Seasonal changes of microbial biomass carbon related to climatic factors in soils from karst areas of southwest China

The seasonal responses of soil microbial biomass C to changes in atmospheri c temperature, soil moisture and soluble organic C were studied in soils fr om the karst areas of southwest China. These soils are relatively weathered , leached and impoverished, and have a low input of plant residues. Over 1 year, an inverse relationship between soil microbial biomass C and atmosphe ric temperature was found. The highest microbial biomass C occurred in wint er and the lowest in summer, and ranged from 231-723 mu g g(-1) dry soil. A lthough there was no obvious relationship between microbial biomass C and s oil moisture, a negative correlation existed between microbial biomass C an d soluble organic C. In the ecosystem studied, the marked changes in soil m icrobial biomass C at above 20 degrees C were ascribed to fluctuations of s oil moisture, which were controlled by climatic factors and geomorphic cond itions. The patterns of soluble organic C turnover were similar to those of soluble carbohydrate C, both of which were controlled by soil drying-rewet ting cycles. It was concluded that the lowest amounts of soil microbial bio mass C, measured in the summer, resulted in increases in soluble organic C due to higher turnover rates of the former at warmer air temperatures. Thus , there was a marked seasonal change in soil microbial biomass C.