[Characteristics of soil microbial biomass carbon and nitrogen and its seasonal dynamics in four mid-subtropical forests].

Taking evergreen broad-leaved forest in mid-subtropical areas, and its converted Phoebe bournei, Phyllostachys heterocycla and Cunninghamia lanceolata plantations as research objects, microbial biomass carbon (MBC) and nitrogen (MBN) in the surface (0-10 cm) and deep soil layer (40-60 cm) were measured by chloroform fumigation and extraction method, with their seasonal dynamics and the relationships with soil physicochemical properties in four types of forests being investigated. The results showed that the MBC and MBN in the surface soil was the highest in the evergreen broad-leaved forest, followed by P. bournei, P. heterocycla and C. lanceolata plantations, with that in the former three being significantly higher than in C. lanceolata plantion. There was no significant difference in the MBC and MBN contents in the deep soil layer among the four types of forests, while those in surface soil were significantly higher than in the deep soil layer. The MBC and MBN contents showed obvious seasonal dynamics, with highest values in summer and lowest in winter presenting a single peak change pattern. MBC and MBN had significantly positive correlations with soil total carbon (TC), total nitrogen (TN) and temperature, but significantly negative correlation with soil bulk density. The conversion of evergreen broad-leaved forest to the three plantation resulted in lower MBC and MBN in the surface soil to some degree, with C. lanceolata plantation being the first to be affected, but little change occurred in the deep soil layer. The quantity and quality of litter, contents of TC, TN and soil temperature were the key factors driving the differences of MBC and MBN contents and their seasonal dynamics of the four types of forests.