Divergent rhizosphere microbial necromass dynamics between two plant species in response to water addition in a semi-arid region

Microbial necromass carbon influences soil organic carbon (SOC) persistence, yet its response to soil moisture change in semi-arid rhizospheres remains unclear. Avena sativa and Leymus chinensis, which are widely cultivated in semi-arid areas, were selected for a three-month indoor pot cultivation experiment. The responses of soil microbial necromass carbon to water addition and the key drivers in the rhizosphere soil of these plants were identified. The results demonstrated that water addition significantly decreased the concentrations of bacterial necromass carbon (BNC), fungal necromass carbon (FNC), and SOC in the Avena sativa rhizosphere, but increased them in the Leymus chinensis rhizosphere. However, water addition consistently reduced the contribution of microbial necromass carbon to SOC across both rhizosphere soils. The FNC accounted for a larger proportion of SOC than BNC, but the dynamic of SOC was more closely associated with the change in BNC. Both BNC and FNC showed significant correlations with microbial properties (gene abundances and enzyme activities). However, the BNC was closely related to soil nutrient availability, whereas FNC was linked to the ratio of SOC to total nitrogen. These findings demonstrate that rhizosphere microbial necromass carbon dynamics in response to moisture change are plant-specific and driven by distinct factors. Therefore, accurately projecting future SOC stability in semi-arid regions requires models to incorporate plant-specific traits and microbial mediation.