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。     

湿地甲烷排放研究若干问题的探讨

甲烷是大气中最重要的温室气体之一,天然湿地是全球目前已知的最大排放源,每年向大气中排放的CH4约占全球CH4排放量的21％。本文就天然湿地甲烷排放研究的若干问题,包括研究方法、影响因素以及排放通量的时空变异性进行了探讨,最后对有关湿地甲烷排放模型进行了简单介绍,并对今后的研究方向提出了几点建议。     

湿地退化研究进展

受经济发展、城市扩张、气候变化的影响,湿地退化已经成为全球性现象,是当前国际湿地科学前沿领域的热点。从湿地退化标准、退化特征、退化分级、退化过程、退化机理、退化监测体系、退化评价指标与指标体系、退化监测新技术及其生态恢复理论与技术9个方面系统地介绍了当前湿地退化研究进展。结果表明湿地退化过程、退化机理、退化评价指标体系和退化湿地监测、恢复与重建研究是当前研究的重点,在未来相当长的时间内,全球气候变化、湿地退化的微观过程与机理、湿地生态系统的可持续利用将会是重要的研究方向。最后就我国当前湿地退化研究存在的问题进行了分析,并提出近期湿地退化研究亟待开展的11项研究工作,供我国湿地退化研究工作者参考。     

祁连山多年冻土区甲烷排放通量及其影响因素

全球变暖可能导致多年冻土中的有机碳分解向大气排放甲烷(CH4),但多年冻土区甲烷释放通量与环境因子的关系还不清楚.本研究于2019年6月-2020年1月,选择青藏高原北部祁连山多年冻土区,利用静态箱-气相色谱法对高寒沼泽草甸、高寒草原、高寒草甸进行CH4释放速率测定,并分析其与土壤理化性质的关系.结果表明:(1)CH4...     

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.     

互花米草入侵对滩涂湿地甲烷排放的影响

在浙江省台州市附近滩涂湿地设置3个不同互花米草入侵密度梯度,即仅有本土植物样地、互花米草与本土植物混生样地和互花米草单优群落样地,研究互花米草入侵对滩涂湿地CH₄排放的影响.结果表明: 3个样地CH₄排放通量为0.68～5.88 mg·m^-2·h^-1,CH₄排放通量随着互花米草入侵梯度的增加而显著升高,互花米草单优群落样地CH₄排放通量分别为本土植物样地和混生样地的8.7和2.3倍.互花米草入侵显著提高了产甲烷菌数量、产甲烷潜力、甲烷氧化菌数量、甲烷氧化潜力、植物生物量、土壤有机碳含量和土壤pH,降低了土壤全氮含量.CH₄排放通量与土壤全氮呈显著负相关,与产甲烷菌数量、产甲烷潜力、甲烷氧化菌数量、甲烷氧化潜力、植物生物量和土壤pH呈显著正相关.互花米草的入侵提高了滩涂湿地植物群落生物量和土壤pH,促进了产甲烷菌数量和产甲烷潜力,从而提高了滩涂湿地的CH₄排放.     

植物排放甲烷的研究进展

甲烷是一种重要的大气痕量气体,参与全球变暖和大气化学作用。传统上已知的甲烷生物排放源只有专性厌氧的原核生物即甲烷产生菌。然而近年来有研究发现,植物在好氧条件下能通过一种未知的机理排放甲烷,即非微生物机制产生甲烷。本文对植物排放甲烷的研究进展进行了综述,并提出了今后应加强研究的方面。     

