Long-term bare fallow soil reveals the temperature sensitivity of priming effect of the relatively stabilized soil organic matter

Background and aims Priming effect (PE) plays an important role in modifying the decomposition of soil organic matter (SOM), but large uncertainties remain in the temperature effect on PE mainly due to the variation in SOM stability. Methods We tested the temperature effect on PE of the relatively stabilized SOM by incubating soils collected from a bare fallow (representing the relatively stabilized SOM) and its adjacent old field (containing both stabilized SOM and labile SOM) at 10 and 20 degrees C for 815 days. We used a natural C-13 abundance tracer method for measuring the PE. Results Positive PE was observed in all treatment combinations when maize leaf litter was added. The temperature sensitivity of PE in the bare fallow soil and the old field soil was quite different: increasing temperature significantly enhanced the magnitude of PE in the bare fallow soil, but had no effect on it in the old field soil. The increase of microbial biomass C by litter addition was higher in the bare fallow soil than in the old field soil. Furthermore, for litter-treated soil, temperature increase significantly increased net N mineralization rate throughout the incubation in the bare fallow soil, but had minor effect on it in the old field soil at the end of incubation. Conclusions Overall, this study demonstrates that PE of the relatively stabilized SOM is sensitive to temperature, which may be mainly driven by greater microbial growth and demand for N.