Abstract: To clarify the growing season dynamics of soil microbial biomass C and N in water conservation forests in the headstream of Taizi River watershed, we measured soil microbial biomass C and N in two soil layers of Larix gmeliniiplantation, natural secondary broadleaved forest, and Pinus tabuliformis plantation from April to September 2016. The relationships between soil microbial biomass and soil nutrient and soil water were analyzed. Our results showed that soil microbial biomass C and N were significantly higher in natural secondary broadleaved forest than that in both coniferous plantations (P<0.05), but all decreased gradually with increasing soil depth. The soil microbial biomass C and N in the three forests varied significantly among seasons, i.e., increased gradually in spring, peaked in summer, and decreased in autumn. The soil microbial biomass C/N in different forests ranged from 1 to 5, showing a seasonal pattern of decrease increasedecrease. Additionally, the microbial biomass C and N had a significantly positive correlation with soil organic carbon, total nitrogen, and soil water content, suggesting that these three variables were important factors affecting soil microbial biomass. The microbial biomass C and N varied among different forest types, with natural secondary broadleaved forest being most beneficial to nutrient accumulation. More attention should be paid to the protection of natural secondary forests and the transformation of the artificial plantations into natural secondary forests in the headstream of Taizi River watershed.

Key words: physiology, drought stress, Hibiscus hamabo, photosynthesis