潮汐作用对黄河三角洲盐沼湿地甲烷排放的影响

盐沼湿地作为陆海交互作用的过渡带是CH₄重要的自然来源。潮汐活动通过影响CH₄的产生、氧化和传输驱动了湿地CH₄间歇性、周期性的排放。利用涡度相关和微气象监测技术,对黄河三角洲一个盐地碱蓬生态系统CH₄通量、环境因子和水文要素（潮汐）进行了长期连续监测分析了该生态系统生长季CH₄排放的季节动态及潮汐作用对CH₄排放的影响。结果表明：生长季该生态系统是CH₄的排放源,排放日均值为0.063 mg m^-2 h^-1,（范围为-0.36-0.57 mg m^-2 h^-1）。潮汐淹水阶段和落潮后湿润阶段表现为CH₄的显著源。此外我们发现,短期潮汐活动引起土壤干湿状况的变化促进了CH₄脉冲式的排放,因此未来气候变化下温度升高和降雨季节分配引起的土壤干湿变化将会对该区域CH₄排放甚至碳循环产生积极影响。     

维管植物对自然湿地甲烷排放的影响

综合评述了维管植物在自然湿地甲烷产生、氧化、传输和排放过程中的作用。维管植物光合作用的产物是甲烷产生的主要碳源,植物根系的周转和碳物质的分泌为产甲烷细菌提供底物;维管植物根际氧化是甲烷氧化最主要的途径,在植物的生长期占到总氧化量的80%左右。植物传输O2的能力和根际O2的需求是影响根际氧化的主要因素;维管植物通气组织的传输促进了甲烷从土壤向大气的输送,但所采用的传输机制影响着气体的输送效率。此外,自然湿地甲烷排放的各个过程均受到维管植物形态和植被类型的影响。维管植物在甲烷排放中的作用可以部分解释自然湿地甲烷在排放的时间(季节性变化、日变化)和空间尺度上的差异。维管植物对于自然湿地甲烷排放具有指示意义,可以用于大尺度自然湿地甲烷排放量的估算。     

互花米草入侵对沿海湿地甲烷排放的影响

采集互花米草不同入侵年限(8、11和15年)的原状土壤,采用盆栽试验,研究了土壤有机碳含量对沿海湿地CH4排放的影响。结果表明,土壤有机碳含量随着互花米草入侵年限的增加而增加。在植物生长季,互花米草入侵15年的土壤有机碳含量为12.97g·kg-1,土壤CH4排放通量为2.94mg·m-2·h-1,显著高于入侵年限为8和11a(有机碳含量为8.11和9·16g·kg-1)的土壤,其土壤CH4排放通量分别为1.95和2.34mg·m-2·h-1。这主要是由于随着土壤有机碳含量提高,不仅为产甲烷菌提供了更多底物,同时也促进了产甲烷菌数量增加,从而导致更多CH4排放。因此,在评价互花米草入侵的综合环境效应时,需要兼顾土壤固碳能力和温室气体排放。     

Rising plant‐mediated methane emissions from arctic wetlands

Plant‐mediated CH₄ flux is an important pathway for land–atmosphere CH₄ emissions, but the magnitude, timing, and environmental controls, spanning scales of space and time, remain poorly understood in arctic tundra wetlands, particularly under the long‐term effects of climate change. CH₄ fluxes were measured in situ during peak growing season for the dominant aquatic emergent plants in the Alaskan arctic coastal plain, Carex aquatilis and Arctophila fulva, to assess the magnitude and species‐specific controls on CH₄ flux. Plant biomass was a strong predictor of A. fulva CH₄ flux while water depth and thaw depth were copredictors for C. aquatilis CH₄ flux. We used plant and environmental data from 1971 to 1972 from the historic International Biological Program (IBP) research site near Barrow, Alaska, which we resampled in 2010–2013, to quantify changes in plant biomass and thaw depth, and used these to estimate species‐specific decadal‐scale changes in CH₄ fluxes. A ~60% increase in CH₄ flux was estimated from the observed plant biomass and thaw depth increases in tundra ponds over the past 40 years. Despite covering only ~5% of the landscape, we estimate that aquatic C. aquatilis and A. fulva account for two‐thirds of the total regional CH₄ flux of the Barrow Peninsula. The regionally observed increases in plant biomass and active layer thickening over the past 40 years not only have major implications for energy and water balance, but also have significantly altered land–atmosphere CH₄ emissions for this region, potentially acting as a positive feedback to climate warming.     

