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1.
Methane production and methane consumption: a review of processes underlying wetland methane fluxes 总被引:35,自引:1,他引:34
Reinoud Segers 《Biogeochemistry》1998,41(1):23-51
Potential rates of both methane production and methane consumptionvary over three orders of magnitude and their distribution is skew.These rates are weakly correlated with ecosystem type, incubationtemperature, in situ aeration, latitude, depth and distanceto oxic/anoxic interface. Anaerobic carbon mineralisation is amajor control of methane production. The large range in anaerobicCH4:CO2 production rates indicate that a largepart of the anaerobically mineralised carbon is used for reduction ofelectron acceptors, and, hence, is not available for methanogenesis.Consequently, cycling of electron acceptors needs to be studied tounderstand methane production. Methane and oxygen half saturationconstants for methane oxidation vary about one order of magnitude.Potential methane oxidation seems to be correlated withmethanotrophic biomass. Therefore, variation in potential methaneoxidation could be related to site characteristics with a model ofmethanotrophic biomass. 相似文献
2.
Rodrigo Gonzalez-Valencia Armando Sepulveda-Jauregui Karla Martinez-Cruz Jorge Hoyos-Santillan Luc Dendooven Frederic Thalasso 《Hydrobiologia》2014,721(1):9-22
The literature concerning methane (CH4) emissions from temperate and boreal lakes is extensive, but emissions from tropical and subtropical lakes have been less documented. In particular, methane emissions from Mexican lakes, which are often polluted by anthropogenic carbon and nutrient inputs, have not been reported previously. In this work, methane emissions from six Mexican lakes were measured, covering a broad range of organic inputs, trophic states, and climatic conditions. Methane emissions ranged from 5 to 5,000 mg CH4 m?2 day?1. Water samples from several depths in each lake were analyzed for correlation between water quality indicators and methane emissions. Trophic state and water quality indexes were most strongly correlated with methane fluxes. The global methane flux from Mexican freshwater lakes was estimated to be approximately 1.3 Tg CH4 year?1, which is about 20% of methane and 4.4% of total national greenhouse gas emissions. Data for untreated wastewater releases to the environment gave an emission factor of 0.19 kg CH4 kg?1 of Biochemical Oxygen Demand, which is superior to that previously estimated by the IPCC for lake discharges. Thus, the large volume of untreated wastewater in Mexico implies higher methane emission than previously estimated. 相似文献
3.
内陆湿地与水体甲烷厌氧氧化功能微生物研究进展 总被引:2,自引:0,他引:2
内陆湿地与水体(如湖泊、河流、水库等)是温室气体甲烷的重要排放源。微生物介导的甲烷厌氧氧化(anaerobic oxidation of methane,AOM)反应在控制内陆湿地与水体甲烷排放中起着不可忽视的作用,对缓解全球温室效应具有重要意义。内陆湿地与水体易形成缺氧环境,且电子受体的种类和数量繁多,是发生AOM反应的理想生境。近年来,不断有研究表明,内陆湿地与水体中存在多种电子受体(NO2-、NO3-、SO42-、Fe (III)等)驱动的AOM途径。NC10门细菌和甲烷厌氧氧化古菌(anaerobic methanotrophic archaea,ANME)的一新分支ANME-2d主导了湿地和水体环境中的AOM反应,其中ANME-2d具有根据环境条件选择不同电子受体的潜力。研究系统综述了内陆湿地与水体中不同电子受体驱动的AOM途径及其参与的主要功能微生物类群;分析了AOM反应在控制温室气体甲烷排放中的作用及其环境影响因素;总结了相关功能微生物的分子生物学检测方法及甲烷厌氧氧化活性测定的同位素示踪技术。最后,对未来相关研究方向进行了展望。 相似文献
4.
An attempt was made to calculate growth yields of microorganisms on methanol and methane on the basis of known biochemical pathways of C1 metabolism. Since 3-phosphoglycerate is a key intermediate in the assimilation pathways of C1 compounds, the calculations were based on the assumption that the synthesis of cell material from C1 substrates can be regarded as a two step process. When YATP on 3-phosphoglycerate was taken as 10.5, a maximal cell yield of organisms of the composition C4H8O2N on methanol was found to be 0.73 g cells/g substrate. For growth on methane a value of 0.91 g cells/g substrate was calculated when a mixed function oxidase was implicated in methane oxidation. These yields were calculated on the basis of the ribulose phosphate pathway of formaldehyde fixation as the major pathway of C1 assimilation. Yields calculated on the basis of the serine pathway were on an average 20% lower. The calculations disclosed that for growth on methane, at least for Methylococcus capsulatus, a reversed electron transport system is required when methane is oxidized by a mixed function oxidase. The theoretical cell yields on methanol and methane have been compared with experimentally obtained yields and the validity of the estimations of growth yields on the basis of the present calculations is discussed. 相似文献
5.
