Rhizosphere drives microbial necromass carbon accumulation via enhanced carbon use efficiency: Evidence from a common garden experiment

Soil carbon (C) sequestration is a core issue in global C cycle research, and the rhizosphere, as a hotspot of plant-soil-microbe interactions, still requires in-depth analysis of its mechanism in the formation and stabilization of soil C. This study, based on the "microbial C pump" theory, focuses on the differences in microbial C transformation between the rhizosphere and bulk soils, aiming to reveal how microbial metabolic efficiency regulate the differences in soil C sequestration derived from microbial necromss C between these two soil compartments. We performs a common garden experiment, by measuring amino sugars, systematically compared the differences in the contribution of microbial necromass C to soil organic carbon (SOC) in the rhizosphere of ten tree species and bulk soils. Simultaneously, the 18 O-H 2 O labeling technique was used to determine microbial carbon use efficiency (CUE), and the intrinsic relationship between CUE and microbial necromass C accumulation was analyzed. The results showed: (1) The microbial necromass C content in the rhizosphere was significantly higher than that in the bulk soil, increasing by an average of 35.3%; (2) The contribution of microbial necromass C to SOC in the rhizosphere was 69.1% higher than that in the bulk soil; (3) The average microbial CUE in the rhizosphere was 192.6% higher than that in the bulk soil, and was significantly positively correlated with the content of necromass C in the rhizosphere and/or bulk soil. These results consistently indicate that the rhizosphere promotes the accumulation of microbial-derived C through enhancing microbial CUE. Our study mechanistically confirmed the key role of the rhizosphere for soil C sequestration, not only deepening the understanding of the interaction between plants and microorganisms driving the soil C cycle, but also providing scientific evidence for regulating rhizosphere processes to enhance the C sequestration capacity of ecosystems.