Rate of accumulation and emission of N2, N2O and CH4 from a flooded rice soil

In a field experiment using microplots, a flooded Crowley silt loam (Typic Albaqualfs) rice soil was fertilized with ¹⁵N labelled (60–74 atom %) urea and KNO₃. Emission of N₂, N₂O and CH₄ and accumulation in soil were measured for 21 d after fertilizer application.Emission of ¹⁵N₂-N measured from the urea and KNO₃ treated plots ranged from <15 to 570 and from 330 to 3,420 g ha^–1 d^–1, respectively. Entrapped ¹⁵N₂-N in the urea treated microplots was significantly lower (<15 g to 2.1 kg ha^–1) on all sampling dates compared to the ¹⁵N₂-N gas accumulation in the KNO₃ treated plots (6.4 to 31.5 kg ha^–1). Emissions of N₂O-N were low and did not exceed 4 g ha^–1 d^–1. Fluxes of CH₄ from the fertilizer and control plots were low and never exceeded 33 g ha^–1 d^–1. Maximum accumulation of CH₄ in the flooded soil measured 460 and 195 g ha^–1 for the urea and KNO₃ treatments, respectively.     

Molecular insight into the micro-behaviors of CH4 and CO2 in montmorillonite slit-nanopores

Abstract

The Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulation methods were used to investigate the adsorption and diffusion properties of CH₄ and CO₂ in montmorillonite slit-nanopores. It is found that, both CH₄ and CO₂ could adsorb closely onto the pore surface, while different adsorption states occur for CH₄ and CO₂, respectively, in montmorillonite slit-nanopores. Competitive adsorption of CO₂ over CH₄ exists in montmorillonite slit-nanopores, especially at the lower pressures, which is attributed to the different interaction intensity between the CH₄–CO₂ molecules and the pore surface. The diffusion coefficients of CH₄ and CO₂ both decrease with the enhanced pressures, while the CO₂ has a relative weak diffusion coefficient comparing with CH₄. A well displacement of the residual CH₄ by CO₂ in montmorillonite slit-nanopores was investigated, which is found that the displacement efficiency increases with the enhanced bulk pressures. It was determined that, the CO₂ can be captured and reserved in the montmorillonite slit-nanopores during the displacement, and the sequestration amount of CO₂ gets enhanced with the bulk pressure increasing. This study provides micro-behaviours of CH₄ and CO₂ in montmorillonite slit-nanopores, for the purpose to give out useful guidance for enhancing shale gas extraction by injecting CO₂.     

Linking Belowground Carbon Allocation to Anaerobic CH4 and CO2 Production in a Forested Peatland,New York State

Heterotrophic soil microorganisms rely on carbon (C) allocated belowground in plant production, but belowground C allocation (BCA) by plants is a poorly quantified part of ecosystem C cycling, especially, in peat soil. We applied a C balance approach to quantify BCA in a mixed conifer-red maple (Acer rubrum) forest on deep peat soil. Direct measurements of CH₄ and CO₂ fluxes across the soil surface (soil respiration), production of fine and small plant roots, and aboveground litterfall were used to estimate respiration by roots, by mycorrhizae and by free-living soil microorganisms. Measurements occurred in two consecutive years. Soil respiration rates averaged 1.2 bm μmol m^{? 2} s^{? 1} for CO₂ and 0.58 nmol m^{? 2} s^{? 1} for CH₄ (371 to 403 g C m^{? 2} year^{? 1}). Carbon in aboveground litter (144 g C m^{? 2} year^{? 1}) was 84% greater than C in root production (78 g C m^{? 2} year^{? 1}). Complementary in vitro assays located high rates of anaerobic microbial activity, including methanogenesis, in a dense layer of roots overlying the peat soil and in large-sized fragments within the peat matrix. Large-sized fragments were decomposing roots and aboveground leaf and twig litter, indicating that relatively fresh plant production supported most of the anaerobic microbial activity. Respiration by free-living soil microorganisms in deep peat accounted for, at most, 29 to 38 g C m^{? 2} year^{? 1}. These data emphasize the close coupling between plant production, ecosystem-level C cycling and soil microbial ecology, which BCA can help reveal.     

