Changes in CO2, 13C abundance, inorganic nitrogen, β-glucosidase, and oxidative enzyme activities of soil during the decomposition of switchgrass root carbon as affected by inorganic nitrogen additions

This study was conducted to investigate the effect of inorganic nitrogen (N) and root carbon (C) addition on decomposition of organic matter (OM). Soil was incubated for 200 days with nine treatments (three levels of N (no addition (N0) = 0, low N (NL) = 0.021, high N (NH) = 0.083 mg N g(-1) soil) x three levels of C (no addition (C0) = 0, low C (CL) = 5, high C (CH) = 10 mg root g(-1) soil)). The carbon dioxide (CO2) efflux rates, inorganic N concentration, pH, and potential activities of beta-glucosidase and oxidative enzyme were measured during incubation. At the beginning and the end of incubation, the native soil organic carbon (SOC) and root-derived SOC were quantified by using a natural labeling technique based on the differences in delta C-13 between C3 and C4 plants. Overall, the interaction between C and N was not significant. The decomposition of OM in the NH treatment decreased. This could be attributed to the formation of recalcitrant OM by N because the potentially mineralizable C pool was significantly lower in the NH treatment (3.1 mg C g(-1)) than in the N0 treatment (3.6 mg C g(-1)). In root C addition treatments, the CO2 efflux rate was generally in order of CH > CL > C0 over the incubation period. Despite no differences in the total SOC concentration among C treatments, the native SOC in the CH treatment (18.29 mg C g(-1)) was significantly lower than that in the C0 treatment (19.16 mg C g(-1)).