. • Drought increased contribution of microbial necromass C to SOC. • Bacterial necromass C contributed more to SOC than fungi in subsoil. • In topsoil, fungal necromass C was more important for SOC storage than bacteria. • Rare microbial composition regulate contribution of microbial necromass C to SOC. [ABSTRACT FROM AUTHOR]