Molecular dynamics simulation was performed to analyse the phenomena of replacement of methane hydrate with carbon dioxide (CO2) at 270 K and 5.0 MPa for 5300 ps. The methane hydrate phase was constructed with 16 unit cells of hydrate. Every cage in the hydrate was occupied by one methane molecule. The methane hydrate phase was sandwiched between two CO2 phases. During the simulation the hydrate partially melted and liquid water phase appeared, and CO2 dissolved in the liquid water phase. The replacements were observed three times at the hydrate–liquid water interface during the simulation. In the first case, the replacement occurred at a S-cage without changing the structure. In the second case, an M-cage of methane hydrate partially collapsed, and methane and CO2 molecules exchanged. After the exchange, the cage occupied by CO2 remained in the M-cage structure. In the third case, a S-cage of methane hydrate partially collapsed, and methane and CO2 molecules exchanged. After the exchange, the cage occupied by CO2 changed to an M-cage-like structure. 相似文献
6.
R. Liu D. Hailemariam T. Yang F. Miglior F. Schenkel Z. Wang P. Stothard S. Zhang G. Plastow 《Animal : an international journal of animal bioscience》2022,16(3):100469
Methane emission is not included in the current breeding goals for dairy cattle mainly due to the expense and difficulty in obtaining sufficient data to generate accurate estimates of the relevant traits. While several models have been developed to predict methane emission from milk spectra using reference methane data obtained by the respiration chamber, SF6 and sniffer methods, the prediction of methane emission from milk mid-infrared (MIR) spectra using reference methane data collected by the GreenFeed system has not yet been explored. Methane emission was monitored for 151 cows using the GreenFeed system. Prediction models were developed for daily and average (for the trial period of 12 or 14 days) methane production (g/d), yield (g/kg DM intake (DMI)) and intensity (g/kg of fat- and protein-corrected milk) using partial least squares regression. The predictions were evaluated in 100 repeated validation cycles, where animals were randomly partitioned into training (80%) and testing (20%) populations for each cycle. The best performing model was observed for average methane intensity using MIR, parity and DMI with validation coefficient of determination (R2val) and RMSE of prediction of 0.66 and 4.7 g/kg of fat- and protein-corrected milk, respectively. The accuracy of the best models for average methane production and average methane yield were poor (R2val = 0.28 and 0.12, respectively). A lower accuracy of prediction was observed for methane intensity and production (R2val = 0.42 and 0.17) when daily records were used while prediction for methane yield was comparable to that for average methane yield (R2val = 0.16). Our results suggest the potential to predict methane intensity with moderate accuracy. In this case, prediction models for average methane values were generally better than for daily measures when using the GreenFeed system to obtain reference methane emission measurements. 相似文献
7.
Susan Waldron Irene A. Watson‐Craik Allan J. Hall Anthony E. Fallick 《Geomicrobiology journal》2013,30(3):157-169
Anaerobic bacterial degradation of landfill waste produces a globally significant source of the greenhouse gas methane. Stable isotopic measurements of methane [δI3C(CH4) and δD(CH4)] can often fingerprint different sources of methane (natural vs. anthro‐pogenic) and help identify the bacterial processes involved in methane production. Landfill microbial communities are complex and diverse, and hence so too is the biogeochem‐istry of methane formation. To investigate the influence of (l) the methane formation pathway (acetoclastic methanogenesis and CO2 reduction), and (2) SD of water on the stable isotopic composition of landfill methane, two model butyrate‐degrading landfill systems were established. The systems were inoculated with domestic refuse from a landfill and incubated in the laboratory for 92 days. Both systems were identical except δD of water initially added to system 2 was 118% heavier than system 1. Between days 39 and 72 the systems were resupplemented with butyrate. Production of CH4 and CO2 and changes in volatile fatty acid concentration confirmed that active methanogenic populations had been established. CH4 became 13C enriched in both incubations with time. Interpreting changes in acetate, butyrate, and propionate concentration during incubation is complicated, but these observations and other information suggest that the dominant methanogenic substrate changed front CO2/H2 to acetate as the experiment progressed. This is also consistent with the observed 13C enrichment of CH4, as 13C discrimination during methane production from acetate is less than from CO2. In contrast, δD(CH4) remained relatively constant, suggesting that this measurement may not provide a reliable basis for distinguishing between CH4 from CO2 reduction and acetoclastic methanogenesis, as has previously been suggested. 相似文献
8.
