Rates of soil respiration components in response to inorganic and organic fertilizers in an intensively-managed Moso bamboo forest

Fertilization is a common practice to increase forest productivity; however, the responses of soil respiration (R-S) components to the application of inorganic and organic fertilizers and the associated mechanisms are not clear in subtropical forest ecosystems. In this field trial conducted within an intensively-managed Moso bamboo (Phyllostachys edulis) forest, we aimed to compare the effects of inorganic and organic fertilizers, and their combination on seasonal variations in R-S components, i.e., heterotrophic (R-H) and autotrophic (R-A) respiration, and to establish the relations of R-S components with soil properties. Fertilizer additions increased R-H (P < 0.05), with the increase being greater with organic than with inorganic fertilizer. Fertilization also increased R-A, but the effect was greater with inorganic fertilizer. Furthermore, fertilizer additions increased (P < 0.05) the concentrations of water-soluble organic C (WSOC) and microbial biomass C, invertase and beta-glucosidase activities, as well as the biomass and N concentration of fine roots. Irrespective of fertilizer treatment, strong seasonal patterns were observed in both R-S and R-H, and an exponential relation (P < 0.01) was found between R-S components (R-H and R-A) and soil temperature. Additionally, the Q10 for RH was higher (P < 0.05) in the inorganic than the organic fertilizer treatment. Although R-S and R-H showed no correlation with soil moisture content in any treatment, each of them was positively correlated with WSOC concentration and activities of invertase and beta-glucosidase (P < 0.05). In the fertilized treatments, RA was positively related to beta-glucosidase activities (P < 0.05) but not to the concentrations of WSOC or microbial biomass C. In conclusion, soil R-A and R-H in the sub-tropical Moso bamboo forest responded differently to the application of inorganic and organic fertilizers, indicating that separation of total RS into soil RH and RA is critically necessary to predict R-S in subtropical forests under different fertilizer regimes.