Abstract: The rhizosphere is an important site for the exchange of matter and energy between trees and the external environment. It is of great significance to explore rhizosphere soil microorganisms and their stoichiometric characteristics for understanding nutrient cycling in forest ecosystems. In this study, the contents of carbon (SOC), nitrogen (TN) and phosphorus (TP) in rhizosphere and bulk soil under dry and wet seasons were measured in 10-year-old pure forest of Cunninghamia lanceolata (PCL), pure forest of Phoebe bournei (PPB) and mixed forest of Cunninghamia lanceolata and Phoebe bournei (MCP), and the rhizosphere effects of ecological stoichiometry were analyzed. The results showed that the contents of SOC, TN, TP, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and microbial biomass phosphorus (MBP) in rhizosphere soil under the three forest types were generally higher than those in bulk soil. The contents of SOC, TN, TP, MBC, MBN and MBP in rhizosphere soil of Cunninghamia lanceolata and Phoebe bournei in mixed forest were significantly lower than those of pure Cunninghamia lanceolata and Phoebe bournei plantations, respectively. Soil C∶N, C∶P and N∶P in PCL stand were significantly higher than those in PPB. The MBC∶MBN and MBC∶MBP of rhizosphere and bulk soils increased significantly in dry season after mixed with Phoebe bournei, and these ratios of rhizosphere and bulk soils of Phoebe bournei decreased significantly after mixing with Cunninghamia lanceolata. The activity of rhizosphere soil sucrase was higher in mixed forest than in pure forest in both seasons. The activity of catalase in mixed rhizosphere soil was significantly lower than that in bulk soil. Results of partial least squares path analysis showed that mixed planting had negative effects on soil microbial biomass and rhizosphere effect, with a greatest rhizosphere effect on MBP. Mixed cultivation had overall positive effect on soil pH.

Key words: microbial biomass, rhizosphere soil, nutrient cycling, soil enzyme