甲烷氧化细菌Methylosinus trichosporium 3011甲醇累积条件的研究

本文考察了甲烷氧化细菌Methylosi nus trichosporium 3011的生理特性及反应条件对甲烷单加氧酶和甲醇累积的影响。M.3011菌株在4℃保存30～40天内,菌株的细胞生长量和甲烷单加氧酶活性均不受影响。在生长对数期收获细胞,其甲烷单加氧酶活力最高可达125nmol甲醇/mg(细胞干重)·min。在M.3011菌株的生长对数期后期收集细胞,将反应菌悬液浓度控制在0.15—0.3mg(细胞干重/ml,pH为6.7,反应温度为35℃,甲醇累积量可达3.1μmol甲醇/mg(细胞干重)·h。反应液的磷酸缓冲液的最适浓度为60mmol/L。     

三硝酸丙三酯对厌氧真菌和甲烷菌代谢产物、纤维水解酶活性及菌群丰度的影响

【背景】近年来硝酸酯化合物抑制瘤胃甲烷生成的能力受到广泛关注,但鲜有研究关注其对瘤胃内主要纤维降解菌——厌氧真菌的影响。【目的】研究三硝酸丙三酯(Nitroglycerin,NG)对厌氧真菌和甲烷菌活性和代谢的影响。【方法】利用厌氧真菌(Piromyces sp.F1)纯培养及与甲烷菌共培养(Piromyces sp.F1+Methanobrevibacter sp.),比较不同剂量NG(0.0、6.6、13.2和19.8μmol/L)对厌氧真菌和甲烷菌的代谢终产物、主要纤维水解酶活性及菌群丰度的影响。【结果】厌氧真菌共培养组中,6.6μmol/L NG完全抑制了甲烷的生成,积累了氢气和甲酸(P0.05),降低了乙酸浓度以及木聚糖酶和羧甲基纤维素酶活性(P0.05),但未显著影响厌氧真菌和甲烷菌的丰度(P0.05)。厌氧真菌纯培养组中,6.6μmol/L NG显著降低了甲酸、乙酸、乙醇、木聚糖酶和羧甲基纤维素酶活性(P0.05),但总产气量和氢气产量没有显著差异(P0.05)。在2个培养体系中,随着剂量的升高,NG对厌氧真菌和甲烷菌的抑制增强。【结论】NG能够抑制甲烷菌的活性,但对厌氧真菌也有抑制作用。     

典型草地土壤好氧甲烷氧化的微生物生态过程

【目的】针对我国甘肃三个典型生态区草地土壤(玛曲MQ、临泽LZ和环县HX),研究其甲烷氧化潜力、甲烷氧化菌(methane-oxidizingbacteria,MOB)丰度及可能存在的群落分异规律。【方法】通过原位分析、室内高浓度甲烷模拟培养三种典型土壤及实时荧光定量、高通量测序的方法研究甲烷氧化菌标靶基因pmoA序列的组成及其丰度变化规律。【结果】三种典型草地土壤的原位甲烷氧化菌的丰度存在显著差异,表现为MQ>HX>LZ,其数量范围为为0.18–6.86×10^7g/d.w.s.;甲烷氧化潜力也表现出类似规律,其通量为109–169mg/(m^2·h);甲烷氧化潜力与原位土壤中甲烷氧化菌丰度有正相关。三种草地土壤甲烷氧化菌存在明显的空间异质性,采用高通量测序的方法,发现三种草地原位土壤中的优势类群为USCγ(Upland Soil Cluster gamma,USCγ);然而,室内高浓度甲烷氧化过程中,传统的甲烷氧化菌均发生明显增加,MQ土壤中TypeⅡ的Methylocystis为优势类群,而LZ和HX土壤的优势类群均为TypeⅠ型Methylosarcina。【结论】这些研究结果表明,我国甘肃典型草地土壤中也存在难培养的大气甲烷氧化菌和经典的可培养甲烷氧化菌,这些微生物极可能氧化极低浓度的大气甲烷,也可能利用闭蓄于土壤中的高浓度甲烷生长。未来应采用先进技术原位观测大气甲烷氧化过程并分离相应微生物类群,研究草地土壤甲烷氧化菌地理分异规律及其环境驱动机制。     

