Effect of Suaeda salsa on Soil Aggregate-Associated Organic Carbon and Nitrogen in Tidal Salt Marshes in the Liaohe Delta, China

In coastal wetlands, the effect of vegetation on soil organic carbon (C) quality is not clear. In this study, we investigated soil organic C and total nitrogen (N) in the whole soils, particulate organic matter (POM) and different aggregate fractions in the 0–15 and 15–30 cm layers in Suaeda salsa clusters and bare grounds in the salt marshes of the Liaohe Delta, China. S. salsa increased soil organic C, total N, POMC and POMN concentrations in both soil layers. Interestingly, the presence of S. salsa caused an increase in the amount of macroaggregates (>0.25 mm) in both 0–15 and 15–30 cm depths, whereas the vegetation effect on microaggregates (0.053–0.25 mm) and silt- and clay-sized fractions (<0.053 mm) differed with soil depth. Compared with bare grounds, S. salsa clusters had higher soil organic C and N contents at each aggregate size class. Among the three aggregate size classes, the magnitude of increases in soil organic C and N contents in the macroaggregates was the largest. Our results suggest that vegetation substantially increases the proportion of relatively labile soil organic C and contributes to soil organic C sequestration in tidal salt marshes in the Liaohe Delta, China.