Land use change affects microbial biomass and fluxes of carbon dioxide and nitrous oxide in tropical peatlands

Land use change in tropical peat soil is thought to cause intense greenhouse gas emissions by enhancing organic matter decomposition. Although microbes in peat soil play key roles in the emission of greenhouse gases, their characteristics remain unknown. This study was conducted to clarify the effect of land use change (drainage, forest fire and agricultural land use) on the control of gas emission factors with respect to the characteristics of microbes in tropical peat soils. Field observations were carried out in Central Kalimantan, Indonesia, from July 2009 to March 2011. Carbon dioxide (CO2) and nitrous oxide (N2O) fluxes in tropical peat soils were measured in an undrained natural forest, a drained forest, two burned forests and four croplands. A fumigation-extraction method was used to measure the soil microbial biomass to evaluate the relationships among the soluble organic carbon (SOC), microbial biomass carbon (MBC) and nitrogen (MBN) and the CO2 and N2O fluxes in peat soils. Regarding the relationships between weekly precipitation and N2O emission, positive relationships were found in both the forest and cropland soils. However, the slope of the regression line was much higher in the croplands than in the forest soils. The CO2 fluxes in the croplands but not in the forest soils were significantly correlated with both precipitation and N2O fluxes. In contrast, the CO2 fluxes in the forest but not in the croplands were significantly correlated with the MBC and the MBC/SOC ratio. The SOC did not show any relationship with the CO2 fluxes but showed a positive relationship with the MBN and a negative linear relationship with the nitrate (NO3-) concentration. In addition, the MBN showed a negative relationship with most of the probable numbers of ammonium oxidizers. These results indicate that the agricultural land use of tropical peat soils varied the factors controlling greenhouse gas emissions through microbial activities. Therefore, the microbial biomass may be a key factor in controlling CO2 fluxes in forest soils but not in agricultural peat soils. However, precipitation may be a key factor in agricultural peat soils but not in forest soils.