稻鱼共生系统的土壤产甲烷和甲烷氧化微生物群落

稻鱼共生对稻田甲烷(CH₄)排放产生明显影响，但稻鱼共生是否影响与CH₄排放相关的产甲烷菌和甲烷氧化菌仍有待阐明。本研究以全球重要农业文化遗产——青田稻鱼系统为例，通过田间试验，比较研究了水稻单作系统(RM)、无饲料投放的稻鱼共生系统(RFN)和有饲料投放的稻鱼共生系统(RFF)水稻和田鱼的产量、土壤碳氮磷含量以及产甲烷和甲烷氧化微生物的特征。结果表明，RFF的水稻产量和土壤碳氮增量均显著高于RM。荧光定量PCR分析表明，稻鱼共生(RFN和RFF)的产甲烷菌和甲烷氧化菌丰度显著高于RM,且RFF的产甲烷菌丰度显著高于RFN。Illumina Miseq测序分析表明，稻鱼共生显著影响产甲烷菌群落结构，但对甲烷氧化菌群落结构的影响不显著；对于不同代谢类型的产甲烷菌，稻鱼共生(RFN和RFF)氢营养型产甲烷菌的丰度显著高于RM,且RFF的乙酸营养型产甲烷菌丰度显著高于RFN;对于不同代谢类型的甲烷氧化菌，RFN和RFF对类型Ⅰ的甲烷氧化菌丰度影响均不显著；RFF中类型Ⅱ的甲烷氧化菌丰度显著高于RM和RFN。可见，稻鱼共生可明显影响产甲烷菌和甲烷氧化...     

甲烷氧化菌及甲烷单加氧酶的研究进展

甲烷氧化菌是以甲烷作为唯一碳源和能源进行同化和异化代谢的微生物,其关键酶之一是甲烷单加氧酶(MMOs),可以在氧气的作用下催化甲烷等低碳烷烃或烯烃羟基化或环氧化,甲烷氧化菌在自然界碳循环和工业生物技术中具有重要的应用价值.因此,近20年来对于甲烷氧化菌和MMOs的研究一直倍受生物学家的关注.以下从现代生物技术的角度,对近年来国内外在甲烷氧化菌的分类与分布,MMOs的结构与功能、甲烷氧化菌与MMOs的基因工程等方面取得的研究成果进行了总结,全面综述了甲烷氧化菌及MMOs的应用基础研究现状,并对其今后的研究和应用方向提出了展望.     

