冻土区土壤甲烷排放的研究进展及发展趋势

作为全球碳循环系统及陆地生态系统的重要组成部分,冻土区土壤甲烷排放在土壤碳库与气候变化之间的反馈联动机制中扮演着关键性角色,并因此成为全球气候变化研究中的前沿热点问题。冻土区土壤甲烷排放的气源主要为微生物产甲烷活动和冻土层、天然气水合物中的气体释放作用,其中,微生物气源的研究较为成熟,而冻土层和天然气水合物气源甲烷的排放研究目前尚停留在定性分析阶段。在影响因子方面,文献计量学统计结果中出现频次最多的关键词依次为土壤温度、湿度和水位条件、有机质含量、地表植被条件等,这些要素可以对甲烷产生、传输和氧化吸收等多个环节产生影响。模型计算法是当前冻土区土壤甲烷排放评估预测的主要方法,包括早期的统计计算模型和近年来出现的基于土壤甲烷排放成因机理的过程模型,相关计算结果有效地支撑了全球气候变化评估研究。通过对冻土区土壤甲烷排放研究成果的梳理和总结,发现当前对冻土区土壤甲烷排放的气源和单因子影响作用认识较为明确,不同尺度的监测和评估方法也较为成熟。但是,对多气源作用下的冻土区土壤甲烷复合排放研究仍然较为薄弱,尤其是在冻土层和天然气水合物的甲烷释放方面,还缺少相关的定量计算研究。与此同时,在影响因子研究方面,也缺少多因素作用下的成因机理和驱动机制分析。因此,可以通过多方法、多因素综合监测研究,利用产甲烷微生物的元基因组分析、多气源土壤甲烷排放的同位素示踪等新技术和新方法,结合卫星遥感等大尺度观测结果,完善冻土区土壤甲烷排放的过程模型。此外,作为全球的“第三极”,青藏高原区域碳循环系统的变化将对亚洲,乃至全球气候变化产生重大影响。因此,还应进一步加强对青藏高原中纬度高原冻土区土壤甲烷排放的相关研究,为区域碳排放的定量评估和全球气候变化的研究提供理论支撑。

森林土壤甲烷吸收的主控因子及其对增氮的响应研究进展

森林土壤甲烷(CH4)吸收在生态系统碳、氮循环和碳平衡研究中具有重要作用。论述了森林土壤CH4的产生和消耗过程及其主控因子,有效氮不同的森林土壤CH4吸收对氮素输入的响应差异及其驱动机制,并且明确了现有研究的不足和未来研究的重点。研究表明:大气氮沉降输入倾向于抑制富氮森林土壤的CH4吸收,而对贫氮森林土壤CH4吸收具有显著的促进作用,其内在的氮素调控机制至今尚不明确。主要的原因是过去通过高剂量施氮试验所得出的理论难以准确地解释低水平氮沉降情景下森林土壤CH4吸收过程,有关森林土壤CH4吸收对大气氮沉降响应的微生物学机理也缺乏系统性研究。未来研究的重点是探讨森林土壤CH4物理扩散和净吸收过程对施氮类型、剂量的短期与长期响应,量化深层土壤CH4累积和消耗对表层土壤CH4吸收的贡献,揭示森林土壤CH4吸收对增氮响应的物理学与生物化学机制。另外,研究森林土壤甲烷氧化菌群落活性、结构对施氮类型和剂量的响应,阐明土壤CH4吸收与甲烷氧化菌群落组成的内在联系,有助于深入揭示森林土壤CH4吸收对增氮响应的微生物学机制。

