Hironori Arai

Effect of soil types and nitrogen fertilizer on nitrous oxide and carbon dioxide emissions in oil palm plantations

Abstract Oil palm (Elaeis guineensis Jacq.) production in Indonesia and Malaysia is currently the focus of concern due to its potential impact on the environment via greenhouse gas emissions. Oil palm plantations have been reported to release large quantities of nitrous oxide (N2O) into the atmosphere, which is most likely linked to nitrogen (N) fertilizer use. However, there are still limited studies comparing effects of the type of soil and N fertilizer on N2O and carbon dioxide (CO2) emissions. This study aimed to evaluate the effects of soil types and N fertilizer on N2O and CO2 emissions in oil palm plantations. N2O and CO2 emissions were measured for 15–16 months from 2010–2012 in Tunggal sandy loam soil, Indonesia, and in Simunjan sandy soil and Tatau peat soil, Malaysia. Within each site, treatments with coated fertilizer and conventional fertilizer, and unfertilized with and without tillage, were established. N2O and CO2 fluxes showed high variabilities with seasons, types of soil and fertilizer treatments. The mean of the N2O fluxes from each treatment in the Simunjan sandy soil was the lowest among the three soils, ranging from 0.80 to 3.81 and 1.63 to 5.34 μg N m−2 h−1 in the wet and dry seasons, respectively. The mean of the N2O fluxes from each treatment in the Tunggal sandy loam soil ranged from 27.4 to 89.7 and 6.27 to 19.1 μg N m−2 h−1 in the wet and dry seasons, respectively. The mean of the N2O fluxes was found to be the highest among the three soils in each treatment of the Tatau peat soil, ranging from 131 to 523 and 66.1 to 606 μg N m−2 h−1 in the wet and dry seasons, respectively. The N application rate of coated fertilizer was about half that of conventional fertilizer and was applied as deep placement. In the Tungal soil, coated fertilizer reduced N2O emissions by 31 and 48% in wet and dry seasons, respectively, compared to the conventional fertilizer, and was similar to unfertilized treatment. However, N2O emissions increased in Simunjan and Tatau soils during dry seasons. There was no significant difference between treatments. These results show that N2O and CO2 fluxes in the tropical oil palm plantations were significantly affected by the type of soil, but not always by fertilizer treatments.

A methanotrophic community in a tropical peatland is unaffected by drainage and forest fires in a tropical peat soil

Abstract The effects of drainage and forest fires on the methanotrophic activity and community structure of peat soils in a tropical forest were studied by analyzing methane fluxes and the population of methanotrophs. A denaturing gradient gel electrophoresis (DGGE) analysis was used to target particular methane monooxygenase genes (pmoA). An incubation experiment was performed to investigate methane production activity relative to the effects of flooding and litter fall. Low levels of methane fluxes were observed in the soils in drained forest, natural forest and burned forest sites. These fluxes did not differ significantly among the sites (–0.02 ± 0.01–0.36 ± 0.30 mg C m−2 hr−1). The water-filled pore space (WFPS) showed a statistically significant positive relationship with methane fluxes and a statistically significant negative relationship with the populations of methanotrophs. A DGGE profile targeted on pmoA gene fragments showed no apparent differences in the gene patterns among the various soil types. Four of the excised bands showed identical sequences closely related to type 1 methanotrophs, Methylomonas spp. An incubation experiment showed stronger methane oxidation than methane production in the absence of litter, even under flooded conditions. These results indicated that labile organic carbon or intact photosynthetic products, such as litter, may act as the principal substrate for methane production in the flooded condition and that the recalcitrant woody organic matter preserved under flooded anaerobic conditions in the peat soils for a long period would, most likely, play only a subordinate role. Under these environmental conditions, the methanotrophic community may consist primarily of type 1 methanotrophs irrespective of drainage and forest fires, and its activity could be controlled by WFPS by adjusting the oxygen supply to the peat soils.

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

Abstract 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.

Effect of oxidizing and reducing agents in soil on methane production in Southeast Asian paddies

ABSTRACT Methane is one of the greenhouse gases emitted from paddy soil ecosystems and may induce global warming and climate change; therefore, mitigation options are urgently required to establish mitigation technology to reduce methane emission without affecting rice production. Methane is produced by a balance between oxidizing agents (such as iron) and reducing agents (easily decomposable soil organic matter), according to the so-called Takai theory. To evaluate options for mitigating methane production potential and to examine the applicability of the Takai theory in Southeast Asian paddy soils, 23 soil samples were collected from Thailand, Indonesia, Philippines, and Vietnam. These soil samples were anaerobically incubated to measure their methane production potential and examined to see whether their chemical properties, such as the ferrous, total iron, and organic matter contents, were correlated. We found a significant negative correlation between the methane production potential and the total iron content, and a positive correlation between the methane production potential and the hexose content, as an index for a soil’s easily decomposable organic matter content. The methane–C/CO2–C production ratio was also positively correlated with the mineralizable nitrogen/ferrous contents ratio, which indicated that the Takai theory, established for Japanese paddy soils, is also useful in Southeast Asian paddy soils and that the soil’s iron content is important to estimate the methane production potential.