不同抑制剂对乙酸降解产甲烷及产甲烷菌群结构的影响

摘要:【目的】研究不同温度条件下的石油烃降解产甲烷菌系中是否存在乙酸互营氧化产甲烷代谢途径。【方法】以3个不同温度条件的正十六烷烃降解产甲烷菌系Y15(15℃)、M82(35℃)和SK(55℃)作为接种物,通过乙酸喂养实验、并添加乙酸营养型产甲烷古菌的选择性抑制剂NH4Cl和CH3F,结合末端限制性片段长度多态性(terminal restriction fragment length polymorphism,T-RFLP)和克隆文库技术,分析乙酸产甲烷潜力及产甲烷古菌群落的演替趋势,推测产甲烷代谢途径的变化趋势。【结果】无论是否添加NH4Cl和CH3 F,这3个菌系都可以利用乙酸生长并产生甲烷,但是添加NH4Cl和CH3 F后产甲烷延滞期增加,最大比甲烷增长速率降低;只添加乙酸后,3个不同温度的菌系的古菌群落主要由乙酸营养型产甲烷古菌甲烷鬃毛菌属(Methanosaeta)组成,其丰度分别为92.8±1.4%、97.3±2.4%和82.8±9.0%;当添加选择性抑制剂NH4Cl,3 个菌系中的Methanosaeta的丰度分别变为98.5±0.7%、87.4±4.8%和6.1±8.6%,中温菌系M82中氢营养型产甲烷古菌甲烷袋装菌属(Methanoculleus)的相对丰度增加到12. 6±4.0%,高温菌系SK中另一类氢营养型产甲烷古菌甲烷热杆菌属(Methanothermobacter)增至84.3±1.5%;当添加选择性抑制剂CH3 F,Methanosaeta丰度分别降至77.1 ± 14.5%,86.4±6.1%和35.8±7.8%,低温菌系Y15中的甲烷八叠球菌属(Methanosarcina)增高(15.7±21%),这类产甲烷古菌具有多种产甲烷代谢途径,M82中Methanoculleus丰度上升到13.6±13.1%,SK中Methanothermobacter丰度增大到48.5±11.2%。【结论】在低温条件下,菌系Y15可能主要通过乙酸裂解完成产甲烷代谢,在中高温条件下,菌系M82和SK中可能存在乙酸互营氧化产甲烷代谢途径,并且甲烷的产生分别通过不同种群的氢营养型产甲烷古菌来完成。     

论文“甲烷氧化菌20Z利用Embden-Meyerhof-Parnas途径高效同化甲烷”的撤稿声明

<正>崔金玉等发表在《生物工程学报》的论文:甲烷氧化菌20Z利用Embden-Meyerhof-Parnas途径高效同化甲烷(2014,30(1):43-54),因作者提出该论文中所述部分研究方法学应用于该细菌尚有缺陷,可能导致相关的研究结果 (详见作者来信)存在较大偏差,考虑到科学研究的严谨性和真实性,为了不对该领域同行和其他读者造成误导,本刊尊重作者请求撤销该论文,特此声明。编委会同时对作者实事求是,有错即纠的科学态度表示赞赏和肯定。     

土壤大气甲烷氧化菌研究进展

土壤微生物催化是大气中痕量甲烷(约1.8ppmv)氧化的唯一生物途径。目前的研究表明好氧土壤中存在专性和选择性大气甲烷氧化菌2种类型:前者(USCα和USCγ)广泛分布于各种好氧旱地土壤,其甲烷氧化酶对低浓度甲烷亲和力极高,属真正的寡营养型,但至今尚未获得该种类的纯培养菌株。后者属于传统甲烷氧化菌Methylocystis/Methylosinus属,广泛分布于各种周期性排放高浓度甲烷的土壤环境中。该属大部分菌株含有亲和力不同的2套甲烷单加氧酶系统,其中的高亲和力甲烷单加氧酶使这些菌株可以在相当长的时间内(3个月)保持大气浓度甲烷氧化活性,但其生长和繁殖还需依赖于土壤内部阶段性产生的高浓度甲烷。本文详细阐述了2类大气甲烷氧化菌的发现历程及其可能的生存策略,最后系统梳理了几种关键的环境因子(土壤温度及湿度、土壤pH、植被、土地利用及氮输入)对大气甲烷氧化菌群落结构和甲烷氧化活性的影响,提出并展望了土壤大气甲烷氧化菌研究的重要方向。     

