Hydrodynamic Disturbance-Driven Suppression of Microbial Necromass Carbon Accumulation in Lateral Carbon Migration

Microbial necromass carbon (MNC), a critical component of the soil organic carbon (SOC) pool, constitutes a key component on global carbon cycling via the dynamic equilibrium between its formation and decomposition. In aquatic-terrestrial interfaces (e.g., river systems), hydrodynamic disturbances may critically regulate the fate of MNC during terrestrial-to-aquatic carbon transport. However, dynamic responses of MNC to hydrodynamic disturbances during lateral transport remain systematically underexplored. This study employed controlled experiments simulating lateral transport processes to unravel hydrodynamic disturbance-driven MNC depletion mechanisms. Results demonstrated that hydrodynamic disturbances significantly reduced the contribution of MNC to SOC (disturbance treatment: 46.65% vs. control: 55.17%; P < 0.001). In contrast, inundation alone (static water treatment: 59.32% vs. control: 55.17%; P > 0.05) exerted negligible influence. Path analysis revealed the core mechanisms of hydrodynamic suppression on MNC accumulation: (1) triggering positive “desorption-mineralization” feedback by destabilizing MNC occurrence forms and enhancing hydrolytic enzyme activity (path coefficient = 0.60, P < 0.05); (2) generating negative “re-synthesis” feedback through reduced microbial biomass inputs (path coefficient = -0.48, P < 0.05). Synergistic interactions between these coupled pathways ultimately suppressed MNC accumulation (standardized total effect = -0.39). These findings advance theoretical understanding of carbon cycling during lateral transport and provide critical insights for optimizing soil carbon conservation and ecological management strategies in erosion-prone regions.