好氧甲烷氧化菌生理生态特征及其在自然湿地中的群落多样性研究进展

甲烷氧化菌是一类可以利用甲烷作为唯一碳源和能源的细菌,在全球变化和整个生态系统碳循环过程中起着重要的作用。近年来,对甲烷氧化菌的生理生态特征及其在自然湿地中的群落多样性研究取得了较大进展。在分类方面,疣微菌门、NC10门及两个丝状菌属甲烷氧化菌的发现使其分类体系得到了进一步的完善;在单加氧酶方面,发现甲烷氧化菌可以利用pM MO和sM MO两种酶进行氧化甲烷的第一步反应,Ⅱ型甲烷氧化菌中pM MO2的发现证实甲烷氧化菌可以利用这种酶氧化低浓度的甲烷;在底物利用方面,已经发现了越来越多的兼性营养型甲烷氧化菌,证实它们可以利用的底物比之前认为的更广泛,其中包括乙酸等含有碳碳键的化合物;在生存环境方面,能在不同温度、酸度和盐度的环境中生存的甲烷氧化菌不断被分离出来。全球自然湿地甲烷氧化菌群落多样性的研究目前主要集中在北半球高纬度的酸性泥炭湿地,Ⅱ型甲烷氧化菌Methylocystis、Methylocella和Methylocapsa是这类湿地主要的甲烷氧化菌类群,尤其以Methylocystis类群最为广泛,而Ⅰ型甲烷氧化菌尤其是Methylobacter在北极寒冷湿地中占优势。随着高通量测序时代的到来和新的分离技术的发展,对甲烷氧化菌的现有认识将面临更多的挑战和发展。     

Methane emissions from wetlands: biogeochemical,microbial, and modeling perspectives from local to global scales

Understanding the dynamics of methane (CH₄) emissions is of paramount importance because CH₄ has 25 times the global warming potential of carbon dioxide (CO₂) and is currently the second most important anthropogenic greenhouse gas. Wetlands are the single largest natural CH₄ source with median emissions from published studies of 164 Tg yr^?1, which is about a third of total global emissions. We provide a perspective on important new frontiers in obtaining a better understanding of CH₄ dynamics in natural systems, with a focus on wetlands. One of the most exciting recent developments in this field is the attempt to integrate the different methodologies and spatial scales of biogeochemistry, molecular microbiology, and modeling, and thus this is a major focus of this review. Our specific objectives are to provide an up‐to‐date synthesis of estimates of global CH₄ emissions from wetlands and other freshwater aquatic ecosystems, briefly summarize major biogeophysical controls over CH₄ emissions from wetlands, suggest new frontiers in CH₄ biogeochemistry, examine relationships between methanogen community structure and CH₄ dynamics in situ, and to review the current generation of CH₄ models. We highlight throughout some of the most pressing issues concerning global change and feedbacks on CH₄ emissions from natural ecosystems. Major uncertainties in estimating current and future CH₄ emissions from natural ecosystems include the following: (i) A number of important controls over CH₄ production, consumption, and transport have not been, or are inadequately, incorporated into existing CH₄ biogeochemistry models. (ii) Significant errors in regional and global emission estimates are derived from large spatial‐scale extrapolations from highly heterogeneous and often poorly mapped wetland complexes. (iii) The limited number of observations of CH₄ fluxes and their associated environmental variables loosely constrains the parameterization of process‐based biogeochemistry models.     

Methane emissions from wet grasslands on peat soil in a nature preserve

The area of wet grasslands on peat soil in the Netherlands is slowly increasing at the expense of drained, agriculturally used grasslands. This study aimed (i) to assess the contribution of wet grasslands on peat soil to methane (CH₄) emissions, and (ii) to explain differences among sites and between years in order to improve our understanding of controlling factors. For these purposes, a field study was conducted in the period 1994–1996 in the nature preserve Nieuwkoopse Plassen, which is a former peat mining and agricultural area. Net CH₄ emissions were measured weekly to monthly with vented closed flux chambers at three representative sites, and at ditches near these sites. Three-years average of CH₄ emissions was 7.9 g CH₄ m^–2 yr^–1 for Drie Berken Zudde, 13.3 for Koole, and 20.4 for Brampjesgat. Ditches near the sites emitted 4.2–22.5 g CH₄ m^–2 yr^–1. The time-course of CH₄ emissions for all experimental sites and years was fit with a multiple linear regression model with ground water level and soil temperature as independent variables. Lowering or raising the ground water level by 5 cm could decrease or increase CH₄ emissions by 30–50%. Therefore, ground water level management of these grasslands should be done with care.     

