Regulation of microbial methane production and oxidation by intermittent drainage in rice field soil

Soil drainage is one of the most promising approaches to mitigate methane (CH(4) ) emission from paddy fields. The microbial mechanism for the drainage effect on CH(4) emission, however, remains poorly understood. In the present study, we determined the effect of short (four drainages of 5-6 days each) and long drainage cycles (two drainages of 10-11 days each) on CH(4) emission and analyzed the response of the structure and abundance of methanogens and methanotrophs in a Chinese rice field soil at the DNA level. Rice biomass production was similar between drainage and the practice of continuous flooding. The rate of CH(4) emission, however, was reduced by 59% and 85% for the long and short drainage cycles, respectively. Quantitative (real-time) PCR analysis revealed that the total abundance of archaeal populations decreased by 40% after multiple drainages, indicating the inhibitory effects on methanogen growth. The structure of the methanogen community as determined by terminal restriction fragment length polymorphism analysis, however, remained unaffected by drainages, although it varied among rhizosphere, bulk and surface soils. Quantitative PCR analysis of the methanotrophic functional pmoA genes revealed that the total abundance of methanotrophs in rhizosphere soil increased two to three times after soil drainages, indicating a stimulation of methanotroph growth. The CH(4) oxidation potential in the rhizosphere soil also increased significantly. Furthermore, drainages caused a shift of the methanotrophic community, with a significantly increase of type II methanotrophic bacteria in the rhizosphere and surface soil. Thus, both inhibition of methanogens and stimulation of methanotrophs were partly responsible for the reduction of CH(4) emissions. The methanotroph community, however, appeared to react more sensitively to soil drainage compared with the methanogen community.     

Heavy-machinery traffic impacts methane emissions as well as methanogen abundance and community structure in oxic forest soils

Temperate forest soils are usually efficient sinks for the greenhouse gas methane, at least in the absence of significant amounts of methanogens. We demonstrate here that trafficking with heavy harvesting machines caused a large reduction in CH(4) consumption and even turned well-aerated forest soils into net methane sources. In addition to studying methane fluxes, we investigated the responses of methanogens after trafficking in two different forest sites. Trafficking generated wheel tracks with different impact (low, moderate, severe, and unaffected). We found that machine passes decreased the soils' macropore space and lowered hydraulic conductivities in wheel tracks. Severely compacted soils yielded high methanogenic abundance, as demonstrated by quantitative PCR analyses of methyl coenzyme M reductase (mcrA) genes, whereas these sequences were undetectable in unaffected soils. Even after a year after traffic compression, methanogen abundance in compacted soils did not decline, indicating a stability of methanogens here over time. Compacted wheel tracks exhibited a relatively constant community structure, since we found several persisting mcrA sequence types continuously present at all sampling times. Phylogenetic analysis revealed a rather large methanogen diversity in the compacted soil, and most mcrA gene sequences were mostly similar to known sequences from wetlands. The majority of mcrA gene sequences belonged either to the order Methanosarcinales or Methanomicrobiales, whereas both sites were dominated by members of the families Methanomicrobiaceae Fencluster, with similar sequences obtained from peatland environments. The results show that compacting wet forest soils by heavy machinery causes increases in methane production and release.     

稻田甲烷排放模型研究——模型及其修正

在过去十多年内 ,关于稻田甲烷排放的模拟已经进行了不少有益的探索并且开发出了数个有关的模型。模型的成功研制是准确定量估计不同区域范围内稻田甲烷排放的前提。以往大部分模型由于模拟精度不高 ,或者是其要求太多的输入参数 ,因而限制了它在大尺度范围内的广泛应用。在一个比较成熟的模型基础上 ,进行了必要的修正与扩充。增加了稻田甲烷通过气泡方式排放的模拟模块 ,并修正了原模型中关于土壤氧化还原电位变化的模拟 ,使之能适应于多种稻田水管理方式。新修正的模型 (CH4 MOD)不仅保留了原模型输入参数较少和易于获得的优点 ,而且能适应多种水稻耕作方式 ,这为进一步利用模型技术准确估计大尺度区域稻田甲烷排放提供了一种新的科学方法     

