Soil-Aggregate-Associated Organic Carbon Along Vegetation Zones in Tidal Salt Marshes in the Liaohe Delta

In the tidal salt marshes, the spatial variation of soil carbon (C) quality along the vegetation zones is still unclear. Here, a study is conducted in the mudflat, open shrubland, and dense shrubland in the Liaohe Delta, Northeast China, and soil organic C (OC) stock, particulate organic matter C (POMC), and aggregate-associated OC in the 0-15 and 15-30 cm depths are investigated along these vegetation zones. Among the three vegetation zones, dense shrubland had the greatest soil OC stock, open shrubland had the lowest value, and mudflat had an intermediate value. In each soil depth, dense shrubland generally had higher soil OC and POMC concentrations, and POMC/OC ratio compared to mudflat and open shrubland, respectively. Moreover, dense shrubland had a greater proportion of macro-aggregates (>0.25 mm in diameter) and OC content in the macro-aggregates than mudflat and open shrubland, respectively. In addition, the OC content in the soil macro-aggregates positively correlated with soil POMC concentration. These results suggest that the high spatial variability in soil OC quantity and quality along the vegetation zones should be incorporated to accurately develop regional C budget in coastal wetlands in the Liaohe Delta, and also imply that a shift in vegetation zones induced by sea level rise could potentially cause substantial changes in the quantity and quality of soil OC in the tidal salt marshes.