Effects of the interaction between temperature and revegetation on the microbial degradation of soil dissolved organic matter (DOM) – A DOM incubation experiment

DOM is the most bioavailable organic pool in the soil. The restoration of vegetation on abandoned cropland has a major impact on the concentration and composition of the DOM and thus affects the biodegradability of the soil DOM. Understanding the response of the microbial degradation of the DOM to temperature is important to maintain soil bioavailable organic matter in the field. We conducted a laboratory DOM solution incubation experiment to examine the temporal dynamics of DOM concentrations at temperatures of 4 °C (low), 20 °C (medium), and 35 °C (high) for four types of land uses: sloped cropland, grassland, shrub land, and woodland. Ultraviolet–visible and fluorescence spectroscopy were used to determine the structural complexity of the DOM. The conversion of the sloped cropland to shrub land and woodland significantly increased contents of DOC, DON, and recalcitrant substances in DOM soilution, such as humic-like material and fulvic acid, and stabilised the DOC pool, and reduced the decomposition of the DOC at 20 °C and 35 °C. The conversion of the sloped cropland to woodland dramatically reduced TDN decomposition. The DON loss after 60-day incubation significantly correlated with the initial content of tryptophan-like material. The biodegradability of the DON was higher and more sensitive to temperature than that of the DOC. Rising temperature initially promotes the decomposition of tryptophan-like material, and later promotes the degradation of more recalcitrant substances, such as humic-like material and fulvic acid, which enhanced the decomposition of the DOC and DON. The results suggest that the conversion of sloped cropland to shrubland and woodland not only promoted the accumulation of DOC, TDN, and recalcitrant substances in DOM solution, and decreased their biodegradability but also decreased the temperature sensitivity of the decomposition of the DOC and DON. Therefore, shrubland and woodland were the optimal choices for revegetation in the Loess Plateau of China.