共存甲烷短杆菌Methanobrevibacter thaueri F1提高梨囊鞭菌Piromyces sp. F1对硝呋烯腙的耐受性

【背景】硝呋烯腙能够抑制厌氧真菌。共存甲烷菌可以促进厌氧真菌的生长以及对木质纤维素的降解,然而关于共存甲烷菌对厌氧真菌抗逆性影响的研究较少。【目的】旨在研究甲烷菌共存对厌氧真菌耐受硝呋烯腙的影响。【方法】采用体外批次培养,以稻草为底物,添加不同浓度的硝呋烯腙(0、5、10、25 mg/L),分别接种厌氧真菌纯培养和厌氧真菌与甲烷菌共培养悬浮液,于39°C静置培养96 h。测定不同时间点的产气量和甲烷产量,结束后测定p H、干物质降解率(DMD)、中性洗涤纤维消失率(NDFD)、半纤维素消失率(ADSD)、酸性洗涤纤维消失率(ADFD)以及上清液中甲酸、乳酸和乙酸的浓度。【结果】添加5、10和25 mg/L硝呋烯腙皆显著降低了厌氧真菌纯培养的发酵活性(P0.05);添加5 mg/L硝呋烯腙没有显著降低厌氧真菌与甲烷菌共培养的发酵活性(P0.05),添加10和25 mg/L硝呋烯腙则显著降低了共培养发酵活性(P0.05);比较5、10 mg/L硝呋烯腙对纯培养和共培养发酵活性影响的结果表明,共培养发酵活性显著高于纯培养发酵活性(P0.05)。【结论】硝呋烯腙对厌氧真菌纯培养和厌氧真菌与甲烷菌共培养的抑制作用都存在剂量效应,在一定添加浓度范围内(25 mg/L),甲烷菌共存可以显著提高厌氧真菌对硝呋烯腙的耐受性。     

大气CO2浓度缓增对稻田硝酸盐型甲烷厌氧氧化过程的影响

硝酸盐型甲烷厌氧氧化(AOM)是控制稻田甲烷排放的一种新途径,大气CO₂浓度升高会对稻田甲烷排放产生重要影响,但有关其对硝酸盐型AOM过程的影响知之甚少。本研究依托开顶式气室组成的CO₂浓度自动调控平台,采用¹³CH₄稳定性同位素示踪技术,从甲烷氧化活性、相关功能微生物Candidatus Methanoperedens nitroreducens (M. nitroreducens)-like古菌丰度与群落组成等方面,系统研究了稻田土壤中硝酸盐型AOM过程对大气CO₂浓度缓增的响应。试验设置背景CO₂浓度和CO₂浓度缓增处理(背景CO₂浓度基础上每年增加40 μL·L^-1,直至增幅达160 μL·L^-1)。结果表明: 稻田土壤硝酸盐型AOM速率为0.7～11.3 nmol CO₂·g^-1·d^-1;定量PCR结果显示,M. nitroreducens-like古菌mcrA基因丰度为2.2×10⁶～8.5×10⁶ copies·g^-1。与对照相比,CO₂浓度缓增处理使土壤中硝酸盐型AOM速率和M. nitroreducens-like古菌mcrA基因丰度均有一定幅度提高,特别是在5～10 cm深度下两者均显著提高。CO₂浓度缓增处理未显著改变M. nitroreducens-like古菌群落结构,但使其多样性显著降低。相关性分析表明,土壤有机碳含量可能是影响硝酸盐型AOM过程的重要因子。综上,大气CO₂浓度缓增在一定程度上促进了硝酸盐型AOM反应,暗示在未来气候变化背景下其在控制稻田甲烷排放中具有积极作用。     

Processes involved in formation and emission of methane in rice paddies

The seasonal change of the rates of production and emission of methane were determined under in-situ conditions in an Italian rice paddy in 1985 and 1986. The contribution to total emission of CH₄ of plant-mediated transport, ebullition, and diffusion through the flooding water was quantified by cutting the plants and by trapping emerging gas bubbles with funnels. Both production and emission of CH₄ increased during the season and reached a maximum in August. However, the numbers of methanogenic bacteria did not change. As the rice plants grew and the contribution of plant-mediated CH₄ emission increased, the percentage of the produced CH₄ which was reoxidized and thus, was not emitted, also increased. At its maximum, about 300 ml CH₄ were produced per m² per hour. However, only about 6% were emitted and this was by about 96% via plant-mediated transport. Radiotracer experiments showed that CH, was produced from H₂/CO₂. (30–50%) and from acetate. The pool concentration of acetate was in the range of 6–10 mM. The turnover time of acetate was 12–16 h. Part of the acetate pool appeared to be not available for production of CH₄ or CO₂     

