Carbon dynamics in submerged soil microcosms as influenced by elevated CO2and temperature

A 45-d incubation experiment was conducted under controlled laboratory cond itions to study the interactive effects of elevated CO2 and temperature on the dynamics of microbial biomass C and organic C in hooded paddy soil micr ocosms amended or unamended with rice straw. The microcosms with the two tr eatments were transferred separately to four growth chambers to incubate th em under 16 h/8 h light and dark conditions. Two of the growth chambers set at 25 and 35 degrees C provided a continuous how of elevated CO2 (equivale nt to 800 mu L L-1). Similarly the other two growth chambers were run under near ambient CO2 (400 mu L L-1) conditions at each of the two temperatures . The amounts of soluble carbon, microbial biomass C, chlorophyll-type comp ounds, and organic C in the surface (0-1 cm) and sub-surface (below 1 cm) s oil layers were measured at 15, 30, and 45 d after incubation. The amount o f soluble carbon in the straw-amended soil gradually decreased throughout t he incubation period, while no significant differences were detected among the four different conditions. The interactive effects of both elevated CO2 and temperature were found to be positive in terms of the size of the micr obial biomass in surface soil, although no significant differences were det ected in the subsurface. However, the amount of total soil organic C was la rger in the soils incubated at a lower temperature. The amounts of chloroph yll-type compounds doubled in the surface soil when the soils were incubate d under elevated CO2 conditions, indicating that the higher incubation conc entration of CO2 promoted the growth of algae in surface soil.