Seasonal Shifts in Metal-Associated Fungal Community Dynamics and Functional Potentials in Chinese Coastal Sediments

Coastal sediments are critical hotspots in global biogeochemical cycles, acting as reservoirs and transformation zones for terrestrial-marine metal fluxes. Yet, the large-scale ecological significance of sediment fungi, particularly their interactions with metals, remains poorly understood. Here, leveraging a continental-scale seasonal survey across China's marginal seas, we found that fungal community structure, metabolic potentials, and biogeography were jointly influenced by seasonal forces and metal stress. In summer, fungal communities were more sensitive to environmental heterogeneity, showing rapid species turnover and spatial synchrony with metal biogeographic patterns. Metals exhibited significantly broader associations with community assembly, higher network centrality and extensive correlations with metabolic potentials. Cd, Cu Co, Pb and Sr consistently emerged as key predictors. In contrast, winter communities were characterised by stronger interspecific interactions, exhibiting more universal dynamics. Fungi adopted multifunctional trophic strategies, with increased Pathotroph-Saprotroph-Symbiotroph taxa demonstrating their metabolic flexibility and resilience to metal pressures. This seasonal ecological differentiation reflected combined effects of temporal variability, spatial isolation and metal-specific filters mediated by sediment and seawater properties. These findings provide potential biomarkers and theoretical insights for assessing ecological resilience and managing metal-impacted coastal ecosystems.