Methane emissions from rice microcosms: The balance of production, accumulation and oxidation

In rice microcosms (Oryza sativa, var. Roma, type japonica),CH₄ emission, CH₄ production, CH₄oxidation and CH₄ accumulation were measured over an entirevegetation period. Diffusive CH₄ emission was measured inclosed chambers, CH₄ production was measured in soil samples,CH₄ oxidation was determined from the difference between oxicand anoxic emissions, and CH₄ accumulation was measured byanalysis of porewater and gas bubbles. The sum of diffusiveCH₄ emission, CH₄ oxidation, andCH₄ accumulation was only 60% of the cumulativeCH₄ production. The two values diverged during the first 50days (vegetative phase) and then again during the last 50 days (latereproductive phase and senescence) of the 150 day vegetation period. Duringthe period of day 50–100 (early reproductive phase/flowering), theprocesses were balanced. Most likely, gas bubbles and diffusion limitationare responsible for the divergence in the early and late phases. The effectof rice on CH₄ production rates and CH₄concentrations was studied by measuring these processes also in unplantedmicrocosms. Presence of rice plants lowered the CH₄concentrations, but had no net effect on the CH₄ productionrates.     

盐分对湿地甲烷排放影响的研究进展

当前在全球气候变化和人类活动双重作用下,湿地正在或者将要面临着显著的盐分变化形势,尤其是内陆和滨海咸化湿地。湿地是大气甲烷的重要排放源。甲烷排放是甲烷产生、氧化和传输过程综合作用的结果。盐分变化将影响湿地水-土环境,降低植物群落初级生产力和有机物积累速率,改变微生物主导的有机物矿化速率和途径等,进而改变湿地生态系统的结构和功能,影响湿地甲烷产生、氧化、传输和排放系列过程。本文综述了盐分(浓度与组成)对湿地甲烷产生与排放的影响结果,从底物供给、微生物(产甲烷菌和甲烷氧化菌等)数量、活性与群落组成、酶活性、植物、电子受体、p H和氧化还原电位等几个关键方面分析了盐分影响湿地甲烷排放过程的内在机制。在此基础上提出了今后需重点关注的5个方面:1)加强盐分浓度与组成对湿地甲烷产生、氧化、传输与排放影响的系统性、框架性研究;2)深入探讨盐分背景、变化幅度与速率的耦合如何影响湿地甲烷系列过程;3)不同离子组成及其交互效应如何影响湿地甲烷动态过程;4)结合生物学、基因组学及同位素技术等,加强湿地产甲烷菌与甲烷氧化菌与盐分的关系及其响应研究;5)湿地甲烷对盐分变化响应的时空分异规律。     

Bacterial Processes of the Methane Cycle in Bottom Sediments of Lake Baikal

The activity of methanogenic and methanotrophic bacteria was evaluated in bottom sediments of Lake Baikal. Methane concentration in Baikal bottom sediments varied from 0.0053 to 81.7 ml/dm³. Bacterial methane was produced at rates of 0.0004–534.7 l CH₄/(dm³ day) and oxidized at rates of 0.005–1180 l CH₄/(dm³ day). Peak methane production and oxidation were observed in Frolikha Bay near a methane vent. Methane was emitted into water at rates of 49.2–4340 l CH₄/(m² day). Rates of bacterial methane oxidation in near-bottom water layers ranged from 0.002 to 1.78 l/(l day). Methanogens and methanotrophs were found to play an important role in the carbon cycle through all layers of sediments, particularly in the areas of methane vent and gas-hydrate occurrence.     