Structure and function of methanogens along a short-term restoration chronosequence in the Florida Everglades

The removal of plants and soil to bedrock to eradicate exotic invasive plants within the Hole-in-the-Donut (HID) region, part of the Everglades National Park (Florida), presented a unique opportunity to study the redevelopment of soil and the associated microbial communities in the context of short-term primary succession and ecosystem restoration. The goal of this study was to identify relationships between soil redevelopment and activity and composition of methanogenic assemblages in HID soils. Methane production potentials indicated a general decline in methanogenic activity with restoration age. Microcosm incubations strongly suggested hydrogenotrophic methanogenesis as the most favorable pathway for methane formation in HID soils from all sites. Culture-independent techniques targeting methyl coenzyme M reductase genes (mcrA) were used to assess the dynamics of methanogenic assemblages. Clone libraries were dominated by sequences related to hydrogenotrophic methanogens of the orders Methanobacteriales and Methanococcales and suggested a general decline in the relative abundance of Methanobacteriales mcrA with time since restoration. Terminal restriction fragment length polymorphism analysis indicated methanogenic assemblages remain relatively stable between wet and dry seasons. Interestingly, analysis of soils across the restoration chronosequence indicated a shift in Methanobacteriales populations with restoration age, suggesting genotypic shifts due to site-specific factors.     

Characterization of C1-metabolizing prokaryotic communities in methane seep habitats at the Kuroshima Knoll, southern Ryukyu Arc, by analyzing pmoA, mmoX, mxaF, mcrA, and 16S rRNA genes

Samples from three submerged sites (MC, a core obtained in the methane seep area; MR, a reference core obtained at a distance from the methane seep; and HC, a gas-bubbling carbonate sample) at the Kuroshima Knoll in the southern Ryuku arc were analyzed to gain insight into the organisms present and the processes involved in this oxic-anoxic methane seep environment. 16S rRNA gene analyses by quantitative real-time PCR and clone library sequencing revealed that the MC core sediments contained abundant archaea (approximately 34% of the total prokaryotes), including both mesophilic methanogens related to the genus Methanolobus and ANME-2 members of the Methanosarcinales, as well as members of the delta-Proteobacteria, suggesting that both anaerobic methane oxidation and methanogenesis occurred at this site. In addition, several functional genes connected with methane metabolism were analyzed by quantitative competitive-PCR, including the genes encoding particulate methane monooxygenase (pmoA), soluble methane monooxygenase (mmoX), methanol dehydrogenese (mxaF), and methyl coenzyme M reductase (mcrA). In the MC core sediments, the most abundant gene was mcrA (2.5 x 10(6) copies/g [wet weight]), while the pmoA gene of the type I methanotrophs (5.9 x 10(6) copies/g [wet weight]) was most abundant at the surface of the MC core. These results indicate that there is a very complex environment in which methane production, anaerobic methane oxidation, and aerobic methane oxidation all occur in close proximity. The HC carbonate site was rich in gamma-Proteobacteria and had a high copy number of mxaF (7.1 x 10(6) copies/g [wet weight]) and a much lower copy number of the pmoA gene (3.2 x 10(2) copies/g [wet weight]). The mmoX gene was never detected. In contrast, the reference core contained familiar sequences of marine sedimentary archaeal and bacterial groups but not groups specific to C1 metabolism. Geochemical characterization of the amounts and isotopic composition of pore water methane and sulfate strongly supported the notion that in this zone both aerobic methane oxidation and anaerobic methane oxidation, as well as methanogenesis, occur.     

