Nitrous oxide (N 2 O) 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 N 2 O 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 N 2 O emissions were among the highest values reported from cultivated tropical, temperate and boreal organic soils. Mean annual N 2 O 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 N 2 O emissions did not differ significantly between forests in 2002-2003, but were significantly lower in burned forest in 2003-2004. Annual N 2 O emission was significantly correlated between years. Regression analysis revealed that annual N 2 O emissions in 2003 -2004 were 1.9-fold the corresponding 2002-2003 value (annual precipitation of 2339 and 1994 mm, respectively). N 2 O fluxes were higher during the rainy season than during the dry season at all sites except the regenerated forest. N 2 O 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 NO 3 -N concentration when WFPS exceeded this threshold. Thus, changes in soil moisture were important in controlling seasonal changes in N 2 O emission. Our results suggest that changing land use from forestry to agriculture will increase N 2 O production. The effect of forest fires on N 2 O emission from these soils was not clear. N 2 O emissions from Indonesian peatlands 663

Our previous research showed large amounts of nitrous oxide (N 2 O) emission (4200 kg N ha À1 year À1 ) from agricultural peat soil. In this study, we investigated the factors influencing relatively large N 2 O fluxes and the source of nitrogen (N) substrate for N 2 O in a tropical peatland in central Kalimantan, Indonesia. Using a static chamber method, N 2 O and carbon dioxide (CO 2 ) 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 N 2 O emission from two treatments, contribution of the N source for N 2 O was calculated. Nitrous oxide concentrations at five depths (5-80 cm) were also measured for calculating net N 2 O production in soil. Annual N fertilizer application rates in the croplands ranged from 472 to 1607 kg N ha À1 year À1. There were no significant differences in between N 2 O fluxes in the two treatments at each site. Annual N 2 O emission in conventional and bare treatments varied from 10.9 to 698 and 6.55 to 858 kg N ha À1 year À1 , respectively. However, there was also no significant difference between annual N 2 O emissions in the two treatments at each site. This suggests most of the emitted N 2 O was derived from the decomposition of peat. There were significant positive correlations between N 2 O and CO 2 fluxes in bare treatment in two croplands where N 2 O flux was higher than at another cropland. Nitrous oxide concentration distribution in soil measured in the conventional treatment showed that N 2 O was mainly produced in the surface soil down to 15 cm in the soil. The logarithmic value of the ratio of N 2 O flux and nitrate concentration was positively correlated with water filled pore space (WEPS). These results suggest that large N 2 O emission in agricultural tropical peatland was caused by denitrification with high decomposition of peat. In addition, N 2 O was mainly produced by denitrification at high range of WFPS in surface soil.

Using a soilless culture system mimicking tropical acidic peat soils, which contained 3 mg of gellan gum and 0.5 mg NO3−-N per gram of medium, a greenhouse gas, N2O emitting capability of microorganisms in acidic peat soil in the area of Palangkaraya, Central Kalimantan, Indonesia, was investigated. The soil sampling sites included a native swamp forest (NF), a burnt forest covered by ferns and shrubs (BF), three arable lands (A-1, A-2 and A-3) and a reclaimed grassland (GL) next to the arable lands. An acid-tolerant Janthinobacterium sp. strain A1-13 (Oxalobacteriaceae, β-proteobacteria) isolated from A-1 soil was characterized as one of the most prominent N2O-emitting bacteria in this region. Physiological characteristics of the N2O emitter in the soilless culture system, including responses to soil environments, substrate concentration, C-source concentration, pH, and temperature, suggest that the N2O emitting Janthinobacterium sp. strain A1-13 is highly adapted to reclaimed open peatland and primarily responsible for massive N2O emissions from the acidic peat soils. Regulation of N2O emitters in the reclaimed peatland for agricultural use is therefore one of the most important issues in preventing the greenhouse gas emission from acidic peat soil farmlands

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 m 3 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 lowintermediate 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 Mg 2+ 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.

To clarify the microbiological factors that explain high N 2 O emission in an arable peat soil in Central Kalimantan, Indonesia, a substrate-induced respiration-inhibition experiment was conducted for N 2 O production. The N 2 O 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 N 2 O 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 N 2 O-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 N 2 O-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% CO 2 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 N 2 O-producing potential and the growth potential in conditions of low O 2 concentration.