Four years continuous record of CH4-exchange between the atmosphere and untreated and limed soil of a N-saturated spruce and beech forest ecosystem in Germany

In order to gain information about seasonal and interannual variations of CH₄-fluxes at a spruce control site, a limed spruce site and a beech site of the Höglwald Forest, Bavaria, Germany, complete annual cycles of CH₄-exchange between the soil and the atmosphere with 2-hourly resolution were followed for 4 consecutive years. The ranges of CH₄ fluxes observed for the different sites were: +12.4 to –69.4 g CH₄ m^–2 h^–1 (spruce control site), +11.7 to –51.4 g CH₄ m^–2 h^–1 (limed spruce site), and –4.4 to –167.3 g CH₄ m^–2 h^–1 (beech site). Lowest rates of atmospheric CH₄-uptake or even a weak net-emission of CH₄ by the soils were observed during winter/spring times, whereas highest rates of CH₄-uptake were always found in summer/spring. Over the entire observation period of 4 years, mean CH₄-uptake rates were –1.82 kg CH₄-C ha^–1 yr^–1 at the spruce control site, –1.31 kg CH₄-C ha^–1 yr^–1 at the limed spruce site, and –4.84 kg CH₄-C ha^–1 yr^–1 at the beech site. The results obtained in this study demonstrate that in view of the huge interannual variations in CH₄-fluxes of approx. 1 kg CH₄-C ha^–1 yr^–1, multiple year measurements of CH₄-fluxes are necessary to accurately characterize the sink strength of temperate forest for atmospheric CH₄. By comparison of CH₄-fluxes measured at the spruce control site and the limed spruce site, a significant negative effect of forest floor liming on CH₄-uptake could be demonstrated. Compared to the spruce stand, the beech stand showed on average approx. 3 times higher rates of atmospheric CH₄-uptake, most likely due to pronounced differences between both sites with regard to the organic layer structure and bulk density of the mineral soil. Regression analysis between CH₄-fluxes and environmental parameters revealed that at all sites the dominating factors regulating temporal variations of CH₄ fluxes were soil moisture and soil temperature. Field measurements of CH₄ concentrations in the soil profile and laboratory measurements of CH₄-oxidation and CH₄-production activity on soil samples taken from different soil depths showed that the CH₄-flux at the Höglwald Forest sites is the net-result of simultaneous occurring production and consumption of CH₄ within the soil. Highest CH₄-oxidation activity was found in the uppermost centimeters of the mineral soil, whereas highest potential CH₄-production activity was found in the organic layer.     

Hydrophilicity effect on CO2/CH4 separation using carbon nanotube membranes: insights from molecular simulation

Abstract

Molecular simulation methods were applied to study the effect of hydrophilicity on CO₂/CH₄ separation using carbon nanotube (CNT) membranes. CNTs with a diameter of ~1 nm were functionalised by varying amounts of carbonyl groups, in order to achieve various hydrophilicity. The presence of –CO groups inside the CNT allow a significant gain in the diffusion selectivity of CO₂, while in contrast the adsorption selectivity is hardly changed. The corresponding permeation selectivity increases as the hydrophilicity of the CNT-based membrane increases. However, the permeability of CO₂ decreases due to a combination of the intermolecular interactions between the gas and functional groups and the steric effects of the added functional groups. Considering both the permeation selectivity and permeability, it was found that the maximum separation performance is achieved in a certain hydrophilic CNT membrane. Moreover, the separation performance of hydrophilic CNTs for CO₂/CH₄ mixtures breaks the Robeson upper bound.     