Soil type links microbial colonization of rice roots to methane emission

Most of the methane (CH₄) emission from rice fields is derived from plant photosynthates, which are converted to CH₄. Rice cluster I (RC-1) archaea colonizing the rhizosphere were found to be the methanogens responsible for this process. Hence, RC-1 methanogens seem to play a crucial role in emission of the greenhouse gas CH₄. We determined the community composition and activity of methanogens colonizing the roots of eight different rice cultivars after growth on both Italian rice soil and river bank soil, which contained different communities of methanogenic archaea. The community composition was analyzed by terminal restriction fragment length polymorphism and cloning/sequencing of the archaeal 16S rRNA gene and the mcrA gene coding for a subunit of the methyl coenzyme M reductase. When grown on rice field soil, the methanogenic community of the different rice cultivars was always dominated by RC-1 methanogens. In contrast, roots were colonized by Methanomicrobiales when grown on river bank soil, in which RC-1 methanogens were initially not detectable. Roots colonized with Methanomicrobiales compared with RC-1 exhibited lower CH₄ production and CH₄ emission rates. The results show that the type of methanogens colonizing rice roots has a potentially important impact on the global CH₄ cycle.     

Effects of short-term drainage and aeration on the production of methane in submerged rice soil

Emission rates of CH₄ were measured in microcosms of submerged soil which were planted with rice. Drainage of the rice microcosms for 48 h resulted in drastically decreased CH₄ emission rates which only slowly recovered to the rates of the undrained controls. Drainage also resulted in drastically increased sulphate concentrations which only slowly decreased to nearly zero background values after the microcosms were submerged again. The mechanisms responsible for the decrease of CH₄ production by aeration were investigated in slurries of a loamy and a sandy Italian rice soil. Incubation of the soil slurries under anoxic conditions resulted first in the reduction of nitrate, sulphate and ferric iron before CH₄ production started. Incubation of the soil slurries for 48 h under air resulted in immediate and complete inhibition of CH₄ production. Although the soil slurries were then again incubated under anoxic conditions (N₂ atmosphere), the inhibition of CH₄ production persisted for more than 30 days. The redox potential of the soil increased after the aeration but returned within 15 days to the low values typical for CH₄ production. However, the concentrations of sulphate and of ferric iron increased dramatically after the aeration and stayed at elevated levels for the period during which CH₄ production was inhibited. These observations show that even brief exposure of the soil to O₂ allowed the production of sulphate and ferric iron from their reduced precursors. Elevated sulphate and ferric iron concentrations allowed sulphate-reducing and ferric iron-reducing bacteria to outcompete methanogenic bacteria on H₂ as common substrate. Indeed, concentrations of H₂ were decreased as long as sulphate and ferric iron were high so that the Gibbs free energy of CH₄ production from H₂/CO₂ was also increased (less exergonic). On the other hand, concentrations of acetate, the more important precursor for CH₄, were not much affected by the short aeration of the soil slurries, and the Gibbs free energy of CH₄ production from acetate was highly exergonic suggesting that acetotrophic methanogens were not outcompeted but were otherwise inhibited. Aeration also resulted in increased rates of CO₂ production and in a short-term increase of N₂O production. However, these increases were < 10% of the decreased production of CH₄ and did not represent a trade-off in terms of CO₂ equivalents. Hence, short-term drainage and aeration of submerged paddy fields may be a useful mitigation option for decreasing the emission of greenhouse gases.     

Molecular analyses of methyl-coenzyme M reductase alpha-subunit (mcrA) genes in rice field soil and enrichment cultures reveal the methanogenic phenotype of a novel archaeal lineage

