Mitigating methane emissions and global warming potential while increasing rice yield using biochar derived from leftover rice straw in a tropical paddy soil.

The sustainable management of leftover rice straw through biochar production to mitigate CH4 emissions and enhance rice yield remains uncertain and undefined. Therefore, we evaluated the effects of using biochar derived from rice straw left on fields after harvest on greenhouse gas emissions, global warming potential (GWP), and rice yield in the paddy field. The experiment included three treatments: chemical fertilizer (CF), rice straw (RS, 10 t ha-1) + CF, and rice straw-derived biochar (BC, 3 t ha-1 based on the amount of product remaining after pyrolysis) + CF. Compared with CF, BC + CF significantly reduced cumulative CH4 and CO2 emissions, net GWP, and greenhouse gas emission intensity by 42.9%, 37.4%, 39.5%, and 67.8%, respectively. In contrast, RS + CF significantly increased cumulative CH4 emissions and net GWP by 119.3% and 13.8%, respectively. The reduced CH4 emissions were mainly caused by the addition of BC + CF, which did not increase the levels of dissolved organic carbon and microbial biomass carbon, consequently resulting in reduced archaeal abundance, unlike those observed in RS + CF. The BC + CF also enhanced soil total organic carbon content and rice grain yield. This study indicated that using biochar derived from leftover rice straw mitigates greenhouse gas emissions and improves rice productivity in tropical paddy soil.

Response of Methanogenic Microbial Communities to Desiccation Stress in Flooded and Rain-Fed Paddy Soil from Thailand.

Rice paddies in central Thailand are flooded either by irrigation (irrigated rice) or by rain (rain-fed rice). The paddy soils and their microbial communities thus experience permanent or arbitrary submergence, respectively. Since methane production depends on anaerobic conditions, we hypothesized that structure and function of the methanogenic microbial communities are different in irrigated and rain-fed paddies and react differently upon desiccation stress. We determined rates and relative proportions of hydrogenotrophic and aceticlastic methanogenesis before and after short-term drying of soil samples from replicate fields. The methanogenic pathway was determined by analyzing concentrations and δ13C of organic carbon and of CH4 and CO2 produced in the presence and absence of methyl fluoride, an inhibitor of aceticlastic methanogenesis. We also determined the abundance (qPCR) of genes and transcripts of bacterial 16S rRNA, archaeal 16S rRNA and methanogenic mcrA (coding for a subunit of the methyl coenzyme M reductase) and the composition of these microbial communities by T-RFLP fingerprinting and/or Illumina deep sequencing. The abundances of genes and transcripts were similar in irrigated and rain-fed paddy soil. They also did not change much upon desiccation and rewetting, except the transcripts of mcrA, which increased by more than two orders of magnitude. In parallel, rates of CH4 production also increased, in rain-fed soil more than in irrigated soil. The contribution of hydrogenotrophic methanogenesis increased in rain-fed soil and became similar to that in irrigated soil. However, the relative microbial community composition on higher taxonomic levels was similar between irrigated and rain-fed soil. On the other hand, desiccation and subsequent anaerobic reincubation resulted in systematic changes in the composition of microbial communities for both Archaea and Bacteria. It is noteworthy that differences in the community composition were mostly detected on the level of operational taxonomic units (OTUs; 97% sequence similarity). The treatments resulted in change of the relative abundance of several archaeal OTUs. Some OTUs of Methanobacterium, Methanosaeta, Methanosarcina, Methanocella and Methanomassiliicoccus increased, while some of Methanolinea and Methanosaeta decreased. Bacterial OTUs within Firmicutes, Cyanobacteria, Planctomycetes and Deltaproteobacteria increased, while OTUs within other proteobacterial classes decreased.

Methanogenic pathway and archaeal communities in three different anoxic soils amended with rice straw and maize straw.