Changing land use reduces soil CH4 uptake by altering biomass and activity but not composition of high-affinity methanotrophs

Forest ecosystems assimilate more CO₂ from the atmosphere and store more carbon in woody biomass than most nonforest ecosystems, indicating strong potential for afforestation to serve as a carbon management tool. However, converting grasslands to forests could affect ecosystem–atmosphere exchanges of other greenhouse gases, such as nitrous oxide and methane (CH₄), effects that are rarely considered. Here, we show that afforestation on a well-aerated grassland in Siberia reduces soil CH₄ uptake by a factor of 3 after 35 years of tree growth. The decline in CH₄ oxidation was observed both in the field and in laboratory incubation studies under controlled environmental conditions, suggesting that not only physical but also biological factors are responsible for the observed effect. Using incubation experiments with ¹³CH₄ and tracking ¹³C incorporation into bacterial phospholipid fatty acid (PLFA), we found that, at low CH₄ concentrations, most of the ¹³C was incorporated into only two PLFAs, 18 : 1ω7 and 16 : 0. High CH₄ concentration increased total ¹³C incorporation and the number of PLFA peaks that became labeled, suggesting that the microbial assemblage oxidizing CH₄ shifts with ambient CH₄ concentration. Forests and grasslands exhibited similar labeling profiles for the high-affinity methanotrophs, suggesting that largely the same general groups of methanotrophs were active in both ecosystems. Both PLFA concentration and labeling patterns indicate a threefold decline in the biomass of active methanotrophs due to afforestation, but little change in the methanotroph community. Because the grassland consumed CH₄ at a rate five times higher than forest soils under laboratory conditions, we concluded that not only biomass but also cell-specific activity was higher in grassland than in afforested plots. While the decline in biomass of active methanotrophs can be explained by site preparation (plowing), inorganic N (especially NH₄⁺) could be responsible for the change in cell-specific activity. Overall, the negative effect of afforestation of upland grassland on soil CH₄ uptake can be largely explained by the reduction in biomass and to a lesser extent by reduced cell-specific activity of CH₄-oxidizing bacteria.     

Decomposition of CH4 hydrate: effects of temperature and salt from molecular simulations

We report a molecular simulation study to investigate the decomposition of CH₄ hydrate. The decomposition is revealed to be stepwise from the outer to inner layers. Upon decomposition, the number of 5¹²6² cages drops faster than that of 5¹² cages. CH₄ molecules are released, dissolved in water, then enter gas phase; meanwhile, CH₄ bubbles may form particularly at a high temperature. Based on the variations of potential energy, order parameter, cage number and density profile of CH₄ at different temperatures (300, 330, 345 and 360 K) and NaCl concentrations (0, 0.6 and 1.8 M), the effects of temperature and salt are comprehensively examined. With increasing temperature, the decomposition in pure water is accelerated, whereas two opposite effects are observed in NaCl solution. At 330 K, the decomposition is retarded at a higher NaCl concentration, as attributed to the reduced CH₄ solubility in NaCl solution and the participation of ions in cage formation; at 360 K, however, the decomposition is accelerated when NaCl concentration increases due to bubble formation. This simulation study provides microscopic insights into hydrate decomposition, which might be useful towards the optimisation of operating conditions for CH₄ production from CH₄ hydrate.     

放牧对若尔盖高原湿地CH4排放的影响

湿地是大气甲烷(CH_4)的主要排放源,而有关放牧对湿地CH_4排放的影响特征仍未得到足够的报道。因此,通过静态箱法,研究了放牧对四川省若尔盖高原湿地CH_4排放的影响,CH_4气体通过快速温室气体分析仪测量。结果表明:放牧样地和围栏内样地生长季CH_4排放量为(31.32±19.57)g/m~2和(30.31±23.46)g/m~2,它们之间无差异显著;但是集中放牧期间(7—9月),放牧样地(21.01±12.35)g/m~2较围栏内样地显著增加了CH_4排放量为54.3%。2014年生长季期间通过刈割植物模拟放牧表明两种刈割强度CH_4排放量为(5.01±5.37)g/m~2和(4.69±5.99)g/m~2,较未刈割样地(1.15±1.89)g/m~2增加了335.9%和308.0%,其原因可能是放牧或者刈割减少地表植物生物量,降低植物高度,缩短了CH_4排放的路径距离。该结果可为我国高原湿地保护与管理决策提供基础数据支撑。     

