Dynamics and regulation pathways of microbial carbon sequestration in river sediments: A non-equilibrium statistical...

Rivers are recognized as significant carbon sources due to their extensive distribution and dynamic carbon exchange. The transition from riverine carbon emissions to sequestration is critical for assessing the global carbon cycle. Microbial activities dominate carbon transformation in river sediments, driving accumulation and consumption via assimilation and respiration. Microbial carbon fixation is a non-equilibrium process involving continuous matter and energy exchange with the environment. Influenced by multiple environmental factors and stochastic disturbances (e.g., flow velocity, litter input, and nutrient ratios), it poses significant challenges for quantifying carbon fixation and its regulatory pathways. This study is the first to elucidate the complex transition dynamics, regulatory mechanisms, and thresholds of carbon fixation by employing the potential landscape and flux theory from non-equilibrium statistical mechanics. Nitrogen was identified as the most critical environmental factor influencing carbon fixation, following an evaluation of key factors and stochastic perturbations. Two stable system configurations, i.e., carbon loss and carbon fixation, were revealed by the potential energy landscape derived from the Fokker-Planck equation. The system transitions from a carbon-loss state to a carbon-sequestration state along a nitrogen gradient, as shown by the evolutionary trend of the potential energy landscape, with this shift also being potentially triggered by other environmental perturbations. Barrier and transition time analyses demonstrated significant differences in how various disturbances affect carbon transformation, with litter input most substantially enhancing the stability of the carbon sequestration state. Furthermore, critical boundaries for regulating carbon transformation were identified by thresholds of non-equilibrium kinetic and thermodynamic parameters (N = 0.357 g/kg and N = 0.401 g/kg). This framework provides theoretical support for the regulation of carbon fixation in river sediments.