Divergent Patterns of Interactions Between Dissolved Organic Matter and Microbial Communities in Mangroves and Salt Marshes

Mangroves and salt marshes are major blue carbon reservoirs, where dissolved organic matter (DOM) dynamics are co-regulated by primary production, microbial transformation, and environmental conditions. Understanding whether these two coastal wetlands exhibit fundamentally different DOM-microbe interaction patterns is critical for assessing blue carbon functioning. However, such interactions and their environmental determinants remain unclear. Here, we conduct a continental-scale comparison between mangroves and salt marshes spanning ~5000 km of China's coastline to elucidate the linkages between DOM molecules and microbial communities. DOM and bacterial β-diversity are positively correlated in both wetlands, but their respective distance-decay relationships are significant only in salt marshes. DOM-microbe co-occurrence networks are bacteria-dominated in both wetlands, but are more complex and positively linked in mangroves, whereas negatively linked in salt marshes. DOM-gene networks show that carbon fixation and methanogenesis genes are primarily associated with recalcitrant DOM in mangroves, but with labile DOM in salt marshes. Soil pH, together with mean annual temperature, dissolved organic carbon, soil organic carbon, total nitrogen, and amorphous calcium, collectively influence the divergences in DOM composition, microbial community structure, and carbon metabolic functions. These findings offer key insights into DOM-microbe interaction mechanisms and their divergent patterns across "blue carbon" ecosystems.