Biogeochemistry of methane and methanogenic archaea in permafrost

This study summarizes the findings of our research on the genesis of methane, its content and distribution in permafrost horizons of different age and origin. Supported by reliable data from a broad geographical sweep, these findings confirm the presence of methane in permanently frozen fine-grained sediments. In contrast to the omnipresence of carbon dioxide in permafrost, methane-containing horizons (up to 40.0 mL kg(-1)) alternate with strata free of methane. Discrete methane-containing horizons representing over tens of thousands of years are indicative of the absence of methane diffusion through the frozen layers. Along with the isotopic composition of CH(4) carbon (delta(13)C -64 per thousand to -99 per thousand), this confirms its biological origin and points to in situ formation of this biogenic gas. Using (14)C-labeled substrates, the possibility of methane formation within permafrost was experimentally shown, as confirmed by delta(13)C values. Extremely low values (near -99 per thousand) indicate that the process of CH(4) formation is accompanied by the substantial fractionation of carbon isotopes. For the first time, cultures of methane-forming archaea, Methanosarcina mazei strain JL01 VKM B-2370, Methanobacterium sp. strain M2 VKM B-2371 and Methanobacterium sp. strain MK4 VKM B-2440 from permafrost, were isolated and described.     

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.     

Environmental and physical controls on northern terrestrial methane emissions across permafrost zones

Methane (CH₄) emissions from the northern high‐latitude region represent potentially significant biogeochemical feedbacks to the climate system. We compiled a database of growing‐season CH₄ emissions from terrestrial ecosystems located across permafrost zones, including 303 sites described in 65 studies. Data on environmental and physical variables, including permafrost conditions, were used to assess controls on CH₄ emissions. Water table position, soil temperature, and vegetation composition strongly influenced emissions and had interacting effects. Sites with a dense sedge cover had higher emissions than other sites at comparable water table positions, and this was an effect that was more pronounced at low soil temperatures. Sensitivity analysis suggested that CH₄ emissions from ecosystems where the water table on average is at or above the soil surface (wet tundra, fen underlain by permafrost, and littoral ecosystems) are more sensitive to variability in soil temperature than drier ecosystems (palsa dry tundra, bog, and fen), whereas the latter ecosystems conversely are relatively more sensitive to changes of the water table position. Sites with near‐surface permafrost had lower CH₄ fluxes than sites without permafrost at comparable water table positions, a difference that was explained by lower soil temperatures. Neither the active layer depth nor the organic soil layer depth was related to CH₄ emissions. Permafrost thaw in lowland regions is often associated with increased soil moisture, higher soil temperatures, and increased sedge cover. In our database, lowland thermokarst sites generally had higher emissions than adjacent sites with intact permafrost, but emissions from thermokarst sites were not statistically higher than emissions from permafrost‐free sites with comparable environmental conditions. Overall, these results suggest that future changes to terrestrial high‐latitude CH₄ emissions will be more proximately related to changes in moisture, soil temperature, and vegetation composition than to increased availability of organic matter following permafrost thaw.     

Role of rice in mediating methane emission

Methane emitted at different plant conditions through the different organs of rice plants was studied using a closed chamber technique under the laboratory, phytotron, and greenhouse conditions in order to clarify and quantify the role of different organs of rice plant as methane emission sites. Rice plants grown in flooded soils emit methane to the atmosphere via the aerenchyma of leaves, nodes and panicles. Emission through the rice plants is controlled by diffusion. No methane is emitted via the transpiration stream. Leaves are the major release sites at the early growth stage while nodes become more important later. Cracks and porous structure were found in the nodes. Panicles generally contribute little to methane emission. Increasing water depth temporarily reduces methane emission while concentration gradients in rice plants readjust to unsubmerged emission sites. Methane emissions in rice plants cease only when the plants become totally submerged.     

