Influence of vegetation types and soil properties on microbial biomass carbon and metabolic quotients in temperate volcanic and tropical forest soils

Abstract There is limited knowledge about the differences in carbon availability and metabolic quotients in temperate volcanic and tropical forest soils, and associated key influencing factors. Forest soils at various depths were sampled under a tropical rainforest and adjacent tea garden after clear-cutting, and under three temperate forests developed on a volcanic soil (e.g. Betula ermanii and Picea jezoensis, and Pinus koraiensis mainly mixed with Tilia amurensis, Fraxinus mandshurica and Quercus mongolica), to study soil microbial biomass carbon (MBC) concentration and metabolic quotients (qCO2, CO2-C/biomass-C). Soil MBC concentration and CO2 evolution were measured over 7-day and 21-day incubation periods, respectively, along with the main properties of the soils. On the basis of soil total C, both CO2 evolution and MBC concentrations appeared to decrease with increasing soil depth. There was a maximal qCO2 in the 0–2.5 cm soil under each forest stand. Neither incubation period affected the CO2 evolution rates, but incubation period did induce a significant difference in MBC concentration and qCO2 in tea soil and Picea jezoensis forest soil. The conversion of a tropical rainforest to a tea garden reduced the CO2 evolution and increased the qCO2 in soil. Comparing temperate and tropical forests, the results show that both Pinus koraiensis mixed with hardwoods and rainforest soil at less than 20 cm depth had a larger MBC concentration relative to soil total C and a lower qCO2 during both incubation periods, suggesting that microbial communities in both soils were more efficient in carbon use than communities in the other soils. Factor and regression analysis indicated that the 85% variation of the qCO2 in forest soils could be explained by soil properties such as the C:N ratio and the concentration of water soluble organic C and exchangeable Al (P < 0.001). The qCO2 values in forest soils, particularly in temperate volcanic forest soils, decreased with an increasing Al/C ratio in water-soluble organic matter. Soil properties, such as exchangeable Ca, Mg and Al and water-soluble organic C:N ratio, were associated with the variation of MBC. Thus, MBC concentrations and qCO2 of the soils are useful soil parameters for studying soil C availability and microbial utilization efficiency under temperate and tropical forests.