Abstract: The mineralization of soil organic carbon (SOC) plays an important role in soil carbon and nitrogen cycling. Inputs of labile organic C can stimulate or mitigate SOC mineralization through positive or negative priming effect. While previous studies on the effects of the amount of labile organic carbon input on soil priming effect focused more on the topsoil, less attention has been paid to the deep soil. We carried out a ¹³C labeling experiment to investigate the effects of labile organic carbon input on the priming effect at topsoil and subsoil layers which were collected from an evergreen broadleaved forest in Wuyi Mountain. We examined the changes in microbial community composition and soil available N content to clarify the underlying mechanisms. The results showed that the input of glucose inhibited SOC mineralization (i.e., a negative priming effect), but the priming magnitude  varied across different amounts of glucose input and soil depths. The magnitude increased with the amount of glucose input for topsoil, but remained stable in deep soil. Moreover, glucose input had no significant effect on soil microbial biomass and community composition (i.e., total PLFA content, bacteria, fungi, actinomycetes, and the ratio of bacteria to fungi). The magnitude of priming effect was not dependent on the amount of glucose input and microbial community composition, but dependent on soil available nitrogen content, which accounted for 90.8% and 63.4% of the variation in the magnitude of priming effect for the topsoil and subsoil, respectively. Glucose input led to a decline in soil available N, but was not associated with microbial N immobilization, indicating that soil available N can meet microbial demands. The negative priming effect observed in this study might be attributed to preferential substrate utilization.

Key words: soil phosphorus fraction, harvest residue, soil organic phosphorus, Chinese fir plantation