植被对多年冻土的影响研究进展

作为冰冻圈的主体,多年冻土是岩石圈与大气圈水热交换的产物,它的存在、分布及水热过程受到多种时空尺度环境因子的控制和影响.植被是生物圈的重要组成部分,是岩石圈与大气圈热量交换的媒介,它的存在和变化影响着多年冻土的水热过程和空间分布.文章综述了近几十年来植被对多年冻土影响的研究.首先,植被参与地气之间的水热周转过程,通过反射太阳辐射、贴地植被的吸水保水作用以及截留积雪作用等,对下伏冻土产生错综复杂的影响.但是不同植被类型的反射太阳辐射能力、保水与截留能力等各不相同,产生的影响大小有别.其次,同一植被类型的不同层次(如乔木层、灌木层等)对多年冻土的影响也不同,其中贴地植被产生的影响最显著.植被截留积雪,使得地面接收的太阳辐射和地表水分重分配复杂化,从而间接地影响多年冻土环境.因此当植被发生扰动后(如森林火灾和砍伐植被),就会对其所处的多年冻土环境产生各种不利影响,引发冻土灾害,甚至导致多年冻土消融.实际上植被与冻土同为寒区自然生态系统和环境的重要组成部分,它们在长期地质和生物演化中形成生态平衡.因此,植被还常常被用于指示多年冻土及其空间分布.最后提出目前研究中存在的问题,并对未来研究方向进行了展望.     

Upscaling methane fluxes from closed chambers to eddy covariance based on a permafrost biogeochemistry integrated model

Northern peatlands are a major natural source of methane (CH₄) to the atmosphere. Permafrost conditions and spatial heterogeneity are two of the major challenges for estimating CH₄ fluxes from the northern high latitudes. This study reports the development of a new model to upscale CH₄ fluxes from plant communities to ecosystem scale in permafrost peatlands by integrating an existing biogeochemical model DeNitrification‐DeComposition (DNDC) with a permafrost model Northern Ecosystem Soil Temperature (NEST). A new ebullition module was developed to track the changes of bubble volumes in the soil profile based on the ideal gas law and Henry's law. The integrated model was tested against observations of CH₄ fluxes measured by closed chambers and eddy covariance (EC) method in a polygonal permafrost area in the Lena River Delta, Russia. Results from the tests showed that the simulated soil temperature, summer thaw depths and CH₄ fluxes were in agreement with the measurements at the five chamber observation sites; and the modeled area‐weighted average CH₄ fluxes were similar to the EC observations in seasonal patterns and annual totals although discrepancy existed in shorter time scales. This study indicates that the integrated model, NEST–DNDC, is capable of upscaling CH₄ fluxes from plant communities to larger spatial scales.     

Interannual variation in methane emissions from tropical wetlands triggered by repeated El Niño Southern Oscillation

Methane (CH₄) emissions from tropical wetlands contribute 60%–80% of global natural wetland CH₄ emissions. Decreased wetland CH₄ emissions can act as a negative feedback mechanism for future climate warming and vice versa. The impact of the El Niño–Southern Oscillation (ENSO) on CH₄ emissions from wetlands remains poorly quantified at both regional and global scales, and El Niño events are expected to become more severe based on climate models’ projections. We use a process‐based model of global wetland CH₄ emissions to investigate the impacts of the ENSO on CH₄ emissions in tropical wetlands for the period from 1950 to 2012. The results show that CH₄ emissions from tropical wetlands respond strongly to repeated ENSO events, with negative anomalies occurring during El Niño periods and with positive anomalies occurring during La Niña periods. An approximately 8‐month time lag was detected between tropical wetland CH₄ emissions and ENSO events, which was caused by the combined time lag effects of ENSO events on precipitation and temperature over tropical wetlands. The ENSO can explain 49% of interannual variations for tropical wetland CH₄ emissions. Furthermore, relative to neutral years, changes in temperature have much stronger effects on tropical wetland CH₄ emissions than the changes in precipitation during ENSO periods. The occurrence of several El Niño events contributed to a lower decadal mean growth rate in atmospheric CH₄ concentrations throughout the 1980s and 1990s and to stable atmospheric CH₄ concentrations from 1999 to 2006, resulting in negative feedback to global warming.