Priming effects of soil organic matter decomposition with addition of different carbon substrates

The addition of organic substrates can change the decomposition rate of soil organic matter (SOM), which is termed as “priming effect.” The objective of this study was to explore the priming effects of SOM decomposition with the addition of different organic carbon substrates, including glucose, oxalic acid, and tannin. We hypothesized that with additions from labile to recalcitrant carbon substrates, the soil priming effects changed from positive to negative. Representing from labile to recalcitrant carbon substrates, glucose, oxalic acid, and tannin were added to soil, respectively. Physicochemical properties of soil, carbon dioxide emission rate, soil organic carbon in the labile and recalcitrant carbon pools, microbial biomass carbon (MBC), and microbial community diversity and structure were measured in different treatments. Results showed that the addition of glucose and tannin produced positive priming effects, while the addition of oxalic acid led to a negative priming effect. The addition of glucose and tannin significantly increased the MBC. The addition of glucose significantly promoted the carbon decomposition in both the labile and recalcitrant soil carbon pools. The addition of tannin greatly promoted carbon decomposition in the labile carbon pool and slightly decreased carbon decomposition in the recalcitrant carbon pool of the soil. However, the addition of oxalic acid reduced the MBC and resulted in insignificant changes of the different soil carbon pools. The addition of organic carbon substrates reduced the soil microbial community diversity, especially the addition of glucose. The different priming effects of the treatments with glucose and tannin were attributable to the different phases in the succession of SOM decomposition processes. The treatment with oxalic acid reduced the soil pH, resulting in inactive microbial growth and reproduction. The addition of both glucose (labile carbon) and tannin (recalcitrant carbon) produced positive priming effects. In contrast, the addition of oxalic acid produced a negative priming effect. Except the treatment with tannin, the hypothesis was successfully tested. The results from this study should be useful to better understand the turnover processes of soil carbon pools with exogenous carbon inputs.