Daniel C. Reed Bridget R. Deemer Sigrid van Grinsven John A. Harrison 《Biogeochemistry》2017,134(1-2):29-39
Collectively, freshwaters constitute a significant source of methane to the atmosphere, and both methane production and methane oxidation can strongly influence net emissions. Anaerobic methane oxidation (AOM) is recognized as a strong regulator of marine methane emissions and appreciation of AOM’s importance in freshwater is growing. In spite of this renewed interest, recent work and reactive-transport modeling results we present in this paper point to unresolved pathways for AOM. Comparison of recent observations from a eutrophic reservoir, Lacamas Lake, with predictions of a 1D steady-state model of water column methane dynamics indicates that high rates of methane oxidation measured via bottle assays cannot be explained with conventional electron acceptors (O2, NO2 ?, NO3 ?, SO4 2?, Mn4+, and Fe3+). Reactive-transport modeling suggests that solute oxidant concentrations at the thermocline would have to be around 10 times higher than observed to explain the measured methane consumption. Organic acids—a major constituent of organic matter—may account for part of this unexplained AOM given their abundance in eutrophic systems, although the details of these pathways remain elusive (e.g., which species are involved, seasonal renewal of reduced species, contribution of particulate versus dissolved phases). We point to several observations consistent with organic acid-mediated AOM, both in Lacamas Lake and in other systems. Nevertheless, direct evidence of this pathway is still lacking and testing for this remains an important direction for future work. To this end, we identify several new avenues of research that would help quantify the role of organic acid-mediated AOM relative to other electron acceptors. 相似文献
9.
The use of acetylene as a convenient assay substrate for nitrogenase in methane oxidising bacteria is complicated by the observation that it is a potent inhibitor of the methane monooxygenase enzyme in both whole cells and cell-free extracts. If the cells were provided with alternative oxidisable carbon substrates other than methane then nitrogen fixing cells would reduce acetylene to ethylene. Hydrogen gas also served as an oxidisable substrate in the assay. Nitrous oxide, which is reduced by nitrogenase to N2 and H2O, was not an inhibitor of methane monooxygenase function and could be used as a convenient assay substrate for nitrogenase. Reduction of both substrates by whole cells showed similar response to oxygen in the assay system and in this respect Methylococcus resembles other free living nitrogen fixing aerobes. 相似文献
10.
Kinetics of ammonia oxidation by a marine nitrifying bacterium: Methane as a substrate analogue 总被引:4,自引:0,他引:4
B. B. Ward 《Microbial ecology》1990,19(3):211-225
In pure culture, the marine ammonia oxidizer,Nitrosococcus oceanus, exhibits normal Michaelis Menten kinetics with respect to its primary substrate, ammonia.N. oceanus also exhibits a kinetic response to methane. In the absence of methane, oxidation of ammonia is first order with respect to ammonia concentration under atmospheric oxygen concentrations at seawater pH. In the presence of methane, ammonia oxidation is inhibited, and the amount of inhibition is related to the relative concentrations of methane and ammonia. Using semicontinuous batch cultures as a source of organisms for short-term kinetic experiments, I investigated the relationship between ammonia and methane oxidation inN. oceanus by varying the absolute and relative concentration of both substrates. Methane appeared to act as a substrate analogue, and its effect on ammonia oxidation was modeled as a permutation of competitive inhibition involving a cooperative enzyme system. Methane was oxidized byN. oceanus, even in the absence of measurable ammonia oxidation, but the process was inhibited at increasing methane concentrations. Of the two product pools analyzed, an average of 37% of methane oxidized was detected in particulate (cell) material and the remainder was detected in14CO2. The contribution of methane to total carbon assimilation varied with the ratio [CH4]/[NH3] and may be significant under substrate concentrations typical of a dilute aquatic environment. 相似文献
11.
