Untung Darung

Effects of agricultural land-use change and forest fire on N2O emission from tropical peatlands, Central Kalimantan, Indonesia

Abstract Nitrous oxide (N2O) fluxes from tropical peatland soils were measured at a grassland, three croplands, a natural forest, a burned forest and a regenerated forest in Central Kalimantan, Indonesia. Only croplands received fertilization (665–1278 kg N ha−1 year−1). Mean annual N2O emissions from croplands were 21–131 kg N ha−1 year−1 in 2002–2003 and 52–259 kg N ha−1 year−1 in 2003–2004, and were significantly higher than the emissions from other comparable sites. Cropland N2O emissions were among the highest values reported from cultivated tropical, temperate and boreal organic soils. Mean annual N2O emissions were 7.1 (2002–2003) and 23 (2003–2004) kg N ha−1 year−1 from grassland, and were significantly higher than in natural, regenerated and burned forests (0.62, 0.40 and 0.97 kg N ha−1 year−1 in 2002–2003 and 4.4, 4.0 and 1.5 kg N ha−1 year−1 in 2003–2004, respectively). Annual N2O emissions did not differ significantly between forests in 2002–2003, but were significantly lower in burned forest in 2003–2004. Annual N2O emission was significantly correlated between years. Regression analysis revealed that annual N2O emissions in 2003–2004 were 1.9-fold the corresponding 2002–2003 value (annual precipitation of 2339 and 1994 mm, respectively). N2O fluxes were higher during the rainy season than during the dry season at all sites except the regenerated forest. N2O fluxes in cropland and grassland were significantly lower when the water-filled pore space (WFPS) was less than 60–70%, and increased with an increase in soil NO3–N concentration when WFPS exceeded this threshold. Thus, changes in soil moisture were important in controlling seasonal changes in N2O emission. Our results suggest that changing land use from forestry to agriculture will increase N2O production. The effect of forest fires on N2O emission from these soils was not clear.

Fungal N2O production in an arable peat soil in Central Kalimantan, Indonesia

Abstract To clarify the microbiological factors that explain high N2O emission in an arable peat soil in Central Kalimantan, Indonesia, a substrate-induced respiration-inhibition experiment was conducted for N2O production. The N2O emission rate decreased by 31% with the addition of streptomycin, whereas it decreased by 81% with the addition of cycloheximide, compared with a non-antibiotic-added control. This result revealed a greater contribution of the fungal community than bacterial community to the production of N2O in the soil. The population density of fungi in the soil, determined using the dilution plate method, was 5.5 log c.f.u. g−1 soil and 4.9 log c.f.u. g−1 soil in the non-selective medium (rose bengal) and the selective medium for Fusarium, respectively. The N2O-producing potential was randomly examined in each of these isolates by inoculation onto Czapek agar medium (pH 4.3) and incubation at 28°C for 14 days. Significant N2O-producing potential was found in six out of 19 strains and in five out of seven strains isolated from the non-selective and selective media, respectively. Twenty-three out of 26 strains produced more than 20% CO2 during the 14-day incubation period, suggesting the presence of facultative fungi in the soil. These strains were identified to be Fusarium oxysporum and Neocosmospora vasinfecta based on the sequence of 18S rDNA, irrespective of the N2O-producing potential and the growth potential in conditions of low O2 concentration.

Nitrous oxide emission derived from soil organic matter decomposition from tropical agricultural peat soil in central Kalimantan, Indonesia

Our previous research showed large amounts of nitrous oxide (N2O) emission (>200 kg N ha−1 year−1) from agricultural peat soil. In this study, we investigated the factors influencing relatively large N2O fluxes and the source of nitrogen (N) substrate for N2O in a tropical peatland in central Kalimantan, Indonesia. Using a static chamber method, N2O and carbon dioxide (CO2) fluxes were measured in three conventionally cultivated croplands (conventional), an unplanted and unfertilized bare treatment (bare) in each cropland, and unfertilized grassland over a three-year period. Based on the difference in N2O emission from two treatments, contribution of the N source for N2O was calculated. Nitrous oxide concentrations at five depths (5–80 cm) were also measured for calculating net N2O production in soil. Annual N fertilizer application rates in the croplands ranged from 472 to 1607 kg N ha−1 year−1. There were no significant differences in between N2O fluxes in the two treatments at each site. Annual N2O emission in conventional and bare treatments varied from 10.9 to 698 and 6.55 to 858 kg N ha−1 year−1, respectively. However, there was also no significant difference between annual N2O emissions in the two treatments at each site. This suggests most of the emitted N2O was derived from the decomposition of peat. There were significant positive correlations between N2O and CO2 fluxes in bare treatment in two croplands where N2O flux was higher than at another cropland. Nitrous oxide concentration distribution in soil measured in the conventional treatment showed that N2O was mainly produced in the surface soil down to 15 cm in the soil. The logarithmic value of the ratio of N2O flux and nitrate concentration was positively correlated with water filled pore space (WEPS). These results suggest that large N2O emission in agricultural tropical peatland was caused by denitrification with high decomposition of peat. In addition, N2O was mainly produced by denitrification at high range of WFPS in surface soil.

