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

Abstract

Fertilization is a common practice to increase forest productivity; however, the responses of soil respiration (RS) 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 RS components, i.e., heterotrophic (RH) and autotrophic (RA) respiration, and to establish the relations of RS components with soil properties. Fertilizer additions increased RH (P < 0.05), with the increase being greater with organic than with inorganic fertilizer. Fertilization also increased RA, 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 β-glucosidase activities, as well as the biomass and N concentration of fine roots. Irrespective of fertilizer treatment, strong seasonal patterns were observed in both RS and RH, and an exponential relation (P < 0.01) was found between RS components (RH and RA) and soil temperature. Additionally, the Q10 for RH was higher (P < 0.05) in the inorganic than the organic fertilizer treatment. Although RS and RH showed no correlation with soil moisture content in any treatment, each of them was positively correlated with WSOC concentration and activities of invertase and β-glucosidase (P < 0.05). In the fertilized treatments, RA was positively related to β-glucosidase activities (P < 0.05) but not to the concentrations of WSOC or microbial biomass C. In conclusion, soil RA and RH in the subtropical 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 RS in subtropical forests under different fertilizer regimes.