Role of Iron in Stabilization of Soil Organic Carbon Under Different Vegetation Communities of Mangrove Wetlands

Abstract

Iron (Fe) oxides play an important role in maintaining soil organic carbon (SOC) stability. However, little attention has been paid to the role of Fe oxides in preserving SOC in mangrove wetlands with different vegetation communities. In this study, four soils of dominant vegetation communities: Phragmites australis (PA), Acanthus ilicifolius (AI), Sonneratia apetala (SA), and mixed soils of S. apetala and A. ilicifolius (SA + AI) were selected from mangrove wetland of Qi'ao Island. The distributions of Fe‐bound organic carbon (OC‐Fe) and Fe oxides (Feo, acid oxalate‐extractable Fe; Fep, pyrophosphate‐extractable Fe), and the role of soil factors in SOC conservation were investigated. The results showed that soil OC‐Fe content ranged from 1.03 to 4.96 g/kg, with a contribution to SOC ranging from 5.97% to 24.07%, which was highest in SA + AI (3.58 ± 0.94 g/kg), followed by PA (2.67 ± 1.07 g/kg), SA (1.88 ± 0.43 g/kg), and AI (1.82 ± 0.32 g/kg). The Fep content was higher in the PA and SA + AI, however, the Feo content was lower. Structural equation modeling indicated that SOC, Feo, and Fep were direct drivers of OC‐Fe formation. Overall, the aboveground biomass of different vegetation communities indirectly affected the OC‐Fe content by regulating SOC inputs. High water contents, low oxygen conditions, and near‐neutral soils in mangrove wetlands favor OC‐Fe formation between Fe oxides and SOC by co‐precipitation or complexation. This study highlights the importance of mangrove wetland vegetation communities in Fe‐C coupling, while providing theoretical support for the study of carbon cycling processes in mangrove wetlands.