[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.以中亚热带常绿阔叶林及由其改造而来的闽楠、毛竹及杉木人工林为研究对象,采用氯仿熏蒸浸提法测定了4种林分类型表层(0～10 cm)和深层(40～60 cm)土壤微生物生物量碳(MBC)和氮(MBN),并分析了其季节变化及与土壤理化性质之间的关系.结果表明: 4种林分类型表层土壤MBC和MBN均以常绿阔叶林最高,其次为闽楠人工林、毛竹人工林和杉木人工林,且前三者显著高于后者;各林分深层土壤MBC和MBN无显著差异.4种林分类型的表层土壤MBC和MBN均显著高于深层土壤,且各土层MBC和MBN均具有明显的季节变化,总体呈现出“夏高冬低”单峰曲线变化模式.相关分析表明,4种林分类型土壤MBC和MBN与土壤有机碳、全氮及土壤温度呈显著正相关关系,与土壤容重呈显著负相关关系.表明常绿阔叶林改造成人工林30多年后,表层土壤MBC和MBN呈下降趋势,其中杉木人工林下降幅度最大(分别下降39.0%和49.8%),而对深层土壤MBC和MBN的影响较小.凋落物数量和质量、土壤有机碳和总氮含量及土壤温度是导致各林分类型土壤微生物生物量碳氮差异和季节变化的主要因素.