Effects of natural vegetation restoration on dissolved organic matter (DOM) biodegradability and its temperature sensitivity.

Biodegradation of dissolved organic matter (DOM) plays a key role in regulating both production of greenhouse gases and accumulation and stabilisation of soil organic matter (SOM). However, the mechanisms by which natural vegetation restoration affects the extent, rate, and temperature sensitivity of DOM biodegradation are poorly understood. Elucidating these mechanisms is important for SOM management, especially in light of future climate warming scenarios. In this study, a laboratory DOM solution incubation experiment was conducted to comprehensively investigate the effects of temperature and natural vegetation restoration spanning a period of 160 y on DOM biodegradation in the Loess Plateau, China. The results indicated that dissolved organic C (DOC) biodegradation significantly decreased with vegetation restoration after an incubation period of 60 d. Further, biodegradation of dissolved organic N (DON) and dissolved organic P (DOP) significantly decreased after farmland abandonment. Specifically, the lowest values were observed in pioneer (Populus davidiana) and mingled (Populus davidiana and Quercus liaotungensis) forests. Generally, an increase in temperature significantly promoted the biodegradation of DOC, DON, and DOP by enhancing the microbial utilisation efficiencies of recalcitrant humic substrates (i.e., low-molecular-weight humic materials). Our results suggest that DOM biodegradability and its temperature sensitivity were regulated by DOM substrate quality (i.e, recalcitrant humic materials), and microbial properties (i.e., gram-negative bacterial and fungal PLFA, enzyme activities). Additionally, our results suggest that climax forest communities (Quercus liaotungensis) played a vital role in reducing DOC and DOP losses. This could be attributed to the low Q10 of the DOC and DOP biodegradation rates.