The role of dissolved organic matter in soil organic carbon stability under water erosion

Dissolved organic matter (DOM) can respond rapidly to external interference and is of great importance to soil carbon cycling. However, little information is available about the characteristics of DOM in response to water erosion and its role in soil organic carbon (SOC) stability. To contribute this area, a typical watershed in the Southern Red Soil Hilly Region was studied and soil samples were collected from two contrasting sites (eroding versus depositional sites). The DOM concentration and spectral characteristics, SOC stability and their relationships were determined. Results showed that DOM concentration in the deposited topsoil (0-5 cm, 0.69 g kg(-1)) was significantly higher than that in the eroded soil (0.27 g kg(-1)). Dissolved organic matter rich in aromatic, hydrophobic and high molecular weight moieties were concentrated in the eroded topsoil rather than in the deposited topsoil. Three fluorescent components in DOM were finally identified: tryptophan-like (C1), humic-like (C2) and protein-like (C3) components. The humic-like C2 in the eroded topsoil was significantly higher than that of the deposited topsoil (P < 0.05). The largest cumulative CO2-C (23.29 mg CO2-C kg(-1) soil d(-1)) was found in the deposited soil of 0-5 cm and it was approximately three times as high as that of the eroded soil. Regression analyses showed that the cumulative CO2 was significantly and positively related to the DOM concentration in two sites, and remarkably negatively correlated with the abundance of aromatic, hydrophobic, high molecular weight and humic-like substances in DOM. Our results indicated that the DOM was strongly affected by water erosion and can be an effective indicator for predicting the SOC stability feedback to erosion.