Abstract: Coastal estuarine wetlands serve as globally important carbon (C) and nitrogen (N) sinks, owing to the unique habitat heterogeneity. We investigated the spatial variations of soil C and N and their driving factors across three typical coastal habitats in the Minjiang River estuary, including salt marshes (Phragmites australis, Cyperus malaccensis, and mudflats), mangroves, and restored aquaculture wetlands. The results showed that: 1) Soils under P. australis, C. malaccensis, and mangrove wetlands exhibited higher contents of total carbon (TC), total nitrogen (TN), dissolved organic carbon (DOC), and easily oxidizable organic carbon (EOC) than those in mudflats and restored wetlands, while microbial biomass carbon (MBC) was lower in these habitats compared to mudflats and restored wetlands. The ammonium content in mudflat soils (3.82±2.02 mg·kg^-1) was significantly higher than in other habitats, whereas nitrate content (0.11±0.02 mg·kg^-1) was not different from other habitats. Across all the habitats, microbial biomass nitrogen (MBN) and MBC declined with increasing soil depth, while the C/N ratio and the MBC/MBN ratio remained relatively stable. 2) Structural equation modeling results showed that soil texture affected C and N distribution by regulating environmental factors such as moisture, bulk density, pH, electrical conductivity, and organic matter. Soil moisture, electrical conductivity, and organic matter had positive effects on the accumulation of TC and TN, whereas bulk density and pH had negative effects. Increased TC and TN further promoted the accumulation of DOC, EOC, and microbial biomass, but reduced C/N ratio.

Key words: habitat difference, carbon, nitrogen, Minjiang River Estuary wetland