Linking soil dissolved organic matter characteristics and the temperature sensitivity of soil organic carbon decomposition in the riparian zone of the Three Gorges Reservoir

Soil dissolved organic matter (DOM) is highly sensitive to external interference. However, little attention has been paid on how soil DOM characteristics in the dry period affect the warming response of soil organic carbon (SOC) decomposition in riparian ecosystems under flooding conditions. The temperature sensitivity (Q(10)) of SOC decomposition was determined by incubating 99 riparian soils under flooding across 11 transects of the Three Gorges Reservoir. Soil DOM characteristics in the dry period were measured by ultraviolet-visible spectroscopy (i.e., a254, a350, SUVA254 and SR) and 3D-fluorescence spectroscopy (such as FI, beta:alpha, BIX, and HIX). The fluorescence components of C1, C3, and C4 were determined by parallel factor analysis. SOC decomposition was sensitive to warming with a higher Q10 value for CH4 (2.34 +/- 1.30) and lower for CO2 (1.37 +/- 0.23) under flooding. The soil DOM in dry period was mainly autochthonous with FI > 1.9 and 90% of BIX > 0.7. The humification of soil DOM was relatively weak at similar to 95% of HIX < 0.8. The Q(10) value of CO2 was positively correlated with Ln (SUVA254) and Ln (HIX) whereas negatively correlated with Ln (DOC), Ln (a254), and Ln (a350). The Q(10) of CH4 was positively related to Ln (HIX), while on the contrary, negatively related to Ln (C4). These variations in Q(10) were mainly driven by the aromaticity and humification degree of DOM. Out of all DOM characteristics, the lignin component was the key predictor of the Q(10) variation. Overall, findings of this study indicate that soil DOM characteristics in dry period are closely linked with the response of SOC decomposition to warming during the reservoir impoundment.