营林措施对森林土壤甲烷吸收的影响

以期为全球气候变暖背景下的林地合理经营管理提供依据。利用Scopus,Web of Science,SDOS,CNKI等数据库,查询林地土壤CH_4的相关文献,对不同营林措施(施肥、采伐、火烧、林下植被管理)森林土壤CH_4吸收通量方面的研究进行综述。施加N肥对于富氮森林土壤CH_4吸收有抑制作用,但可以显著促进贫氮森林土壤CH_4吸收;火烧后土壤CH_4吸收通量受到多种因素的影响,因此存在一定的不确定性,多数研究表明,火烧减少土壤CH_4吸收通量;皆伐改变土壤温度、含水量、有机碳的分解和利用等,从而减弱森林土壤CH_4吸收能力;择伐对森林土壤CH_4吸收的影响表现为抑制、促进和无影响;剔除林下植被提高土壤温度,加快土壤水分蒸发散失,增强CH_4氧化菌的活性,促进土壤CH_4吸收;种植固氮植物使森林土壤转变为CH_4的排放源。目前经营措施对森林土壤CH_4吸收影响的研究结果还存在较大差异,对营林措施影响森林土壤CH_4吸收的内在机理的认识还不充分。随着研究方法和观测手段的不断发展,今后应深入研究多种因素和气候变化对林地土壤CH_4吸收影响的内在机理以及甲烷氧化菌对各种干扰因素的响应机制。

艾比湖地区荒漠草地、胡杨林地土壤甲烷排放日变化规律及其环境影响因子研究

【目的】定量分析艾比湖地区荒漠草地和胡杨林地土壤甲烷排放通量的日变化,探讨影响土壤CH4排放的主要环境因子,为该地区环境因子对荒漠生态系统土壤CH4排放的影响提供一定的数据支持。【方法】采用静态暗箱法结合Li-7 700快速CH4分析仪测定荒漠草地和胡杨林地土壤生长季的甲烷排放通量,同步进行气温、风速、大气相对湿度等环境因子的观测。【结果】观测期内荒漠草地的平均通量为2.19μg/(m2·s),最大值为48.96μg/(m2·s),最小值为-38.58μg/(m2·s);胡杨林地的平均通量为-0.96μg/(m2·s),最大值为36.15μg/(m2·s),最小值为-16.82μg/(m2·s)。荒漠草地CH4排放具有较明显的昼夜变化,呈双峰曲线;胡杨林地则不明显。荒漠草地、胡杨林地土壤CH4通量排放与不同深度土壤温度之间没有固定的关系。荒漠草地甲烷通量与不同深度土壤温度的相关性高于胡杨林地,且呈极显著相关(P<0.01),而地表温度与甲烷通量相关性不强;大气相对湿度和风速与甲烷通量日变化之间相关均不显著。【结论】观测时间内的甲烷排放通量几乎为负通量,表明土壤以吸收CH4为主,故荒漠草地和胡杨林地均是甲烷的吸收汇。

南岭三种主要森林类型土壤甲烷通量研究

为对亚热带森林生态系统中土壤甲烷通量的研究提供基础数据,以南岭典型森林生态系统中常绿阔叶林(EG)、针阔混交林(EK)、山地矮林(GS)3种主要森林类型土壤为研究对象,利用地理位置的特殊性分别对南、北坡森林土壤的甲烷通量进行研究,利用静态箱法模拟试验,对土壤CH4通量及其影响因子的响应进行研究。结果表明:森林土壤甲烷通量变化是多种因素共同影响的结果,不同类型的森林,其土壤对甲烷的吸收和排放有着不同表现;南岭南、北坡均表现为甲烷汇,整体上年均甲烷通量排序为EG>GS>EK,分别为-4.326 ug/(m^2·h)、-6.025 ug/(m^2·h)和-15.406 ug/(m^2·h)。3种主要森林类型土壤甲烷通量均存在着明显的季节(月)动态变化,森林类型和月份对土壤甲烷通量影响均显著。土壤地表温度对土壤甲烷通量有显著影响,但不是影响土壤甲烷通量的主控因子。土壤湿度对不同森林类型土壤甲烷通量均有显著影响。