Estimation of Methane Emissions from Rice Paddies in the Mekong Delta Based on Land Surface Dynamics Characterization with Remote Sensing

In paddy soils in the Mekong Delta, soil archaea emit substantial amounts of methane. Reproducing ground flux data using only satellite-observable explanatory variables is a highly transparent method for evaluating regional emissions. We hypothesized that PALSAR-2 (Phased Array type L-band Synthetic Aperture RADAR) can distinguish inundated soil from noninundated soil even if the soil is covered by rice plants. Then, we verified the reproducibility of the ground flux data with satellite-observable variables (soil inundation and cropping calendar) and with hierarchical Bayesian models. Furthermore, inundated/noninundated soils were classified with PALSAR-2. The model parameters were successfully converged using the Hamiltonian–Monte Carlo method. The cross-validation of PALSAR-2 land surface water coverage (LSWC) with several inundation indices of MODIS (Moderate Resolution Imaging Spectroradiometer) and AMSR-2 (Advanced Microwave Scanning Radiometer-2) data showed that (1) high PALSAR-2-LSWC values were detected even when MODIS and AMSR-2 inundation index values (MODIS-NDWI and AMSR-2-NDFI) were low and (2) low values of PALSAR-2-LSWC tended to be less frequently detected as the MODIS-NDWI and AMSR-2-NDFI increased. These findings indicate the potential of PALSAR-2 to detect inundated soils covered by rice plants even when MODIS and AMSR-2 cannot, and show the similarity between PALSAR-2-LSWC and the other two indices for nonvegetated areas.

Function of the methanogenic community in mangrove soils as influenced by the chemical properties of the hydrosphere

ABSTRACT Coastal ecosystems represent a potential additional source of the greenhouse gas methane (CH4) that has been insufficiently quantified. Thus, to understand the mechanisms controlling greenhouse gas emissions in these ecosystems, this study investigated CH4 emissions from and the related microbial properties of mangrove soils. Soil and gas samples were collected from several plots at different distances from the seashore in Soc Trang and Ca Mau in Vietnam, and the Sundarbans in India. Soil samples were incubated under different conditions, i.e., anaerobic or aerobic, and the microbial properties of each soil sample with the addition of different amounts of seawater were analyzed. Relatively high CH4 fluxes and production were detected during the aerobic incubation of samples from the seashore plots in Soc Trang and Ca Mau. However, CH4 production was reduced under anaerobic conditions [soil electrical conductivity (EC): 179–289 mS m−1, pH (H2O): 7.45–8.10] compared with aerobic conditions [water content: 38.9–109.2%, EC: 187–299 mS m−1, pH (H2O): 6.86–7.72], but it increased with increasing sulfate concentration, soil EC and cellulase activity and lowering soil pH under anaerobic conditions. Furthermore, mangrove soil with a relatively high level of total organic carbon (C) exhibited relatively high CH4 production when diluted 4-fold with seawater under anaerobic conditions [water content: 38.9–109.2%, EC: 533 mS m−1, pH (H2O): 6.67]. Nearly all of the DNA bands excised from polymerase chain reaction-denaturing gradient gel electrophoresis contained identical sequences related to archaea from the class Halobacteria. The high potential of the seashore plot for CH4 emissions could be due to the enhancement of cellulase activity under the intermittent oxygen supply, which promotes polysaccharide depolymerization and subsequently increases anaerobic methanogenic activities during tidal flooding. This study also indicates that the major archaea responsible for CH4 production require a particular hydrospheric salt concentration and soil pH.

Methane and Nitrous Oxide Emissions from Tropical Peat Soil

Results of observations in Central Kalimantan, Indonesia clearly indicate that land use changes caused by drainage, fire, and agricultural practices change the methane (CH4) and nitrous oxide (N2O) emissions from tropical peatlands significantly. The CH4 emissions were higher in burned area and croplands than in natural forests. The N2O emissions were considerably higher in croplands than in natural forests, although there were no significant differences in N2O emissions between burned areas and natural forests. In croplands, the N2O flux was significantly correlated with the carbon dioxide (CO2) flux. However, the CO2 flux in croplands was not correlated with microbial biomass carbon (MBC), while this was significantly correlated in forests. These results indicate that agricultural land use of tropical peatlands varied the controlling factors of the greenhouse gas emissions through microbial activities. Peat fires were also a significant source of CH4 and N2O as well as CO2. Linear correlations of the concentrations of CH4, N2O, and also carbon monoxide (CO) to CO2 indicated that the molar ratios of CO, CH4 and N2O to CO2 in the gas emissions through peat combustion are 0.382, 0.0261 and 0.000156, respectively.