Co-existence strategies and carbon sequestration contributions of bacterial generalists and specialists in natural wetlands under land use and land cover change.

The function of natural wetlands (NW) as carbon sinks or sources is largely determined by the bacterial community structure, diversity, and function metabolism. However, the responses of generalists and specialists to changes in soil organic carbon (SOC) from NWs undergoing land use and/or land cover change (LULCC) remain unclear. In this study, using 1124 amplicon samples and associated environmental parameters for NWs and corresponding LULCC types globally, the distribution patterns of generalists and specialists, species coexistence, assembly processes, and responses to SOC were evaluated. The findings indicated that generalists rather than specialists exhibited higher Bray-Curtis dissimilarity indices and turnover rates following LULCC. Generalists and specialists had smaller niche overlap indices and more complex co-occurrence network topological parameters after LULCC. This means that species interactions transitioned from competition to cooperation following LULCC, primarily driven by an increasing influence of deterministic processes. Notably, when NWs were converted into LULCCs, the metabolic abundance and functional redundancy of generalists gradually decreased, while specialists showed the opposite trend. This shift in functional metabolism is the main driver of the decline in carbon content. Because generalists' metabolic abundance showed a transition from a positive (slope = 4.136, p = 0.026) to a negative (slope = -1.598, p = 0.008) correlation with SOC from NW to LULCC, while specialists exhibited a progressively stronger negative response (slope = -1.980, p = 0.026). Specifically, the response relationship between total community metabolic abundance and SOC content shifted from positive to negative, with a stronger negative response. This undoubtedly has a negative impact on the carbon sequestration in native ecosystems after LULCC. Changes in local environmental factors were identified as the primary cause of this phenomenon. Overall, these findings provide a theoretical basis for refining carbon cycle models that incorporate bacterial generalists and specialists.