Soil Organic Matter Dynamics as Affected by Land Use Change from Rice Paddy to Wetland

Abstract

The objective of this study was to investigate the impact of land use change, from rice paddy to natural wetland, on soil organic matter dynamics 12 years after the former was abandoned. Cold water extracted organic carbon (CWEOC) and hot water extracted organic carbon (HWEOC) obtained from surface and subsurface soil layers were measured as important indexes, reflecting organic matter dynamics. The quality of CWEOC and HWEOC was characterized by UV absorbance and parallel factor analysis (PARAFAC) modeling of fluorescence excitation-emission matrices (FEEMs). The results showed the land use change didn’t significantly alter the quantity of SOC in all layer, but decrease the concentrations of CWEOC and HWEOC whereas the δ13C values appeared to increase. It suggested the carbon input into soil induced the change of DOC. The SUVA254 results showed aromatic content of DOC was less abundant in rice paddy, indicating DOC from paddy soil is more labile. The FEEM analysis suggested extracts from the rice paddy surface and wetland subsurface layers contain more humic-like fluorophores, while higher abundances of the tryptophan-like fluorophore were found in rice paddy subsurface and wetland surface layers. Overall, converting rice paddy to wetland didn’t alter the stock of SOC; however, it significantly decreased the stock and stability of dissolved organic carbon.