Addition of straw is common practice in rice agriculture, but its effect on the path of microbial CH(4) production and the microbial community involved is not well known. Since straw from rice (C3 plant) and maize plants (C4 plant) exhibit different δ(13)C values, we compared the effect of these straw types using anoxic rice field soils from Italy and China, and also a soil from Thailand that had previously not been flooded. The temporal patterns of production of CH(4) and its major substrates H(2) and acetate, were slightly different between rice straw and maize straw. Addition of methyl fluoride, an inhibitor of acetoclastic methanogenesis, resulted in partial inhibition of acetate consumption and CH(4) production. The δ(13)C of the accumulated CH(4) and acetate reflected the different δ(13)C values of rice straw versus maize straw. However, the relative contribution of hydrogenotrophic methanogenesis to total CH(4) production exhibited a similar temporal change when scaled to CH(4) production irrespectively of whether rice straw or maize straw was applied. The composition of the methanogenic archaeal communities was characterized by terminal restriction fragment length polymorphism (T-RFLP) analysis and was quantified by quantitative PCR targeting archaeal 16S rRNA genes or methanogenic mcrA genes. The size of the methanogenic communities generally increased during incubation with straw, but the straw type had little effect. Instead, differences were found between the soils, with Methanosarcinaceae and Methanobacteriales dominating straw decomposition in Italian soil, Methanosarcinaceae, Methanocellales, and Methanobacteriale in China soil, and Methanosarcinaceae and Methanocellales in Thailand soil. The experiments showed that methanogenic degradation in different soils involved different methanogenic population dynamics. However, the path of CH(4) production was hardly different between degradation of rice straw versus maize straw and was also similar for the different soil types.

Removal of lead (Pb(2+)) by the cyanobacterium Gloeocapsa sp.

Pb(2+) removal ability of the viable-freshwater cyanobacterium Gloeocapsa sp. was studied in batch experiments. Gloeocapsa sp. was cultured in the Medium 18 with pH adjusted to 3, 4, 5, 6 and 7. Growth was subsequently determined based on the increase of chlorophyll-a content. Gloeocapsa sp. was able to grow at all pH levels tested, except at pH 3. Removal of Pb(2+) was then further studied under pH 4. The results showed that Pb(2+) concentration in the range of 0-20 mg L(-1) was not inhibitory to Gloeocapsa sp. growth but reduced its Pb(2+) removal efficiency (by 4.5% when Pb(2+) concentration increased from 2.5 to 20 mg L(-1)). Pb(2+) removal characteristics followed the Langmuir adsorption isotherm with the maximum removal capacity (q(max)) of 232.56 mg g(-1). Adsorption of Pb(2+) by this cyanobacterium followed the second order rate reaction and intraparticle diffusion was likely the rate-determining step. The initial rate of Pb(2+)adsorption during intraparticle diffusion was slower under light than under dark conditions, indicating that light probably slowed down the initial rate of intraparticle diffusion through the repulsion effects on cell membrane.

Methylocystis heyeri sp. nov., a novel type II methanotrophic bacterium possessing 'signature' fatty acids of type I methanotrophs.

A novel species is proposed for two strains of methanotrophic bacteria (H2(T) and Sakb1) isolated from an acidic (pH 4.3) Sphagnum peat bog lake (Teufelssee, Germany) and an acidic (pH 4.2) tropical forest soil (Thailand), respectively. Cells of strains H2(T) and Sakb1 were aerobic, Gram-negative, non-motile, straight or curved rods that were covered by large polysaccharide capsules and contained an intracytoplasmic membrane system typical of type II methanotrophs. They possessed both a particulate and a soluble methane monooxygenase and utilized the serine pathway for carbon assimilation. They were moderately acidophilic organisms capable of growth between pH 4.4 and 7.5 (optimum 5.8-6.2). The most unique characteristic of these strains was the phospholipid fatty acid profile. In addition to the signature fatty acid of type II methanotrophs (18 : 1omega8c), the cells also contained large amounts of what was previously considered to be a signature fatty acid of type I methanotrophs, 16 : 1omega8c. The DNA G+C contents of strains H2(T) and Sakb1 were 61.5 and 62.1 mol%, respectively. The 16S rRNA gene sequences possessed 96-98 % similarity to sequences of other type II methanotrophs in the genera Methylosinus and Methylocystis. 16S rRNA gene sequence and pmoA phylogeny demonstrated that the strains form a novel lineage within the genus Methylocystis. DNA-DNA hybridization values of strain H2(T) with Methylocystis parvus OBBP(T) and Methylocystis echinoides IMET 10491(T) were 18 and 25 %, respectively. Thus, it is proposed that these two strains represent a novel species, Methylocystis heyeri sp. nov. Strain H2(T) (=DSM 16984(T)=VKM B-2426(T)) is the type strain.

Production, composition and Pb2+ adsorption characteristics of capsular polysaccharides extracted from a cyanobacterium Gloeocapsa gelatinosa.