Helle N. Carlsen Lars Joergensen Hans Degn 《Applied microbiology and biotechnology》1991,35(1):124-127
Summary The kinetics of methane uptake by Methylococcus capsulatus (Bath) and its inhibition by ammonia were studied by stopped-flow membrane-inlet mass spectrometry. Measurements were done on suspensions of cells grown in high- and low-copper media. With both types of cells the kinetics of methane uptake are hyperbolic when oxygen is in excess. The apparent K
m and K
max for methane uptake are both higher in low-copper cells than in high-copper cells. Ammonia is a simple competitive inhibitor of methane uptake in high-copper cells when the oxygen concentration is above a few M. The findings agree with the assumption that ammonia is a week alternative substrate for particulate methane monooxygenase. In low-copper cells the effect of ammonia is complicated and cannot be explained in terms of current assumptions on the mechanism of soluble methane monooxygenase. Our data indicate that ammonia inhibition is likely to be a more serious problem in connection with cultivation in low-copper medium than in high-copper medium.
Offprint requests to: H. N. Carlsen 相似文献
12.
《Bioinorganic chemistry》1978,8(1):1-10
Coenzyme M (2-mercaptoethanesulfonate, HSCH2CH2SO3—) reacts with methylcobalamin nonenzymatically in the pH-range between 6 and 14 to yield the S-methyl derivative (CH3SCH2CH2SO3—). In addition, and also at lower pH, methane is produced by reductive cleavage of the CoC bond. With methylcobaloximes as the methyl group donors, methane production predominates, with insignificant S-methylation. The initial rates of methane production from methylcobaloximes with coenzyme M as the reductant correlate with the rates of methane production from these substrates with active cell extracts of Methanobacterium M.o.H. 相似文献
13.
Sukhwan Yoon Jeffrey N. Carey Jeremy D. Semrau 《Applied microbiology and biotechnology》2009,83(5):949-956
Methane is a potent greenhouse gas with a global warming potential ~23 times that of carbon dioxide. Here, we describe the
modeling of a biotrickling filtration system composed of methane-consuming bacteria, i.e., methanotrophs, to assess the utility
of these systems in removing methane from the atmosphere. Model results indicate that assuming the global average atmospheric
concentration of methane, 1.7 ppmv, methane removal is ineffective using these methanotrophic biofilters as the methane concentration
is too low to enable cell survival. If the concentration is increased to 500–6,000 ppmv, however, similar to that found above
landfills and in concentrated animal feeding operations (factory farms), 4.98–35.7 tons of methane can be removed per biofilter
per year assuming biotrickling filters of typical size (3.66 m in diameter and 11.5 m in height). Using reported ranges of
capital, operational, and maintenance costs, the cost of the equivalent ton of CO2 removal using these systems is $90–$910 ($2,070–$20,900 per ton of methane), depending on the influent concentration of methane
and if heating is required. The use of methanotrophic biofilters for controlling methane emissions is technically feasible
and, provided that either the costs of biofilter construction and operation are reduced or the value of CO2 credits is increased, can also be economically attractive. 相似文献
14.
A. F. Bouwman 《Biogeochemistry》1991,15(2):65-88
Wetland rice cultivation is one of the major sources of atmospheric methane (CH4). Global rice production may increase by 65% between 1990 and 2025, causing an increase of methane emissions from a 92 Tg CH4 y–1 now to 131 Tg in 2025.Methane production depends strongly on the ratio oxidizing: reducing capacity of the soil. It can be influenced by e.g. addition of sulphate, which inhibits methanogenesis. The type and application mode of mineral fertilizers may also affect methane emissions. Addition of organic matter in the form of compost or straw causes an increase of methane emissions, but methane production is lower for materials with a low C/N ratio.High percolation rates in wetland rice soils and occasional drying up of the soil during the cultivation period depresses methane release. Water management practices aimed at reducing emissions are only feasible during specific periods in the rice growing season in flat lowland irrigated areas with high security of water availability and good control of the water supply. Intermittent drying of soils may not be possible on terraced rice lands.Assuming a 10 to 30% reduction in emission rates per unit harvested area, the global emission may amount to 93 Tg CH4 y– in 2025. A reduction of global emissions seems very difficult. To develop techniques for reducing CH4 emissions from wetland rice fields, research is required concerning interactions between soil chemical and physical properties, and soil, water and crop management and methanogenesis. Such techniques should not adversely affect rice yields. 相似文献
15.