Archaea in metazoan diets: implications for food webs and biogeochemical cycling

Although the importance of trophic linkages, including ‘top-down forcing'', on energy flow and ecosystem productivity is recognized, the influence of metazoan grazing on Archaea and the biogeochemical processes that they mediate is unknown. Here, we test if: (1) Archaea provide a food source sufficient to allow metazoan fauna to complete their life cycle; (2) neutral lipid biomarkers (including crocetane) can be used to identify Archaea consumers; and (3) archaeal aggregates are a dietary source for methane seep metazoans. In the laboratory, we demonstrated that a dorvilleid polychaete, Ophryotrocha labronica, can complete its life cycle on two strains of Euryarchaeota with the same growth rate as when fed bacterial and eukaryotic food. Archaea were therefore confirmed as a digestible and nutritious food source sufficient to sustain metazoan populations. Both strains of Euryarchaeota used as food sources had unique lipids that were not incorporated into O. labronica tissues. At methane seeps, sulfate-reducing bacteria that form aggregations and live syntrophically with anaerobic-methane oxidizing Archaea contain isotopically and structurally unique fatty acids (FAs). These biomarkers were incorporated into tissues of an endolithofaunal dorvilleid polychaete species from Costa Rica (mean bulk δ¹³C=−92±4‰ polar lipids −116‰) documenting consumption of archaeal-bacterial aggregates. FA composition of additional soft-sediment methane seep species from Oregon and California provided evidence that consumption of archaeal-bacterial aggregates is widespread at methane seeps. This work is the first to show that Archaea are consumed by heterotrophic metazoans, a trophic process we coin as ‘archivory''.     

Carbon, nitrogen and phosphorus cycling in rivermarginal wetlands; a model examination of landscapegeochemical flows

The importance of landscape geochemical flows wasinvestigated using a dynamic model simulating carbon,nitrogen and phosphorus cycling in riverine wetlands,which has been described in a previous paper. Thehydro-geomorphic unit (HGMU) concept was incorporatedin the model by defining a separate, completeunit-model for each unit (HGMU) within the wetland.These unit-models were connected by defining the flowsof nitrogen and phosphorus between them. These flows,also called landscape geochemical flows, usuallyconsist of flows of water containing N and P.The model was applied to a site at Kismeldon Meadows,in south-western England. This site consists of twounits, a slope and a floodplain, separated by a ditch,which catches most of the run off and shallowgroundwater flows from the slope. Only an estimated1% of the N and P that leaves the slope unit in thewater outflow reaches the floodplain unit; the rest iscaught in the system of ditches, which prevent thegeochemical flows taking their natural course. Toexamine the influence of this system of ditches, themodel was run for the same site, but without theditches. This is comparable to a situation of arestored site, where run off and shallow groundwaterflows containing nutrients, can freely get from theslope to the floodplain.The computer simulation experiment reconnecting theslope and floodplain showed that this (1) increasedthe nutrient input into the floodplain, causing ahigher biomass production, and (2) increased thewetness of the floodplain, causing slowerdecomposition, which together (3) led to a faster soilorganic matter accumulation in the floodplain.Nutrient inflows became relatively more importantcompared to atmospheric deposition, especially forphosphorus. By connecting the slope and the floodplainmore nitrogen and less phosphorus flowed into theriver.     

The use of fluorogenic substrates for measuring enzyme activity in peatlands

The fluorogenic model substrates, methylumbelliferyl [MUF]-β-D-glucoside, MUF-phosphate and MUF-sulphate, were used to investigate the activities of β-glucosidase, phosphatase and sulphatase, respectively, in Welsh peatland soils. The method was used to investigate depth dependent variations in enzyme activity in a riparian wetland, and flush channel wetland. The highest activities were found at depths of less than 10 cm, thus confirming other studies which suggest this upper depth to be the site of greatest microbial activity. The most serious limitation to the technique was found to be the (fluorescence) quenching effects of the phenolic materials that dominate peatland dissolved organic carbon. The problem necessitates the adoption of a time consuming quench correction procedure with every sample. Fluorogenic substrates have led to a greater understanding of the role of enzymes in other aquatic systems. It seems likely that they will prove of equal value in elucidating their role in nutrient cycling and the biogeochemistry of peatlands.     