Simulation of separation of C2H6 from CH4 using zeolitic imidazolate frameworks

Separation of important chemical feedstocks, such as C₂H₆ from natural gas, can greatly benefit the petrochemical industry. In this paper, the grand canonical Monte Carlo method has been used to study the adsorption and separation of CH₄ and C₂H₆ in zeolites, isoreticular metal-organic framework-1 (IRMOF-1) and zeolitic imidazolate frameworks (ZIFs) with different topology, including soadlite, gmelinite and RHO topologies. Compared with mordenite zeolite and IRMOF-1, ZIFs and mordenite framework inverted (MFI) zeolite have better separation performance for C₂H₆/CH₄ mixtures at different mole fractions of C₂H₆. From the study of equilibrium snapshots and density distribution profiles, adsorption sites could be grouped as (1) sites with strong interactions with adsorbent and (2) sites with strong interactions with surrounding adsorbates. The gas molecules occupied the first site and then went on to occupy the second site. In CH₄/C₂H₆ mixture adsorption/separation, the adsorption of CH₄ was confined by the existence of C₂H₆. Due to energetic effect, C₂H₆ selectivity was affected by temperature at a low-pressure range, but did not change as much in a high-pressure range because of packing effect in micropore. In binary adsorption, large C₂H₆ molecules favour sites with strong adsorbent interactions. At high pressures, packing effects played an important role and it became easy for small CH₄ molecules to access the sites with strong adsorbate interactions.     

Diversity of active aerobic methanotrophs along depth profiles of arctic and subarctic lake water column and sediments

Methane (CH₄) emitted from high-latitude lakes accounts for 2–6% of the global atmospheric CH₄ budget. Methanotrophs in lake sediments and water columns mitigate the amount of CH₄ that enters the atmosphere, yet their identity and activity in arctic and subarctic lakes are poorly understood. We used stable isotope probing (SIP), quantitative PCR (Q-PCR), pyrosequencing and enrichment cultures to determine the identity and diversity of active aerobic methanotrophs in the water columns and sediments (0–25 cm) from an arctic tundra lake (Lake Qalluuraq) on the north slope of Alaska and a subarctic taiga lake (Lake Killarney) in Alaska''s interior. The water column CH₄ oxidation potential for these shallow (∼2 m deep) lakes was greatest in hypoxic bottom water from the subarctic lake. The type II methanotroph, Methylocystis, was prevalent in enrichment cultures of planktonic methanotrophs from the water columns. In the sediments, type I methanotrophs (Methylobacter, Methylosoma and Methylomonas) at the sediment-water interface (0–1 cm) were most active in assimilating CH₄, whereas the type I methanotroph Methylobacter and/or type II methanotroph Methylocystis contributed substantially to carbon acquisition in the deeper (15–20 cm) sediments. In addition to methanotrophs, an unexpectedly high abundance of methylotrophs also actively utilized CH₄-derived carbon. This study provides new insight into the identity and activity of methanotrophs in the sediments and water from high-latitude lakes.     

张掖湿地甲烷通量动态特征及其影响因子

于2012年7月—2014年6月对地处干旱区的张掖湿地甲烷(CH_4)通量进行观测,分析其CH_4通量的变化特征及其影响因子。结果表明:CH_4通量的日变化趋势总体表现为白天大于夜间;不同季节CH_4通量排放特征差异明显,夏季最大,春秋次之,冬季最小;CH_4通量日总量与空气温度、土壤温度之间指数相关关系显著,其中4 cm处土壤温度与之相关性最强;1—6月摩擦风速(U*)与CH_4通量显著正相关;结合CO_2通量观测数据,研究时段张掖湿地净碳吸收量为495.92 g C m~(-2)a~(-1),为明显碳汇。     

Influence of elevated CO2 and nitrogen nutrition on rice plant growth,soil microbial biomass,dissolved organic carbon and dissolved CH4

