Microbial Complexity and Diversity Enhance Microbial Necromass Nitrogen Sequestration Along a Latitudinal Gradient

Human activities have led to nitrogen enrichments in aquatic environments, facilitating microbial nitrogen turnover and microbial necromass nitrogen (MNN) formation. The extent to which abiotic and biotic factors mediate MNN sequestration in estuarine and coastal wetlands, however, remains poorly understood. Here, we examined MNN concentrations, sediment properties, and microbial traits along a latitudinal gradient. MNN concentrations shifted by 2 orders of magnitude, ranging between 0.02 and 1.25 mg g^–1 and equivalent to 26–86% of total nitrogen. Fungal necromass dominated MNN over bacteria, suggesting the preferential preservation of fungal necromass. Total nitrogen rather than temperature showed a greater influence on MNN, suggesting the predominance of nitrogen in shaping MNN variation. Climate temperature and sediment variables explained 12.8% and 47.8% of the MNN variation, respectively. MNN significantly correlated with microbial diversity and abundance, highlighting the crucial role of microbially mediated necromass N formation. High network complexity and stability also contributed to higher MNN concentrations, which could be due to the higher resource acquisition ability and greater resilience to environmental pressures. These findings suggest that MNN constitutes a crucial component of nitrogen pools, and the sequestration can be enhanced by microbial complexity and diversity, which is of great significance to alleviate nitrogen pollution and ecological restoration in global estuarine and coastal wetlands.