The diversity of methanogen-specific methyl-coenzyme M reductase alpha-subunit (mcrA/mrtA) genes in Italian rice field soil was analysed using a combination of molecular techniques and enrichment cultures. From 75 mcrA/mrtA clones retrieved from rice field soil, 52 were related to members of the Methanosarcinaceae, Methanosaetaceae and Methanobacteriaceae. However, 19 and four clones formed two novel clusters of deeply branching mcrA sequences, respectively, which could not be affiliated to known methanogens. A new methanogen-specific fingerprinting assay based on terminal restriction fragment length polymorphism (T-RFLP) analysis of fluorescently labelled polymerase chain reaction (PCR) products allowed us to distinguish all environmental mcrA/mrtA sequences via group-specific Sau96I restriction sites. Even genes for the isoenzyme methyl-coenzyme M reductase two (mrtA) of Methanobacteriaceae present in rice field soil were represented by a unique 470 bp terminal restriction fragment (T-RF). Both cloning and T-RFLP analysis indicated a significant representation of novel environmental mcrA sequences in rice field soil (238 bp T-RF). To identify these mcrA sequences, methanogenic enrichment cultures with rice field soil as inoculum were established with H2/CO2 as substrates at a temperature of 50 degrees C, and these were monitored using molecular tools. In subsequent transfers of these enrichment cultures, cloning and T-RFLP analysis detected predominantly SSU rRNA genes of rice cluster I (RC-I), an uncultivated euryarchaeotal lineage discovered previously in anoxic rice field soil. In parallel, both mcrA cloning and T-RFLP analyses of the enrichment culture identified the more frequent cluster of novel environmental mcrA sequences as belonging to members of RC-I. Thus, we could demonstrate the genotype and phenotype of RC-I Archaea by the presence of a catabolic gene in a methanogenic enrichment culture before the isolation of pure cultures.     

中国南海北部陆坡沉积物古菌多样性及丰度分析

【目的】海洋沉积物中的古菌在全球生物地球化学循环中充当重要的角色,深入了解沉积物中古菌群落的结构及功能特征是探究海洋沉积物中古菌参与生物地球化学循环和生态学功能的基础。【方法】采用高通量测序技术,分别对南海北部陆坡不同海域(东部,西部和神狐海域的7个站位)沉积物中古菌16SrRNA基因进行Illumina Mi Seq测序。【结果】中国南海北部陆坡沉积物中古菌的主要门类是Bathyarchaeota、Thermoplasmata、Woesearchaeota(DHVEG-6)、Thaumarchaeota(Marine Group I)、Lokiarchaeota和Marine Hydrothermal Vent Group(MHVG),还存在少量的AK8、Marine Benthic Group A和Terrestrial Hot Spring Crenarchaeota Group(THSCG)等。在潜在水合物区沉积物中还发现了甲烷代谢相关古菌(Anaerobic methanotrophic archaea,ANME)类群,主要为ANME-1、ANME-2ab和ANME-2c等。甲烷代谢古菌的分布特征也从甲烷代谢保守功能基因mcr A(Methyl coenzyme-Mreductase A)的扩增中得到了验证。利用定量PCR对南海沉积物中的细菌、古菌的16SrRNA基因和mcrA基因进行了定量,发现细菌16SrRNA基因拷贝数为10~5-10~7 copies/g(湿重),古菌16SrRNA基因拷贝数为10~5-10~6 copies/g(湿重),潜在水合物区mcrA基因拷贝数为10~3-10~5 copies/g(湿重)。【结论】揭示了中国南海北部陆坡沉积物中具有丰富的微生物资源,其中古菌种类多样且丰度较高,同时发现冷泉特征古菌群落,为深入认识和理解南海沉积物中微生物丰度和古菌多样性,以及解析古菌地球化学功能奠定基础。     

Dissolved organic carbon chemistry and dynamics in contrasting forest and grassland soils

