Study on spatial variation characteristics of plant-derived and microbial-derived carbon in coastal wetland soils

To clarify the spatial variation of soil organic carbon (SOC) sources in coastal wetlands, this research selected four typical coastal wetlands along a latitudinal gradient from 20°N to 40°N in eastern China, collected surface soil samples, and used amino sugars and lignin phenols as biomarkers of microbial- derived carbon and plant-derived carbon, respectively. The results showed that the contents of glucosamine (GluN), galactosamine (GalN), muramic acid (MurA), and total amino sugars all increased significantly with latitude (P < 0.01). In contrast, the contents of vanillyl phenols (V phenols), syringyl phenols (S phenols), cinnamyl phenols (C phenols), and total lignin phenols all decreased significantly with increasing latitude (P < 0.01). These opposing trends indicate that microbial-derived carbon is more likely to accumulate in high-latitude coastal wetlands, whereas plant-derived carbon plays a more important role in low-latitude coastal wetlands. In addition, the source composition of SOC exhibited a clear shift along the latitudinal gradient, with low-latitude regions being mainly dominated by plant residue inputs, while high- latitude regions gradually became dominated by the accumulation and preservation of microbial necromass. Overall, SOC formation in coastal wetlands is jointly regulated by plant inputs, microbial transformation, and necromass preservation, and the relative importance of these processes shows a clear latitudinal pattern. This research contributes to a deeper understanding of blue carbon formation mechanisms, improves the accuracy of SOC stock estimation in coastal wetlands, and provides theoretical support for the conservation, ecological restoration, and carbon management of coastal wetlands.