Plant community, geomorphology, and macrobenthos as drivers of spatial variations in soil carbon and nitrogen in a coastal shoal

Abstract Coastal salt marsh wetlands are crucial reservoirs of soil carbon (C) and nitrogen (N). However, the effects of plant type, geomorphology, and macrobenthos on spatial variations in soil C and N in coastal wetlands remain unclear. In this study, the spatial distribution of soil C and N components was investigated in a coastal wetland (Jiuduansha Shoal) in the Yangtze Estuary, and plant type distribution, plant biomass, soil properties, and macrobenthos species and biomass along the geomorphological gradient were measured. The results showed that the amounts and stocks of soil total C, soil organic C, soil total N, and soil microbial biomass C and N at the Spartina alterniflora (SA) and Phragmites australis (PA) sites were significantly higher than those at the bare mudflat (BM) sites. The soil and microorganism C and N variables showed a remarkable increasing trend from low- to high-elevation sites. The abundance of macrobenthos at the Scirpus mariqueter site was the highest among the plant communities and was significantly higher than that at the Zizania latifolia (ZL) and BM sites. The air-free dry weight (AFDW) of macrobenthos in the PA community was the highest among the communities. The variability in soil C and N was mainly sensitive to plant biomass, soil water content, bulk density, macrobenthos AFDW, particle size, electrical conductivity, and nutrient levels. We suggest that the synergetic effects of biotic and abiotic factors in the intertidal environment need to be fully considered in assessing and managing the C and N pools of coastal salt marshes in East China.