Rice (Oryza sativa) was grown in six sunlit, semi-closed growth chambers for two seasons at 350 L L^–1 (ambient) and 650 L L^–1 (elevated) CO₂ and different levels of nitrogen (N) supplement. The objective of this research was to study the influence of CO₂ enrichment and N nutrition on rice plant growth, soil microbial biomass, dissolved organic carbon (DOC) and dissolved CH₄. Elevated CO₂ concentration ([CO₂]) demonstrated a wide range of enhancement to both above- and below-ground plant biomass, in particular to stems and roots (for roots when N was not limiting) in the mid-season (80 days after transplanting) and stems/ears at the final harvest, depending on season and the level of N supplement. Elevated [CO₂] significantly increased microbial biomass carbon in the surface 5 cm soil when N (90 kg ha^–1) was in sufficient supply. Low N supplement (30 kg ha^–1) limited the enhancement of root growth by elevated [CO₂], leading consequently to diminished response of soil microbial biomass carbon to CO₂ enrichment. The concentration of dissolved CH₄ (as well as soil DOC, but to a lesser degree) was observed to be positively related to elevated [CO₂], especially at high rate of N application (120 kg ha^–1) or at 10 cm depth (versus 5 cm depth) in the later half of the growing season (at 80 kg N ha^–1). Root senescence in the late season complicated the assessment of the effect of elevated [CO₂] on root growth and soil organic carbon turnover and thus caution should be taken when interpreting respective high CO₂ results.     

长期施肥对双季稻田甲烷排放和关键功能微生物的影响

研究不同施肥措施对双季稻田甲烷(CH_4)排放特征的影响及其微生物学机理,对合理利用及评价不同施肥模式对水稻生长的影响具有重要意义。以长期施肥定位试验田为平台,采用静态箱-气相色谱法对施用化肥(MF:mineral fertilizer alone)、秸秆还田配施化肥(RF:rice residues plus mineral fertilizer)、30%有机肥配施70%化肥(LOM:30%organic matter plus 70%mineral fertilizer)、60%有机肥配施40%化肥(HOM:60%organic matter plus 40%mineral fertilizer)和无肥(CK:without fertilizer)条件下双季稻田CH_4排放及其微生物学机理进行了分析。结果表明,早稻和晚稻生长期,不同施肥处理稻田CH_4排放通量均显著高于CK,表现为HOMLOMRFMFCK。各处理间CH_4总排放量差异达显著水平,其大小顺序与排放通量趋势一致,以HOM处理为最高,比CK处理增加105.56%,其次是LOM和RF处理,分别比CK处理增加72.97%和54.17%。关键功能土壤微生物测定结果表明,早稻和晚稻各个主要生育时期,各处理稻田土壤产甲烷古菌的数量变化范围为(3.18—81.07)×10~3cfu/g,土壤甲烷氧化细菌的数量变化范围为(24.82—379.72)×10~3cfu/g。稻田土壤产甲烷古菌和甲烷氧化细菌数量大小顺序为HOMLOMRFMFCK,各施肥处理均显著高于CK;HOM、LOM、RF处理显著高于MF、CK处理。双季稻田CH_4排放与稻田土壤产甲烷古菌、甲烷氧化细菌数量变化关系密切。采用有机无机肥配施促进了双季稻田生态系统CH_4的排放和关键功能微生物的数量。     

Effect of urea fertilizer and environmental factors on CH4 emissions from a Louisiana,USA rice field

Methane emissions from a flooded Louisiana, USA, rice field were measured over the first cropgrowing season. Microplots contained the semidwarf Lemont rice cultivar drill seeded into a Crowley silt loam soil (Typic Albaqualfs). Urea fertilizer was applied preflood at rates of 0, 100, 200 and 300 kg N ha^–1. Emissions of CH₄ from the plots to the atmosphere were measured over a 86-d sampling period until harvest. Methane samples were collected in the morning hours (0730–0930) using a closed-chamber technique. Emissions of CH₄ were highly variable over the first cropping season and a significant urea fertilizer effect was observed. Two peak CH₄ emission periods were observed and occurred about 11 d after panicle differentiation and during the ripening stages. Maximum CH₄ emmissions from the 0, 100, 200 and 300 urea-N treatments were 6.0, 8.9, 9.8 and 11.2 kg CH₄ ha^–1 d^–1, respectively. These flux measurements corresponded to approximately 210, 300, 310 and 360 kg CH₄ evolved ha^–1 over the 86-d sampling period for the 4 treatments.     

