Microbial biomass carbon and methane oxidation influenced by rice cultivars and elevated CO2 in a Japanese paddy soil

Microbial biomass carbon (C) and methane oxidation activity influenced by rice cultivars and elevated atmospheric CO2 were investigated in a microcosm experiment in two controlled-environment chambers with CO2 concentrations at 370 mu l l-1 (ambient) and 570 mu l l-1 (elevated). Four rice cultivars were grown in sandy paddy soil in this experiment; these were IR65598, IR72, Dular and Koshihikari. Soil microbial biomass C under elevated CO2 was significantly larger (by 18.9-25.2%) than that under ambient CO2, and varied with the cultivars in the sequence IR72 > Dular > IR65598 > Koshihikari. Methane oxidation activity in the soil also differed among the cultivars, in the sequence IR72 > Dular > Koshihikari > IR65598, but was larger under elevated CO2 than under ambient CO2 only with IR72. Methane oxidation activity was positively correlated with microbial biomass C among four cultivars under two CO2 conditions. This study indicated that microbial biomass C in paddy soil varied among the rice varieties examined, but was increased significantly by elevated CO2 and correlated with methane oxidation, which may in turn influence methane emission to the atmosphere.