白骨壤模拟湿地系统中磷的分配循环及其净化效应

在温室中建立红树林植物白骨壤模拟湿地系统 ,分别用正常、5倍和 10倍 3种不同浓度的人工配置的污水每周定时定量对模拟系统进行污灌 1a。研究营养污染物 P在系统中的分配、循环及其被净化的效果。结果表明 :随污水处理浓度的升高 ,被更换的潮汐水中的含 P量和土壤含 P量都有明显提高 ;植物体各部分含 P量的高低顺序排列为 :叶 >茎 >根 ;在植物 -土壤系统中4个组分 CA0 、CA1 、CA5和 CA1 0 植物中 P元素的周转期依次为 4 .70 a、4 .6 1a、3.80 a和 5 .4 4 a;模拟植物 -土壤系统对污水中 P的净化效果显著 ,CA1 、CA5和 CA1 0 组的净化率分别为 81.2 3%、94 .4 0 %和 95 .6 3%。     

白骨壤模拟湿地系统中Pb的分布、迁移及其净化效应

在温室中建立红树林植物白骨壤模拟湿地系统,分别用正常(NW)、5倍(FW)和10倍(TW)浓度人工配置的城市污水每周定时定量对模拟系统污灌2次,用海水作对照(CL),持续1年。研究重金属Pb在湿地系统中的分布、迁移及其被净化的效果。结果表明：加入系统中的Pb主要存留于土壤子系统中,很少迁移到植物体和凋落物中：植物各器官中的Pb含量在根中最高;模拟系统对重金属。Pb的净化效果显著,各污水处理组分别为：NW组97．97％、FW组97．86％、TW组98．06％。根据物质平衡模型计算得土壤子系统。Pb的环境容量较大,因此整个模拟系统对Pb污染的承受力较大。     

扎龙芦苇湿地生长季的甲烷排放通量

为研究高寒地区天然淡水芦苇湿地的甲烷排放特征,采用静态箱-气相色谱法,测定了扎龙不同水位芦苇湿地生长季的甲烷排放通量.结果表明:观测期内,扎龙芦苇湿地甲烷排放通量平均为7.67 mg·m^-2·h^-1（-21.18～46.15 mg·m^-2·h^-1）,其中深水区(平均水深100 cm)和浅水区(平均水深25 cm)的平均甲烷排放通量分别为5.81和9.52 mg·m^-2·h^-1,排放峰值分别出现在8月和7月,最低值均出现在10月.深水区夏季(6-7月)的甲烷排放通量显著低于浅水区,而春(5月)、秋(8-10月)季节显著高于浅水区.生长季甲烷排放通量的变化为夏季>秋季>春季;昼夜排放量为12:00和14:00最高,0:00最低.温度和水位是高寒地区淡水芦苇湿地甲烷排放通量变化的主要影响因子.     

内陆湿地与水体甲烷厌氧氧化功能微生物研究进展

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^-、SO₄^2-、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。     

Opposing seasonal temperature dependencies of CO2 and CH4 emissions from wetlands

Wetlands are critically important to global climate change because of their role in modulating the release of atmospheric greenhouse gases (GHGs) carbon dioxide (CO₂) and methane (CH₄). Temperature plays a crucial role in wetland GHG emissions, while the general pattern for seasonal temperature dependencies of wetland CO₂ and CH₄ emissions is poorly understood. Here we show opposite seasonal temperature dependencies of CO₂ and CH₄ emissions by using 36,663 daily observations of simultaneous measurements of ecosystem-scale CO₂ and CH₄ emissions in 42 widely distributed wetlands from the FLUXNET-CH₄ database. Specifically, the temperature dependence of CO₂ emissions decreased with increasing monthly mean temperature, but the opposite was true for that of CH₄ emissions. Neglecting seasonal temperature dependencies may overestimate wetland CO₂ and CH₄ emissions compared to the use of a year-based static and consistent temperature dependence parameter when only considering temperature effects. Our findings highlight the importance of incorporating the remarkable seasonality in temperature dependence into process-based biogeochemical models to predict feedbacks of wetland GHG emissions to climate warming.     

不同干扰因素对森林和湿地温室气体通量影响的研究进展

森林和湿地是CO2、CH4和N2O等温室气体重要的源、汇和转换器,在全球气候变化过程中起着重要作用。森林和湿地温室气体通量受到诸多因子的作用,其中干扰便是一个重要的因素。不同干扰因素对于森林和湿地生态系统温室气体通量的影响,国际上已经开展了相应的研究。基于人为和自然两大类干扰方式,分别从采伐、施肥、垦殖等人为干扰因素和火烧、台风(飓风)等自然干扰因素综述了干扰对于森林和湿地生态系统CO2、CH4和N2O通量的影响。根据目前研究中存在的不足,提出了今后应需加强的领域,以期更好地揭示干扰对于森林和湿地生态系统温室气体通量的影响及作用机制,为今后深入开展相关研究提供一定的参考价值。     

Methane production and methane consumption: a review of processes underlying wetland methane fluxes

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.     