Seasonal variability in biogeochemical signatures was used to elucidate the dominant pathways of soil microbial metabolism and elemental cycling in an oligotrophic mangrove system. Three interior dwarf mangrove habitats (Twin Cays, Belize) where surface soils were overlain by microbial mats were sampled during wet and dry periods of the year. Porewater equilibration meters and standard biogeochemical methods provided steady-state porewater profiles of pH, chloride, sulfate, sulfide, ammonium, nitrate/nitrite, phosphate, dissolved organic carbon, nitrogen, and phosphorus, reduced iron and manganese, dissolved inorganic carbon, methane and nitrous oxide. During the wet season, the salinity of overlying pond water and shallow porewaters decreased. Increased rainwater infiltration through soils combined with higher tidal heights appeared to result in increased organic carbon inventories and more reducing soil porewaters. During the dry season, evaporation increased both surface water and porewater salinities, while lower tidal heights resulted in less reduced soil porewaters. Rainfall strongly influenced inventories of dissolved organic carbon and nitrogen, possibly due to more rapid decay of mangrove litter during the wet season. During both times of year, high concentrations of reduced metabolites accumulated at depth, indicating substantial rates of organic matter mineralization coupled primarily to sulfate reduction. Nitrous oxide and methane concentrations were supersaturated indicating considerable rates of nitrification and/or incomplete denitrification and methanogenesis, respectively. More reducing soil conditions during the wet season promoted the production of reduced manganese. Contemporaneous activity of sulfate reduction and methanogenesis was likely fueled by the presence of noncompetitive substrates. The findings indicate that these interior dwarf areas are unique sites of nutrient and energy regeneration and may be critical to the overall persistence and productivity of mangrove-dominated islands in oligotrophic settings.     

Activation of methanogenesis in arid biological soil crusts despite the presence of oxygen

Methanogenesis is traditionally thought to occur only in highly reduced, anoxic environments. Wetland and rice field soils are well known sources for atmospheric methane, while aerated soils are considered sinks. Although methanogens have been detected in low numbers in some aerated, and even in desert soils, it remains unclear whether they are active under natural oxic conditions, such as in biological soil crusts (BSCs) of arid regions. To answer this question we carried out a factorial experiment using microcosms under simulated natural conditions. The BSC on top of an arid soil was incubated under moist conditions in all possible combinations of flooding and drainage, light and dark, air and nitrogen headspace. In the light, oxygen was produced by photosynthesis. Methane production was detected in all microcosms, but rates were much lower when oxygen was present. In addition, the δ(13)C of the methane differed between the oxic/oxygenic and anoxic microcosms. While under anoxic conditions methane was mainly produced from acetate, it was almost entirely produced from H(2)/CO(2) under oxic/oxygenic conditions. Only two genera of methanogens were identified in the BSC-Methanosarcina and Methanocella; their abundance and activity in transcribing the mcrA gene (coding for methyl-CoM reductase) was higher under anoxic than oxic/oxygenic conditions, respectively. Both methanogens also actively transcribed the oxygen detoxifying gene catalase. Since methanotrophs were not detectable in the BSC, all the methane produced was released into the atmosphere. Our findings point to a formerly unknown participation of desert soils in the global methane cycle.     

干湿交替水分胁迫对水稻土细菌群落影响的研究

[目的]连续3次风干-湿润循环培养水稻土,在DNA和RNA水平下,探究细菌对干湿交替胁迫的响应机制,明确风干水稻土能否代替新鲜土壤进行细菌群落组成分析.[方法]针对我国江苏省常熟市水稻土,开展新鲜土壤的3次风干-湿润循环连续培养处理(每次循环中风干、湿润状态各维持7 d),在DNA和RNA水平应用16S rRNA基因高...     

Shifts in methanogen community structure and function associated with long-term manipulation of sulfate and salinity in a hypersaline microbial mat