稻田土壤氧化态有机碳组分变化及其与甲烷排放的关联性

稻田土壤有机碳是甲烷排放的关键底物之一,不同研究者由于采取的有机碳研究方法不同而得出稻田甲烷排放与土壤有机碳关系的结论不一.为明确影响稻田甲烷排放的土壤有机碳组分,设计了稻田施用不同外源有机碳(稻草还田、鸡粪和猪粪)的田间试验,对稻田甲烷排放和土壤有机碳组分的动态变化及其关联性进行监测和分析.结果表明,猪粪处理的甲烷排放与化肥处理无显著差异,而鸡粪和稻草2个处理的甲烷排放分别比化肥增加1.67倍(P＜0.05),2.69倍(P＜0.05);甲烷排放量与土壤易氧化有机碳含量显示相同顺序:稻草＞鸡粪＞猪粪＞化肥;通径分析表明,土壤易氧化有机碳组分1(被33 mmol/L KMnO4氧化的有机碳)与甲烷排放直接相关,其他有机碳组分仅通过组分1间接作用于水稻生育后期甲烷排放,且排放量较低.由此推断,易氧化有机碳组分1是甲烷排放的主要底物,通过有效措施降低肥源中易氧化态有机碳组分1是减排甲烷的关键技术之一.     

免耕施肥对稻田甲烷与氧化亚氮排放及其温室效应的影响

2008年采用静态箱-气相色谱法对鄂东南免耕不施肥(NT₀)、翻耕不施肥(CT₀)、免耕施肥(NTC)和翻耕施肥(CTC) 4种处理下稻田CH₄和N₂O的排放进行测定.结果表明：各处理CH₄排放均呈先升高后降低的季节性规律,而N₂O排放的季节性规律不明显;施肥显著提高了稻田CH₄和N₂O的排放.与翻耕不施肥相比,免耕不施肥显著提高了CH₄的排放量,并显著降低了N₂O的排放量;与翻耕施肥相比,免耕施肥仅略降低了CH₄的排放量和略提高了N₂O的排放量.对稻田CH₄和N₂O两种气体的综合温室效应分析表明,与翻耕不施肥相比,免耕不施肥的综合温室效应提高了25.9%,与翻耕施肥相比,免耕施肥的综合温室效应降低了10.1%.因此,合理的肥料运筹和稻田免耕技术可降低两种气体的综合温室效应.     

Effects of vegetation on the emission of methane from submerged paddy soil

Summary Methane emission rates from rice-vegetated paddy fields followed a seasonal pattern different to that of weed-covered or unvegetated fields. Presence of rice plants stimulated the emission of CH₄ both in the laboratory and in the field. In unvegetated paddy fields CH₄ was emitted almost exclusively by ebullition. By contrast, in rice-vegetated fields more than 90% of the CH₄ emission was due to plant-mediated transport. Rice plants stimulated methanogenesis in the submerged soil, but also enhanced the CH₄ oxidation rates within the rhizosphere so that only 23% of the produced CH₄ was emitted. Gas bubbles in vegetated paddy soils contained lower CH₄ mixing ratios than in unvegetated fiels. Weed plants were also efficient in mediating gas exchnage between submerged soil and atmosphere, but did not stimulate methanogenesis. Weed plants caused a relatively high redox potential in the submerged soil so that 95% of the produced CH₄ was oxidized and did not reach the atmosphere. The emission of CH₄ was stimulated, however, when the cultures were incubated under gas atmospheres containing acetylene or consisting of O₂-free nitrogen.     