Succession and herbivory in monsoonal wetlands

This paper considers the applicability of the Gleasonian succession model to monsoonal wetlands, particularly those in Australia and India. The similarities in climate and taxa shared among these wetlands produce a setting in which successional cycles may be replicated. The Gleasonian succession model was first designed to describe cyclic changes in prairie pothole wetlands in response to water flux and herbivore activity over 5–25 year intervals. However, monsoonal wetlands change over an annual cycle. The Gleasonian succession may therefore be faster in these wetlands than in temperate ones. Herbivores create openings in flooded vegetation during the wet season in India by killing emergent species. During the dry season, Paspalum distichum revegetates these openings via the sprouting of vegetative fragments (VS-I; establishment by vegetative means in drawndown conditions). In Australia, in those monsoonal wetlands dominated by the annual Oryza meridionalis (AS-II; establishment by seed germination in flooded conditions), revegetation is from the seed bank during the wet season. The Gleasonian succession model can help to explain the invasion of exotics in monsoonal wetlands; in Australia, sites dominated by Oryza meridionalis (wet season annual) can be invaded during the dry season by Mimosa pigra (PS-I; perennial, establishment by seed germination in drawndown conditions). Thus the role of herbivores in succession is more complicated than current predictive models of vegetation change encompass. Herbivores select specific habitats over plant species, and also can form symbiotic relationships with plants as seed dispersers. Nonetheless, if appropriately modified with respect to the life history requirements of these plant species, the Gleasonian succession model is useful in describing annual and long-term changes in the vegetation of monsoonal wetlands.     

Nitrous oxide emissions from a gully mire in mid-Wales, UK, under simulated summer drought

Certain general circulation models predict that a doubling of atmospheric carbon dioxide concentrations will increase the frequency of summer drought in northern wetlands due to hotter, drier summers. There is currently much uncertainty as to how drought will affect emissions of the greenhouse gas, nitrous oxide, from wetlands. We have demonstrated that an eight centimetre drawdown of the water table in a gully mire does not significantly affect nitrous oxide emissions from this site. However, under a more extreme drought scenario carried out on peat monoliths, nitrous oxide emissions increased exponentially with a linear decrease in water table height. Drought caused a significant increase in nitrous oxide productionbelow the water table but most of the total increase could be attributed to increased emissionsabove the water table. Results from an acetylene block experiment suggested that increased emissions were caused by increased nitrous oxide production from denitrification, rather than by increased production from nitrification. In the laboratory study, drought severity had no effect on peatwater nitrate concentrations below the water table, however, increasing drought severity decreased ammonium concentrations.     

Aquatic macroinvertebrate assemblages in mitigated and natural wetlands

Many wetlands have been constructed in West Virginia as mitigation for a variety of human disturbances, but no comprehensive evaluation on their success has been conducted. Macroinvertebrates are extremely valuable components of functioning wetland ecosystems. As such, benthic and water column invertebrate communities were chosen as surrogates for wetland function in the evaluation of 11 mitigation and 4 reference wetlands in West Virginia. Mitigation wetlands ranged in age from 4 to 21 years old. Overall familial richness, diversity, density and biomass were similar between mitigation and reference wetlands (p > 0.05). Within open water habitats, total benthic invertebrate density was higher in reference wetlands, but mass of common taxa from water column samples was higher in mitigation wetlands (p < 0.05) Planorbidae density from benthic samples in emergent habitats was higher in reference than mitigated wetlands. Benthic Oligochaeta density was higher across open water habitats in mitigation wetlands. All other benthic taxa were similar between wetland types. Among the most common water column orders, Isopoda density was higher in reference wetlands, but Physidae density was higher in mitigation wetlands. Within mitigation wetlands, emergent areas contained higher richness and diversity than open areas. These data indicate that mitigation and reference wetlands generally support similar invertebrate assemblages, especially among benthic populations. The few observed differences are likely attributable to differences in vegetative community composition and structure. Mitigation wetlands currently support abundant and productive invertebrate communities, and as such, provide quality habitat for wetland dependent wildlife species, especially waterbirds and anurans.