The geochemistry of methane in Lake Fryxell,an amictic,permanently ice-covered,antarctic lake

The abundance and distribution of dissolved CH₄ were determined from 1987–1990 in Lake Fryxell, Antarctica, an amictic, permanently ice-covered lake in which solute movement is controlled by diffusion. CH₄ concentrations were < 1 υM in the upper oxic waters, but increased below the oxycline to 936 μM at 18 m. Sediment CH₄ was 1100 μmol (1 sed)⁻¹ in the 0–5 cm zone. Upward flux from the sediment was the source of the CH₄, NH₄ ⁺, and DOC in the water column; CH₄ was 27% of the DOC+CH₄ carbon at 18 m. Incubations with surficial sediments indicated that H¹⁴CO₃ ⁻ reduction was 0.4 μmol (1 sed)⁻¹ day⁻¹ or 4× the rate of acetate fermentation to CH₄. There was no measurable CH₄ production in the water column. However, depth profiles of CH₄, NH₄, and DIC normalized to bottom water concentrations demonstrated that a significant CH₄ sink was evident in the anoxic, sulfate-containing zone of the water column (10–18 m). The δ¹³CH₄ in this zone decreased from −72 % at 18 m to −76% at 12 m, indicating that the consumption mechanism did not result in an isotopic enrichment of ¹³CH₄. In contrast, δ¹³CH₄ increased to −55 % at 9 m due to aerobic oxidation, though this was a minor aspect of the CH₄ cycle. The water column CH₄ profile was modeled by coupling diffusive flux with a first order consumption term; the best-fit rate constant for anaerobic CH₄ consumption was 0.012 yr⁻¹. On a total carbon basis, CH₄ consumption in the anoxic water column exerted a major effect on the flux of carbonaceous material from the underlying sediments and serves to exemplify the importance of CH₄ to carbon cycling in Lake Fryxell.     

甲烷单加氧酶的研究进展

甲烷氧化细菌在转化甲烷制造新型燃料、单细胞蛋白和新功能酶生产、污水处理等方面有着潜在的应用前景,因此,甲烷单加氧酶作为其代谢过程中重要的酶系也受到人们的广泛关注。我们简要综述了近年来对甲烷单加氧酶的性质、结构、催化机理等方面的研究,特别是对颗粒性甲皖单加氧酶的相关性质进行了详细的阐述。     

Oxidation of methane in boreal forest soils: a comparison of seven measures

Methane oxidation rates were measured in boreal forest soils using seven techniques that provide a range of information on soil CH₄ oxidation. These include: (a) short-term static chamber experiments with a free-air (1.7 ppm CH₄) headspace, (b) estimating CH₄ oxidation rates from soil CH₄ distributions and (c)²²²Rn-calibrated flux measurements, (d) day-long static chamber experiments with free-air and amended (+20 to 2000 PPM CH₄) headspaces, (e) jar experiments on soil core sections using free-air and (f) amended (+500 ppm CH₄) headspaces, and (g) jar experiments on core sections involving tracer additions of¹⁴CH₄. Short-term unamended chamber measurements,²²²Rn-calibrated flux measurements, and soil CH₄ distributions show independently that the soils are capable of oxidizing atmospheric CH₄ at rates ranging to < 2 mg m^–2 d^–1. Jar experiments with free-air headspaces and soil CH₄ profiles show that CH₄ oxidation occurs to a soil depth of 60 cm and is maximum in the 10 to 20 cm zone. Jar experiments and chamber measurements with free-air headspaces show that CH₄ oxidation occurs at low (< 0.9 ppm) thresholds. The¹⁴CH₄-amended jar experiments show the distribution of end products of CH₄ oxidation; 60% is transformed to CO₂ and the remainder is incorporated in biomass. Chamber and jar experiments under amended atmospheres show that these soils have a high capacity for CH₄ oxidation and indicate potential CH₄ oxidation rates as high as 867 mg m^–2 d^–1. Methane oxidation in moist soils modulates CH₄ emission and can serve as a negative feedback on atmospheric CH₄ increases.     

