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

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We previously demonstrated that xanthobaccin A from the rhizoplane bacterium Lysobacter sp. strain SB-K88 suppresses damping-off disease caused by Pythium sp. in sugar beet. In this study we focused on modes of Lysobacter sp. strain SB-K88 root colonization and antibiosis of the bacterium against Aphanomyces cochlioides, a pathogen of damping-off disease. Scanning electron microscopic analysis of 2-week-old sugar beet seedlings from seeds previously inoculated with SB-K88 revealed dense colonization on the root surfaces and a characteristic perpendicular pattern of Lysobacter colonization possibly generated via development of polar, brush-like fimbriae. In colonized regions a semitransparent film apparently enveloping the root and microcolonies were observed on the root surface. This Lysobacter strain also efficiently colonized the roots of several plants, including spinach, tomato, Arabidopsis thaliana, and Amaranthus gangeticus. Plants grown from both sugar beet and spinach seeds that were previously treated with Lysobacter sp. strain SB-K88 displayed significant resistance to the damping-off disease triggered by A. cochlioides. Interestingly, zoospores of A. cochlioides became immotile within 1 min after exposure to a SB-K88 cell suspension, a cell-free supernatant of SB-K88, or pure xanthobaccin A (MIC, 0.01 g/ml). In all cases, lysis followed within 30 min in the presence of the inhibiting factor(s). Our data indicate that Lysobacter sp. strain SB-K88 has a direct inhibitory effect on A. cochlioides, suppressing damping-off disease. Furthermore, this inhibitory effect of Lysobacter sp. strain SB-K88 is likely due to a combination of antibiosis and characteristic biofilm formation at the rhizoplane of the host plant.

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