Response of soil water, salt, carbon and bacteria community to terrain and plant in coastal salt marsh

Terrain and plants play a crucial role in influencing or regulating the variations of water, salt, carbon, and bacteria community in the soil of coastal salt marshes. Investigating these variations and their interconnections under different conditions is essential to comprehensively understand the carbon sequestration function and reveal the underlying mechanisms of carbon sinks in coastal salt marshes. In this study, the various physicochemical properties of rhizosphere and non-rhizosphere soil under different terrain of coastal salt marsh in Jiaozhou Bay were determined. Additionally, the contents of soil carbon components including soil inorganic carbon (SIC), soil organic carbon (SOC), dissolved inorganic carbon (DIC), and dissolved organic carbon (DOC), and constituents of soil dissolved organic matter (DOM) and microbial community were analyzed. The results showed that the contents of SIC and SOC in high-terrain soil were significantly lower than those in low-terrain soil (P < 0.05). Plants could regulate the physicochemical properties, and carbon components of soil in different terrain, resulting in no significant difference in SOC contents of rhizosphere soil under different terrain. Soil DOM composition and bacterial community showed that high-terrain soil had higher bacterial diversity and activity, and plants significantly affected the bacterial community structure in soil through rhizosphere effects. The structural equation model demonstrated that terrain has an indirect impact on SOC through influencing on the fluorescence of soil DOM and bacterial diversity, and SIC through altering soil water content (SWC), electrical conductivity and DOC. Plants directly or indirectly affected SOC content, and indirectly affected SIC content by changing SWC. This study contributes to a better understanding of the complex interactions between wetland ecosystems and their soil water, salt, carbon, and bacteria community components, offering valuable information for wetland management and conservation efforts.