Mechanisms of plant-derived and microbial residue carbon in coastal wetland soils in response to salinity gradients

Abstract

Soil Organic Carbon (SOC) is mainly categorized into plant-derived carbon (C) and microbial residue carbon. However, the accumulation characteristics of plant-derived C and microbial residue carbon in coastal wetland soils and their contributions to SOC remain unclear. Therefore, we conducted a new study on the variation of plant-derived C and microbial residual C in wetland soils of the Yellow River Delta, including four vegetation types along the salinity gradient: reed meadows, tidal flats reeds, tamarisks, and alkali poncho, by using lignin phenolics and aminoglycans as markers of plant-derived C and microbial residual C, respectively. In the soil, plant-derived C was the primary contributor of soil organic carbon. The ratio of plant-derived C to microbial-derived C increased with decreasing salinity from 1.62 to 3.97. The ratio of cinnamyl to vanillin (C:V) in reed meadow and alkali poncho communities was 0.43 and 0.12, respectively, and the acid-formaldehyde ratios of vanillin (Ac:Alv) were 0.41 and 1.13, respectively, which indicated that microbial transformations of plant-derived C were less in low-salinity soils. This study confirms that decreased salinity in coastal wetlands preferentially promotes plant-derived C accumulation to increase C storage in the topsoil, resulting in plant-derived C becoming the main contributor to SOC storage, and Particulate Organic C (POC) and Mineral-Associated Organic C (MAOC) storage being closely related to plant-derived and microbial-derived C accumulation, respectively. This provides an essential theoretical basis for the study of carbon sequestration mechanism in coastal wetlands.