Abstract:Soil microbe activity is the most important decomposer in forest ecosystems and is a sensitive indicator of environmental changes. It plays a crucial role in wetland carbon and nitrogen cycles. However, few studies on soil microbial biomass carbon and nitrogen have been conducted in the Zhalong wetland, especially studies of the seasonal dynamics of soil microbial biomass carbon and nitrogen in different habitats. In this study, in order to investigate the soil fertility of different habitats based on the soil microbial biomass, the soil microbial biomass C and N were observed in three soil layers (0-10 cm, 10-20 cm, 20-30 cm) of a reed habitat and meadow habitat in the Zhalong wetland. Meanwhile, the relationships between the soil microbial biomass and soil environmental factors were also analyzed. The experimental design included two habitat types with three 20 m × 20 m plots in each habitat type. In each plot, we took random soil samples in three soil layers (0-10 cm, 10-20 cm, and 20-30 cm) from five spots every month from May to September, 2010. The samples in each plot were mixed to produce a combined sample for soil microbial biomass carbon and nitrogen determination. All soil samples were stored at 2 ℃ before analysis within one week of sampling. The results showed that the microbial biomass C and N for different habitats displayed a vertical distribution in decreasing order of 0-10 cm > 10-20 cm > 20-30 cm. In addition, the microbial biomass C and N in the meadow habitat was greater than that of the reed habitat. During the whole growing season, the microbial biomass C and N in the two habitats showed a "W" shaped variation pattern. The variation profiles of the two habitats decreased with soil depth, but the variation in meadow habitat was significantly larger than that in the reed habitat. However, the correlation analysis showed the soil microbial biomass C in the reed habitat had an extremely significant positive correlation with the soil water content (P < 0.01) and had an extremely significant negative correlation with soil pH value (P < 0.01). The soil microbial biomass N in the reed habitat had an extremely significant positive correlation with soil water content, organic carbon and hydrolysable nitrogen (P < 0.01) and had an extremely significant negative correlation with soil pH value (P < 0.01). The soil microbial biomass C in the meadow habitat had an extremely significant positive correlation with soil water content, organic carbon, available phosphorus, hydrolysable nitrogen (P < 0.01) and had a significant positive correlation with soil pH value (P < 0.05). The soil microbial biomass N in the meadow habitat had an extremely significant positive correlation with soil water content and available phosphorus (P < 0.01) and had a significant positive correlation with organic carbon (P < 0.05). We concluded that the variations in litterfall amount and composition, and the soil physical and chemical properties among the different habitat types mainly contributed to the differences in the seasonal dynamics of the soil microbial biomass C and N in the Zhalong Wetland.