Methanogenesis was characterized in hypersaline microbial mats from Guerrero Negro, Baja California Sur, Mexico both in situ and after long-term manipulation in a greenhouse environment. Substrate addition experiments indicate methanogenesis to occur primarily through the catabolic demethylation of non-competitive substrates, under field conditions. However, evidence for the coexistence of other metabolic guilds of methanogens was obtained during a previous manipulation of sulfate concentrations. To fully characterize methanogenesis in these mats, in the absence of competition for reducing equivalents with sulfate-reducing microorganisms, we maintained microbial mats for longer than 1 year under conditions of lowered sulfate and salinity levels. The goal of this study was to assess whether observed differences in methane production during sulfate and salinity manipulation were accompanied by shifts in the composition of methanogen communities. Culture-independent techniques targeting methyl coenzyme M reductase genes ( mcrA ) were used to assess the dynamics of methanogen assemblages. Clone libraries from mats sampled in situ or maintained at field-like conditions in the greenhouse were exclusively composed of sequences related to methylotrophic members of the Methanosarcinales . Increases in pore water methane concentrations under conditions of low sulfate correlated with an observed increase in the abundance of putatively hydrogenotrophic mcrA , related to Methanomicrobiales . Geochemical and molecular data provide evidence of a significant shift in the metabolic pathway of methanogenesis from a methylotroph-dominated system in high-sulfate environments to a mixed community of methylotrophic and hydrogenotrophic methanogens under low sulfate conditions.     

稻田土壤亚硝酸盐型甲烷厌氧氧化菌群落结构的时空特征

稻田是温室气体甲烷的重要排放源之一,对全球气候变化具有重要影响.由隶属于NC10门的Candidatus Methylomirabilis oxyfera(M.oxyfera)-like细菌介导的亚硝酸盐型甲烷厌氧氧化是控制稻田甲烷排放的新途径.目前,有关此类微生物群落在稻田土壤中的时空分布特征及其环境影响因素尚不明确...     

Seasonal variation of phenol/benzoate-degrading iron-reducing bacteria in irrigated tropical paddy soils as affected by some management practices

The study provides the first evidence of the presence and abundance of bacterial population that coupled ferric iron reduction to aromatic compounds degradation in tropical irrigated paddy soils in the Philippines. Culturable phenol/benzoate degrading iron-reducing bacteria was enumerated by the most probable number (MPN) counts using phenol or benzoate as sole carbon source, and ferric oxide [Fe(OH)(3)] as the sole electron acceptor. Population density of phenol degrading iron-reducing bacteria (P-IRB) in irrigated paddy soil ranged from 10(2) to 10(8)g(-1) dry soil, and increased with the progressive rice growth in rice cropping seasons; the study also revealed a significant rhizosphere effect on population of P-IRB. However, high enumeration of benzoate degrading iron-reducing bacteria (B-IRB) was obtained in all the tested soil samples averaging at 1.2 x 10(6)g(-1) dry soil, and did not fluctuate significantly over the rice cropping seasons. Statistical data showed that less cropping density with aerated fallow and high nitrogen rate favored the population growth of P-IRB. However, results showed that population size of B-IRB was relatively insensitive to the effect of either seasonal or extrinsic factors tested in this study.     

电子受体和光照对土壤CH4排放相关微生物功能基因丰度的影响

为探究光照条件下添加不同电子受体对土壤甲烷排放的影响及微生物的响应,本研究在土壤中添加3种电子受体(Fe3+、NO3-、SO42-)共设计8个处理,即黑暗+ Fe3+(DF)、黑暗+NO3-(DN)、黑暗+SO42-(DS)、黑暗+蒸馏水(DCK)、光照+Fe3+(LF)、光照+NO3-(LN)、光照+SO42-(LS...     

Methane-cycling communities in a permafrost-affected soil on Herschel Island, Western Canadian Arctic: active layer profiling of mcrA and pmoA genes