Effect of plant-mediated oxygen supply and drainage on greenhouse gas emission from a tropical peatland in Central Kalimantan, Indonesia

Abstract To evaluate the hypothesis that plant-mediated oxygen supplies decrease methane (CH4) production and total global warming potential (GWP) in a tropical peatland, the authors compared the fluxes and dissolved concentrations of greenhouse gases [GHGs; CH4, carbon dioxide (CO2) and nitrous oxide (N2O)] and dissolved oxygen (DO) at multiple peatland ecosystems in Central Kalimantan, Indonesia. Study ecosystems included tropical peat swamp forest and degraded peatland areas that were burned and/or drained during the rainy season. CH4 fluxes were significantly influenced by land use and drainage, which were highest in the flooded burnt sites (5.75 ± 6.66 mg C m−2 h−1) followed by the flooded forest sites (1.37 ± 2.03 mg C m−2 h−1), the drained burnt site (0.220 ± 0.143 mg C m−2 h−1), and the drained forest site (0.0084 ± 0.0321 mg C m−2 h−1). Dissolved CH4 concentrations were also significantly affected by land use and drainage, which were highest in the flooded burnt sites (124 ± 84 μmol L−1) followed by the drained burnt site (45.2 ± 29.8 μmol L−1), the flooded forest sites (1.15 ± 1.38 μmol L−1) and the drained forest site (0.860 ± 0.819 μmol L−1). DO concentrations were influenced by land use only, which were significantly higher in the forest sites (6.9 ± 5.6 μmol L−1) compared to the burnt sites (4.0 ± 2.9 μmol L−1). These results suggest that CH4 produced in the peat might be oxidized by plant-mediated oxygen supply in the forest sites. CO2 fluxes were significantly higher in the drained forest site (340 ± 250 mg C m−2 h−1 with a water table level of −20 to −60 cm) than in the drained burnt site (108 ± 115 mg C m−2 h−1 with a water table level of −15 to +10 cm). Dissolved CO2 concentrations were 0.6–3.5 mmol L−1, also highest in the drained forest site. These results suggested enhanced CO2 emission by aerobic peat decomposition and plant respiration in the drained forest site. N2O fluxes ranged from −2.4 to −8.7 μg N m−2 h−1 in the flooded sites and from 3.4 to 8.1 μg N m−2 h−1 in the drained sites. The negative N2O fluxes might be caused by N2O consumption by denitrification under flooded conditions. Dissolved N2O concentrations were 0.005–0.22 μmol L−1 but occurred at < 0.01 μmol L−1 in most cases. GWP was mainly determined by CO2 flux, with the highest levels in the drained forest site. Despite having almost the same CO2 flux, GWP in the flooded burnt sites was 20% higher than that in the flooded forest sites due to the large CH4 emission (not significant). N2O fluxes made little contribution to GWP.

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 groundwater level fluctuation on soil respiration rate of tropical peatland in Central Kalimantan, Indonesia

ABSTRACT Soil respiration (SR) rate was measured at the burned land (BL), the cropland (CL), the forest land (FL) and the grassland (GL) of a tropical peatland in Central Kalimantan, Indonesia from 2002 to 2011 for the purpose of analysis with a relation to the drying and rewetting. The SR rate was fitted with groundwater level (GWL) to the equation of log(SR) = α – β × GWL using hierarchical Bayesian analysis where α and β were regression coefficients classified by GWL changing directions (drying, rewetting and fluctuating), water-filled pore space (WFPS) ranges in topsoil (low 0–0.54, intermediate 0.54–0.75 and high 0.75–1 m3 m−3), and land uses (BL, CL, FL and GL). SR rate (Mean ± SD, mg C m−2 h−1) was the significantly largest in the CL (333 ± 178) followed by GL (259 ± 151), FL (127 ± 69) and lastly BL (100 ± 90). In the CL, the significantly larger SR rate was found in the rewetting period than in the drying period in the high WFPS range. Also, the significantly steeper slope (β) in the rewetting period was obtained in the high WFPS range than in the drying period. These results suggested that the rewetting of peatland enhanced the SR rate rapidly in the CL, and that the further rise of GWL decreased the SR rate. In contrast, the SR rate in the rewetting period was significantly smaller than in the drying period in the BL in the high WFPS range, because the BL in the high WFPS range was flooded in most cases. The SR rate in the rewetting period was not significantly different from the drying period in the FL and GL. All of β were significant in the high WFPS range in all land uses, but not in the low–intermediate WFPS ranges, suggesting that GWL was not controlling factor of the SR rate when the GWL was deep due to the disconnection of capillary force under dry conditions. According to the results of correlation analysis of the α and β, the α was significantly correlated with relative humidity, soil temperature and soil pH, suggesting that the α was enhanced by dry condition, high soil temperature and neutralization of soil acidity, respectively. The β was significantly correlated with exchangeable Na+ and Mg2+ in the soil, but the reason was not clear. In conclusion, SR rate was enhanced by rising GWL with rewetting in the CL in the high WFPS ranges as well as by deepening GWL.

Microclimate of Developed Peatland of the Mega Rice Project in Central Kalimantan

Land Characteristics of Batang Pelepat Watershed In Bungo District, Jambi (Sunarti): Land characteristics describe biophysics characteristics of watershed. But, land has been used for economic oriented. The objective of this research is to identify land characteristics of Batang Pelepat watershed. Data collection was carried out by survey based on land unit map and analyzed by descriptive analysis. The results showed that land in Batang Pelepat watershed consist of 23 land units and some land use types (forest, rubber and oil palm farming, settlement and shrub), soil parent materials variously (alluvium, granite, tuff andesite, basalt, and clay rock), soil depth ranges from 88 to 160 cm and soil texture is classified moderate fine to fine. Lands were dominated by slope of >15–30% and >45–65% and dystrudepts of soil group with soil fertility level very low to low because its pH about 3.80-6.20, base saturation about 7.86-32.79% and P- available about 2.80-25.00 ppm. Various land use has also caused different erosion and permeability levels.