Combination of potential methanogenesis and microbial respiration as a scalar to determine the microbial biomass in submerged rice paddy soils

Both aerobic and anaerobic microbes are responsible for the fertility of soils by mineralizing organic matter. In water-logged soils, like rice paddy soils, anaerobic microbes have a great importance in the mineralization. We developed a method to determine microbial biomass in rice paddy soils by combining of anaerobic and aerobic microbial processes as a scalar for the microbial biomass. Potential methanogenesis was used to describe the anaerobic microbial community, while substrate-induced respiration (SIR) is related to the aerobic microbes. The calibration of the method was based on the total microbial biomass determined by fumigation extraction (FE) method. Microbial biomass carbon (MBC) could be calculated using the following equation: MBC = kcf (1.956 MA + 0.710 SIR + 10.192), where kcf = 2.142 ± 0.337 (coefficient based on the calibration against FE), MA = potential methanogenesis and SIR = substrate induced respiration. The MBC had shown significantly positive correlation (r = 0.830*) with the total C loss potential or C mineralization potential (μg C loss g−1 soil d−1) [={MA × (12/16)} + {SIR × (12/44)}] of rice paddy soils.