Pb2+ adsorption by the living cells of the cyanobacterium Gloeocapsa gelatinosa was studied. Cyanobacterial cells with intact capsular polysaccharide (CPS) showed 5.7 times higher Pb adsorption capacity than that of cells without CPS. The adsorbed Pb was desorbed by EDTA, indicating that Pb2+ adsorption occurred mainly on cell surface. Production, sugar content and ability of CPS to remove Pb2+ were then studied in details. CPS production by G. gelatinosa increased when culture time was prolonged. The maximum CPS production was 35.43 mg g(-1) dry weight after 30-day cultivation. Xylose, arabinose, ribose, rhamnose, galactose, glucose, mannose and fructose were the neutral sugars presented in CPS of G. gelatinosa. Acidic sugars including galacturonic and glucuronic acids were also found in CPS. The amount and composition of G. gelatinosa's CPS varied according to its growth phase and culture conditions. The highest amount of acidic sugars was produced when cultured under low light intensity. The extracted CPS rapidly removed Pb2+ from the solution (82.22+/-4.82 mg Pb2+ per g CPS), directly demonstrating its roles in binding Pb2+ ions. Its ability to remove Pb2+ rapidly and efficiently, to grow under sub-optimal conditions (such as low pH and low light intensity), and to produce high amount of CPS with acidic sugars, leads us to conclude that G. gelatinosa is a potential viable bioadsorber for mildly acidic water contaminated with Pb2+.

Diversity of methanotrophic bacteria in tropical upland soils under different land uses.

Three upland soils from Thailand, a natural forest, a 16-year-old reforested site, and an agricultural field, were studied with regard to methane uptake and the community composition of methanotrophic bacteria (MB). The methane uptake rates were similar to rates described previously for forest and farmland soils of the temperate zone. The rates were lower at the agricultural site than at the native forest and reforested sites. The sites also differed in the MB community composition, which was characterized by denaturing gradient gel electrophoresis (DGGE) of pmoA gene fragments (coding for a subunit of particulate methane monooxygenase) that were PCR amplified from total soil DNA extracts. Cluster analysis based on the DGGE banding patterns indicated that the MB communities at the forested and reforested sites were similar to each other but different from that at the farmland site. Sequence analysis of excised DGGE bands indicated that Methylobacter spp. and Methylocystis spp. were present. Sequences of the "forest soil cluster" or "upland soil cluster alpha," which is postulated to represent organisms involved in atmospheric methane consumption in diverse soils, were detected only in samples from the native forest and reforested sites. Additional sequences that may represent uncultivated groups of MB in the Gammaproteobacteria were also detected.

Three-year monitoring results of nitrate and ammonium wet deposition in Thailand.

Wet deposition is one of the important sources of nitrogen input into the ecosystem. It also contributes to rain acidity in some environments. In this study we reported the annual as well as seasonal trends of nitrogen wet deposition at three locations in Thailand: Bangkok, Chiang Mai and Nan. Comparison of nitrogen wet deposition between in rural and in the urban areas was also made. Daily rainfall was measured and monthly rainwater was collected for nitrogen analysis during 1999-2002. The average NO3- concentration in rainwater collected from the rural sites (60 km from urban area) was around 0.2-0.3 mg L(-1), while that from the urban areas of Chiang Mai and Nan cities it was 0.4-0.5 mg L(-1). NH4+ concentration in rainwater showed the similar ranges to that of NO3-, except at Nan where concentration was not significantly different between the urban and rural sites. On the other hand, the average concentrations of NO3- were higher at Bangkok site than other sites, while concentration of NH4+ was almost the same between Chiang Mai and Bangkok. Wet deposition of NO3- at the rural sites of Chiang Mai and Nan ranged from 2.1 to 3.2 kg N ha(-1) yr(-1), while at the urban sites this ranged from about 6 kg N ha(-1) yr(-1) in Chiang Mai and Nan Cities to 8.6 kg N ha(-1) yr(-1) in Bangkok. Wet deposition of NH4+ at the rural sites of Chiang Mai and Nan was about 2.4 to 3.6 kg N ha(-1) yr(-1) and at the urban sites of Chiang Mai, Nan and Bangkok this was 7.7, 4.9 and 8.1 kg N ha(-1) yr(-1), respectively. Thus, it was concluded that wet deposition of both nitrogen species was significantly higher at the urban sites than at the rural sites.