In Arctic wet tundra, microbial controls on organic matter decomposition are likely to be altered as a result of climatic disruption. Here, we present a study on the activity, diversity and vertical distribution of methane-cycling microbial communities in the active layer of wet polygonal tundra on Herschel Island. We recorded potential methane production rates from 5 to 40?nmol?h(-1) g(-1) wet soil at 10?°C and significantly higher methane oxidation rates reaching values of 6-10?μmol?h(-1) g(-1) wet soil. Terminal restriction fragment length polymorphism (T-RFLP) and cloning analyses of mcrA and pmoA genes demonstrated that both communities were stratified along the active layer vertical profile. Similar to other wet Arctic tundra, the methanogenic community hosted hydrogenotrophic (Methanobacterium) as well as acetoclastic (Methanosarcina and Methanosaeta) members. A pronounced shift toward a dominance of acetoclastic methanogens was observed in deeper soil layers. In contrast to related circum-Arctic studies, the methane-oxidizing (methanotrophic) community on Herschel Island was dominated by members of the type II group (Methylocystis, Methylosinus, and a cluster related to Methylocapsa). The present study represents the first on methane-cycling communities in the Canadian Western Arctic, thus advancing our understanding of these communities in a changing Arctic.     

Microbial mechanism for rice variety control on methane emission from rice field soil

Rice variety is one of the key factors regulating methane (CH₄) production and emission from the paddy fields. However, the relationships between rice varieties and populations of microorganisms involved in CH₄ dynamics are poorly understood. Here we investigated CH₄ dynamics and the composition and abundance of CH₄‐producing archaea and CH₄‐oxidizing bacteria in a Chinese rice field soil planted with three types of rice. Hybrid rice produced 50–60% more of shoot biomass than Indica and Japonica cultivars. However, the emission rate of CH₄ was similar to Japonica and lower than Indica. Furthermore, the dissolved CH₄ concentration in the rhizosphere of hybrid rice was markedly lower than Indica and Japonica cultivars. The rhizosphere soil of hybrid rice showed a similar CH₄ production potential but a higher CH₄ oxidation potential compared with the conventional varieties. Terminal restriction fragment length polymorphism analysis of the archaeal 16S rRNA genes showed that the hydrogenotrophic methanogens dominated in the rhizosphere whereas acetoclastic methanogens mainly inhabited the bulk soil. The abundance of total archaea as determined by quantitative (real‐time) PCR increased in the later stage of rice growth. However, rice variety did not significantly influence the structure and abundance of methanogenic archaea. The analysis of pmoA gene fragments (encoding the α‐subunit of particulate methane monooxygenase) revealed that rice variety also did not influence the structure of methanotrophic proteobacteria, though variable effects of soil layer and sampling time were observed. However, the total copy number of pmoA genes in the rhizosphere of hybrid rice was approximately one order of magnitude greater than the two conventional cultivars. The results suggest that hybrid rice stimulates the growth of methanotrophs in the rice rhizosphere, and hence enhances CH₄ oxidation which attenuates CH₄ emissions from the paddy soil. Hybrid rice is becoming more and more popular in Asian countries. The present study demonstrated that planting of hybrid rice will not enhance CH₄ emissions albeit a higher grain production than the conventional varieties.     

成都平原水稻-油菜轮作系统氧化亚氮排放

2005年6月—2006年6月利用静态箱/气相色谱法对成都平原水稻 油菜轮作系统氧化亚氮（N₂O）排放进行定位观测, 研究了该系统N₂O排放特征及土壤水热状况、氮肥施用、作物参与对N₂O排放的影响. 结果表明: 成都平原水稻-油菜轮作系统N₂O排放总量为（8.3±2.8）kg·hm^-2·a^-1, 水稻季、油菜季和休闲期对整个轮作周期N₂O排放总量的贡献分别为30%、65%和5%. 水稻季N₂O平均排放速率表现为排灌交替期最大, 持续淹水期和排水晒田期相当;氮肥施用是N₂O排放高峰出现的主要驱动力;土壤表层含水量偏低是旱季出现土壤N₂O吸收现象的主要原因. 土壤水分、土壤温度、施用氮肥和作物参与均在不同程度上影响N₂O排放, 土壤水分是影响N₂O排放的关键因子, 避免水稻季土壤频繁干湿交替或控制旱季土壤水分(表层土壤含水孔隙率介于50%～70%)可有效抑制N₂O排放.