Methane consumption in two temperate forest soils

Forest soils are thought to be an important sink for atmospheric methane. To evaluate methane consumption,¹⁴C-labeled methane was added to the headspace of intact soil cores collected from a mixed mesophytic forest and from a red spruce forest located in the central Appalachian Mountains. Both soils consumed the added methane at initially high rates that decreased as the methane mixing ratio of the air decreased. The mixed mesophytic forest soil consumed an average of 2 mg CH₄ m^–2 d^–1 versus 1 mg CH, m^–2 d^–1 for the spruce forest soil. The addition of acetylene to the headspace completely suppressed methane consumption by the soils, suggesting that an aerobic methane-consuming microorganism mediated the process. At both forest sites, methane mixing ratios in soil air spaces were greater than that in the air overlying the soil surface, indicating that these soils had the ability to produce methane. Models of methane emission from forest soils to the atmosphere must represent methane flux as the balance between production and consumption of methane, which are controlled by very different factors     

Soil environmental variables affecting the flux of methane from a range of forest, moorland and agricultural soils

Measurements of the net methane exchange over a range of forest, moorland, and agricultural soils in Scotland were made during the period April to June 1994 and 1995. Fluxes of CH₄ ranged from oxidation –12.3 to an emission of 6.8 ng m^–2 s^–1. The balance between CH₄ oxidation and emission depended on the physical conditions of the soil, primarily soil moisture. The largest oxidation rates were found in the mineral forest soils, and CH₄ emission was observed in several peat soils. The smallest oxidation rate was observed in an agricultural soil. The relationship between CH₄ flux and soil moisture observed in peats (Flux_{CH 4} = 0.023 × %H₂O (dry weight) – 7.44, p > 0.05) was such that CH₄ oxidation was observed at soil moistures less than 325%( ± 80%). CH₄ emission was found at soil moistures exceeding this value. A large range of CH₄ oxidation rates were observed over a small soil moisture range in the mineral soils. CH₄ oxidation in mineral soils was negatively correlated with soil bulk density (Flux_{CH 4} = –37.35 × bulk density (g cm^–3) + 48.83, p > 0.05). Increased nitrogen loading of the soil due to N fixation, atmospheric deposition of N, and fertilisation, were consistently associated with decreases in the soil sink for CH₄, typically in the range 50 to 80%, on a range of soil types and land uses.     

CH4 emission from a hollow-ridge complex in a raised bog: The role of CH4 production and oxidation

The aim of this study was to correlate magnitude andcontrols of CH₄ fluxes with the microtopographyand the vegetation in a hollow-ridge complex of araised bog. High CH₄ emission rates were measuredfrom hollows and mud-bottom hollows, while hummocksconsumed atmospheric CH₄ at a low rate. Thehighest emissions were measured from plots with Eriophorum vaginatum and Scheuchzeriapalustris. CH₄ emission ceased after Scheuchzeria had been clipped below the water table,indicating the importance of this aerenchymatic plantas a conduit for CH₄.Peat in the upper catotelm of hollows was younger andless decomposed than in hummocks. Potential CH₄production in vitro was higher and themethanogenic association was better adapted to highertemperatures in hollow than in hummock peat. Highertemperatures in hollows resulted in a strongerCH₄ source in hollows than in hummocks. Negativefluxes from hummocks indicated that even in wetlandsmethanotrophic bacteria exist that are able to oxidizeCH₄ at atmospheric mixing ratios, and thatoxidation controls CH₄ emission completely. TheCH₄ mixing ratio was low in the acrotelm, but itincreased within the catotelm. Comparing fluxesmeasured in static chambers with fluxes calculatedfrom the porewater CH₄ profiles it was deducedthat the zone of methane oxidation was located closeto the water table.In hollows, CH₄ production at in situtemperature was far higher than emission into theatmosphere, corresponding to an oxidation rate ofnearly 99%. The CH₄ flux between the catotelmand the acrotelm of hollows was also higher than theemission, indicating the importance of CH₄oxidation in the aerobic acrotelm, too. CH₄microprofiles showed that CH₄ oxidation inmud-bottom hollows was confined to the topmost 2 mm,and that in Sphagnum-covered hollows CH₄oxidation occurred at the lower edge of green Sphagnum-parts.