In this paper isotope ratio mass spectrometry is used to determine the methane (CH4) oxidation fraction in the rhizosphere of intact rice plant-soil systems. Earlier studies on quantification of the methane oxidation were based on inhibition or incubation procedures which strongly interfered with the plant-soil system and resulted in a large variability of the reported fractions, while other studies considered stable isotopes at natural abundance levels to investigate methanotrophy in the rhizosphere of rice. The current work is the first that used 13C-labelled CH4 as additive and calculated the oxidation fraction from the ratio between the added 13C-labelled CH4 and its oxidation product 13CO2. Both labelled gases could be distinguished from the natural abundance percentages. The oxidation fraction for methane was found to be smaller than 7%, suggesting that former approaches overestimate the methane oxidation fraction. 相似文献
16.
Bala Yamini Sadasivam Krishna R. Reddy 《Reviews in Environmental Science and Biotechnology》2014,13(1):79-107
Mitigation of landfill gases has gained the utmost importance in recent years due to the increase in methane (CH4) emissions from landfills worldwide. This, in turn, can contribute to global warming and climatic changes. The concept of microbially mediated methane oxidation in landfill covers by using methanotrophic microorganisms has been widely adopted as a method to counter the rise in methane emissions. Traditionally, landfill soil covers were used to achieve methane oxidation, thereby reducing methane emissions. Meanwhile, the continual rise of CH4 emissions from landfills and the significant need to and importance of developing a better technology has led researchers to explore different methods to enhance microbial methane oxidation by using organic rich materials such as compost in landfill covers. The development and field application of such bio-based systems, explored by various researches worldwide, eventually led to more widely accepted and better performing cover systems capable of reducing CH4 emissions from landfills. However, the long-term performance of bio-based cover systems were found to be negatively affected by factors such as the material’s ability to self-degrade, causing CH4 to be generated rather than oxidized as well as the greater potential for forming pore-clogging exopolymeric substances. In order to design an effective cover system for landfills, it is essential to have a thorough understanding of the concepts incorporated into methodologies currently in favor along with their pros and cons. This review summarizes previous laboratory and field-scale studies conducted on various soil and bio-based cover systems, along with the modeling mechanisms adopted for quantifying CH4 oxidation rates. Finally, several issues and challenges in developing effective and economical soil and bio-based cover systems are presented. 相似文献
17.
We use a 1‐D numerical model to study the atmospheric photochemistry of oxygen, methane, and sulfur after the advent of oxygenic photosynthesis. We assume that mass‐independent fractionation (MIF) of sulfur isotopes – characteristic of the Archean – was best preserved in sediments when insoluble elemental sulfur (S8) was an important product of atmospheric photochemistry. Efficient S8 production requires three things: (i) very low levels of tropospheric O2; (ii) a source of sulfur gases to the atmosphere at least as large as the volcanic SO2 source today; and (iii) a sufficiently high abundance of methane or other reduced gas. All three requirements must be met. We suggest that the disappearance of a strong MIF sulfur signature at the beginning of the Proterozoic is better explained by the collapse of atmospheric methane, rather than by a failure of volcanism or the rise of oxygen. The photochemical models are consistent in demanding that methane decline before O2 can rise (although they are silent as to how quickly), and the collapse of a methane greenhouse effect is consistent with the onset of major ice ages immediately following the disappearance of MIF sulfur. We attribute the decline of methane to the growth of the oceanic sulfate pool as indicated by the widening envelope of mass‐dependent sulfur fractionation through the Archean. We find that a given level of biological forcing can support either oxic or anoxic atmospheres, and that the transition between the anoxic state and the oxic state is inhibited by high levels of atmospheric methane. Transition from an oxygen‐poor to an oxygen‐rich atmosphere occurs most easily when methane levels are low, which suggests that the collapse of methane not only caused the end of MIF S and major ice ages, but it may also have enabled the rise of O2. In this story the early Proterozoic ice ages were ended by the establishment of a stable oxic atmosphere, which protected a renewed methane greenhouse with an ozone shield. 相似文献
18.