湿地甲烷代谢对氮输入响应的复杂性及其机制分析

氮素是影响湿地甲烷代谢过程的重要因素之一。氮输入是否影响湿地甲烷排放,增加全球气候变暖的风险,一直受到科学界的高度关注。目前关于氮输入对湿地甲烷排放影响的几篇meta-analysis文章的主要结论均为氮输入促进湿地甲烷排放,但是多篇研究性论文的结果为氮输入抑制或不影响湿地甲烷排放,由此可见氮输入对湿地甲烷排放的影响十分复杂。湿地甲烷代谢包括湿地甲烷产生、氧化和传输过程以及最终的甲烷排放,综述不同形态氮输入对水稻田、内陆湿地和滨海湿地甲烷排放通量影响的复杂性;分析湿地甲烷产生速率和途径、甲烷好氧氧化和硝酸盐/亚硝酸盐型厌氧甲烷氧化对不同形态氮输入的响应及机制。硝态氮输入对湿地甲烷产生具有抑制作用已成共识,然而其它形态氮输入对湿地土壤甲烷产生的影响具有较大的不确定性,氮输入影响湿地甲烷产生的机制主要包括电子受体-底物竞争机制、离子毒性机制、促进植物生长-碳底物供给增加机制以及pH调控机制等。氮输入对湿地好氧甲烷氧化影响的研究多集中在水稻田和泥炭湿地,影响的结果包括促进、抑制或影响不显著;氮输入促进湿地土壤硝酸盐/亚硝酸盐型厌氧甲烷氧化。着重分析氮输入对湿地甲烷代谢影响不确定性的成因,指出...     

Diversity and activity of methanotrophs in landfill cover soils with and without landfill gas recovery systems

Aerobic CH₄ oxidation plays an important role in mitigating CH₄ release from landfills to the atmosphere. Therefore, in this study, oxidation activity and community of methanotrophs were investigated in a subtropical landfill. Among the three sites investigated, the highest CH₄ concentration was detected in the landfill cover soil of the site (A) without a landfill gas (LFG) recovery system, although the refuse in the site had been deposited for a longer time (∼14–15 years) compared to the other two sites (∼6–11 years) where a LFG recovery system was applied. In April and September, the higher CH₄ flux was detected in site A with 72.4 and 51.7 g m⁻² d⁻¹, respectively, compared to the other sites. The abundance of methanotrophs assessed by quantification of pmoA varied with location and season. A linear relationship was observed between the abundance of methanotrophs and CH₄ concentrations in the landfill cover soils (R = 0.827, P < 0.001). The key factors influencing the methanotrophic diversity in the landfill cover soils were pH, the water content and the CH₄ concentration in the soil, of which pH was the most important factor. Type I methanotrophs, including Methylococcus, Methylosarcina, Methylomicrobium and Methylobacter, and type II methanotrophs (Methylocystis) were all detected in the landfill cover soils, with Methylocystis and Methylosarcina being the dominant genera. Methylocystis was abundant in the slightly acidic landfill cover soil, especially in September, and represented more than 89% of the total terminal-restriction fragment abundance. These findings indicated that the LFG recovery system, as well as physical and chemical parameters, affected the diversity and activity of methanotrophs in landfill cover soils.     

温带针阔混交林土壤碳氮气体通量的主控因子与耦合关系

中高纬度森林地区由于气候条件变化剧烈,土壤温室气体排放量的估算存在很大的不确定性,并且不同碳氮气体通量的主控因子与耦合关系尚不明确。以长白山温带针阔混交林为研究对象,采用静态箱-气相色谱法连续4a(2005—2009年)测定土壤二氧化碳(CO2)、甲烷(CH4)和氧化亚氮(N2O)净交换通量以及温度、水分等相关环境因子。研究结果表明:温带针阔混交林土壤整体上表现为CO2和N2O的排放源和CH4的吸收汇。土壤CH4、CO2和N2O通量的年均值分别为-1.3 kg CH4hm-2a-1、15102.2 kg CO2hm-2a-1和6.13 kg N2O hm-2a-1。土壤CO2通量呈现明显的季节性规律,主要受土壤温度的影响,水分次之;土壤CH4通量的季节变化不明显,与土壤水分显著正相关;土壤N2O通量季节变化与土壤CO2通量相似,与土壤水分、温度显著正相关。土壤CO2通量和CH4通量不存在任何类型的耦合关系,与N2O通量也不存在耦合关系;土壤CH4和N2O通量之间表现为消长型耦合关系。这项研究显示温带针阔混交林土壤碳氮气体通量主要受环境因子驱动,不同气体通量产生与消耗之间存在复杂的耦合关系,下一步研究需要深入探讨环境变化对其耦合关系的影响以及内在的生物驱动机制。