Interaction effects of elevated CO2 and temperature on microbial biomass and enzyme activities in tropical rice soils

The impacts of elevated CO2 and temperature on microbial biomass and soil enzyme activities in four physicochemically different types of tropical rice soils (Aeric Endoaquept, Aeric Tropoaquept, Ultic Haplustalf and Udic Rhodostalf) were investigated in a laboratory incubation study. Soil samples were incubated under 400, 500 and 600 μmol mol − 1 CO2 concentration at 25°C, 35°C and 45°C for 2 months. Elevated CO2 significantly increased the mean microbial biomass carbon (MBC) content, across the soils, over control by 6.2%, 38.0% and 49.2% at 400, 500 and 600 μmol mol − 1 CO2 concentration, respectively. Soil enzyme activities (fluorescein diacetate hydrolase, dehydrogenase, β-glucosidase, urease, alkaline and acid phosphatases) also increased significantly ranging from 1.3% (urease) to 53.2% (alkaline phosphatase) under high CO2 in the soils studied. Both MBC and soil enzyme activities were further stimulated at high temperatures suggesting elevated CO2 and high temperature interaction accelerated the general turnover of the organic C fractions of the soil and through increase in microbially mediated processes.