Long-term growth at elevated carbon dioxide stimulates methane emission in tropical paddy rice 总被引:7,自引:0,他引:7
L. H. ZISKA† T. B. MOYA R. WASSMANN‡ O. S. NAMUCO R. S. LANTIN J. B. ADUNA E. ABAO Jr. K. F. BRONSON H. U. NEUE§ D. OLSZYK¶ 《Global Change Biology》1998,4(6):657-665
Recent anthropogenic emissions of key atmospheric trace gases (e.g. CO2 and CH4) which absorb infra-red radiation may lead to an increase in mean surface temperatures and potential changes in climate. Although sources of each gas have been evaluated independently, little attention has focused on potential interactions between gases which could influence emission rates. In the current experiment, the effect of enhanced CO2 (300 μL L–1 above ambient) and/or air temperature (4 °C above ambient) on methane generation and emission were determined for the irrigated tropical paddy rice system over 3 consecutive field seasons (1995 wet and dry seasons 1996 dry season). For all three seasons, elevated CO2 concentration resulted in a significant increase in dissolved soil methane relative to the ambient control. Consistent with the observed increases in soil methane, measurements of methane flux per unit surface area during the 1995 wet and 1996 dry seasons also showed a significant increase at elevated carbon dioxide concentration relative to the ambient CO2 condition (+49 and 60% for each season, respectively). Growth of rice at both increasing CO2 concentration and air temperature did not result in additional stimulation of either dissolved or emitted methane compared to growth at elevated CO2 alone. The observed increase in methane emissions were associated with a large, consistent, CO2-induced stimulation of root growth. Results from this experiment suggest that as atmospheric CO2 concentration increases, methane emissions from tropical paddy rice could increase above current projections. 相似文献
19.
Methanol Promotes Atmospheric Methane Oxidation by Methanotrophic Cultures and Soils 总被引:7,自引:5,他引:2
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Two methanotrophic bacteria, Methylobacter albus BG8 and Methylosinus trichosporium OB3b, oxidized atmospheric methane during batch growth on methanol. Methane consumption was rapidly and substantially diminished (95% over 9 days) when washed cell suspensions were incubated without methanol in the presence of atmospheric methane (1.7 ppm). Methanotrophic activity was stimulated after methanol (10 mM) but not methane (1,000 ppm) addition. M. albus BG8 grown in continuous culture for 80 days with methanol retained the ability to oxidize atmospheric methane and oxidized methane in a chemostat air supply. Methane oxidation during growth on methanol was not affected by methane deprivation. Differences in the kinetics of methane uptake (apparent Km and Vmax) were observed between batch- and chemostat-grown cultures. The Vmax and apparent Km values (means ± standard errors) for methanol-limited chemostat cultures were 133 ± 46 nmol of methane 108 cells−1 h−1 and 916 ± 235 ppm of methane (1.2 μM), respectively. These values were significantly lower than those determined with batch-grown cultures (Vmax of 648 ± 195 nmol of methane 108 cells−1 h−1 and apparent Km of 5,025 ± 1,234 ppm of methane [6.3 μM]). Methane consumption by soils was stimulated by the addition of methanol. These results suggest that methanol or other nonmethane substrates may promote atmospheric methane oxidation in situ. 相似文献
20.
Currently, the global annual flux of methane (CH4) to the atmosphere is fairly well constrained at ca. 645 Tg CH4 year?1. However, the relative magnitudes of the fluxes generated from different natural (e.g. wetlands, deep seepage, hydrates, ocean sediments) and anthropogenic sources remain poorly resolved. Of the identified natural sources, the contribution of vegetation to the global methane budget is arguably the least well understood. Historically, reviews of the contribution of vegetation to the global methane flux have focused on the role of plants as conduits for soil-borne methane emissions from wetlands, or the aerobic production of methane within plant tissues. Many recent global budgets only include the latter pathway (aerobic methane production) in estimating the importance of terrestrial vegetation to atmospheric CH4 flux. However, recent experimental evidence suggests several novel pathways through which vegetation can contribute to the flux of this globally important, trace greenhouse gas (GHG), such as plant cisterns that act as cryptic wetlands, heartwood rot in trees, the degradation of coarse woody debris and litter, or methane transport through herbaceous and woody plants. Herein, we synthesize the existing literature to provide a comprehensive estimate of the role of modern vegetation in the global methane budget. This first, albeit uncertain, estimate indicates that vegetation may represent up to 22 % of the annual flux of methane to the atmosphere, contributing ca. 32–143 Tg CH4 year?1 to the global flux of this important trace GHG. Overall, our findings emphasize the need to better resolve the role of vegetation in the biogeochemical cycling of methane as an important component of closing the gap in the global methane budget. 相似文献