Effect of vegetations and temperature on microbial biomass carbon and metabolic quotients of temperate volcanic forest soils

The response of soil carbon availability and microbial utilization efficiency to varying vegetations and to increasing temperature emphasizes the need for further research in volcanic forest soils. We have studied responses of soil microbial biomass C (MBC) concentrations and metabolic quotients (qCO2, CO2-C / biomass-C) to vegetations and temperature in temperate volcanic forest soils. Soils were sampled in April and October 2003 beneath four forest stands in close proximity (200 m apart) in central Japan: a Japanese cedar coniferous forest (CI), a pine coniferous forest (CII), and an oak-dominated hardwood on a grading and steep slope (DI and DII). The soil MBC concentrations and qCO2 values beneath each forest stand were measured under oxic conditions, along with the effect of temperature and the long-term storage at low temperature on both variables. Comparing different forest stands, it was indicated that the pine forest soil always showed the lowest MBC concentration relative to soil total C, and the largest qCO2 (P < 0.05), suggesting that microbial communities in the soil were less efficient in C use than communities in the other forest soils. Under a same oak-dominated hardwood, a steep terrain induced a lower soil respiration and MBC concentration, but qCO2 values of both soils had no significant differences at 25 °C. The MBC concentration in the soils beneath each forest stand mostly had no differences during two sampling periods. The low-temperature storage induced an increase in soil MBC and a reduction of CO2 production, reducing the qCO2. There was a smaller MBC concentration in the CII soil than in the CI and DII soil within the range of 5 to 35 °C; the MBC concentration and qCO2 in the DI and CII soil appeared more sensitive at increasing temperature than those in the DII and CI soil. From the results obtained, it can be concluded that under similar climatic conditions and soil types, the MBC concentrations and qCO2 values of temperate volcanic forest soils vary with tree species and temperature, and that the high soil C-to-N ratios and low acidity can contribute to decreased soil MBC concentration and to increased qCO2.