模拟降水减少对中亚热带杉木人工林土壤甲烷吸收的影响

森林土壤是大气中甲烷重要的汇,降水变化是影响森林土壤甲烷吸收速率(VCH4)的重要因子。以中亚热带地区不同降水减少程度的杉木林土壤为研究对象,采用静态箱气相色谱法来测定不同模拟降水减少处理样地的土壤甲烷吸收速率。结果表明:模拟降水减少后显著改变了土壤中的含水量,降水减少60%、降水减少20%和对照样地的年均土壤含水量分别为18.87%、23.89%和28.33%。杉木人工林土壤甲烷吸收速率在月变化上存在较大幅度的波动,其中土壤甲烷吸收速率在8月份达到一年中的最大值(对照75μgm^-2h^-1),2月份达到一年中的最小值(对照10.93μgm^-2h^-1)。3种处理样地的土壤全年均为甲烷汇,与对照样地的甲烷年通量(2.48kghm^-2a^-1)相比,降水减少60%和20%样地的甲烷年通量分别增加44%和19%。在对照样地中,土壤甲烷吸收速率与土壤含水量呈现负相关(P=0.001),与温度相关性不显著(P>0.05);而模拟降水减少后,土壤甲烷吸收速率与土壤温度呈正相关关系(P=0.006和P=0.034),与土壤含水量相关性不显著(P>0.05)。总之,模拟降水减少后不仅提高了杉木人工林土壤甲烷吸收的能力,同时也可能改变影响土壤甲烷吸收的环境因子;在模拟降水减少前土壤甲烷吸收速率与土壤水分相关性更为密切,而模拟降水减少后土壤甲烷吸收速率可能主要受土壤温度的影响。

中亚热带米槠天然林土壤甲烷吸收速率季节变化

以福建省建瓯市万木林自然保护区米槠天然林为对象,定位观测了土壤甲烷吸收速率(VCH4)的季节变化.结果表明:米槠天然林土壤VCH4的季节变化表现出夏秋季高于冬春季的趋势,最大值(95.13μg·m-2·h-1)出现在初秋(9月),最小值(9.13μg·m-2·h-1)出现在初春(3月).土壤全年均为甲烷汇.随土壤温度和含水量的增加,VCH4分别呈增加和降低趋势,但VCH4与土壤温度和土壤含水量的相关性均不显著.米槠天然林土壤甲烷年通量为3.93kg·hm-2·a-1,高于全球天然林土壤甲烷年通量的平均水平(2.4kg·hm-2·a-1)和亚洲地区热带天然林土壤甲烷年通量(2.07kg·hm-2·a-1),低于亚洲地区温带天然林的土壤甲烷年通量(8.12kg·hm-2·a-1).

氮输入和互花米草入侵下闽江河口潮滩土壤甲烷氧化速率研究

通过室内培养实验,研究了自然状态(对照)、外源铵态氮(NH_4Cl)和硝态氮(KNO_3)的3种浓度输入(1 g/m^2、2 g/m^2和4 g/m^2氮)和互花米草入侵下,闽江河口短叶茳芏(Cyperus malaccensis)潮滩土壤甲烷氧化速率。结果表明,与自然状态下相比,总体上,氨态氮输入促进了短叶茳芏潮滩土壤甲烷氧化,且随着氮输入浓度的增加,其促进作用逐渐增大;而硝态氮输入却抑制了短叶茳芏潮滩土壤的甲烷氧化,输入的硝态氮浓度越高,甲烷氧化速率越小;氮输入对潮滩土壤甲烷氧化速率无显著影响。互花米草(Spartina alterniflora)潮滩土壤的甲烷氧化速率高于短叶茳芏潮滩,互花米草入侵使潮滩土壤的甲烷氧化速率增加了22.66%。低、高浓度氮输入与互花米草入侵共同作用促进了潮滩土壤甲烷氧化,而中浓度氮输入与互花米草入侵共同作用却抑制了潮滩土壤甲烷氧化。潮滩土壤甲烷氧化速率与输入氮的类型、浓度、培养时间和土壤类型等有关。

土壤甲烷单加氧酶活性测定的研究

以垃圾生物覆盖土、垃圾填埋场覆盖土、菜地土为材料,研究了土壤甲烷单加氧酶(Methane monooxygenase,MMO)活性的测定条件。结果表明:0.04 g kg-1 NaN3含量可抑制土壤生物活性,可作为土壤MMO活性测定时的对照;最适的底物丙烯浓度可为0.5%;培养时间对土壤MMO活性测定影响不大,但从测定的误差和可靠性考虑,可选用5 d作为土壤MMO活性测定的培养时间。统计分析表明:采用该方法测定的土壤MMO活性与其甲烷氧化潜力有很好的线性关系。

氮肥对土壤氧化甲烷的影响研究

阐述了N肥用量、品种对土壤氧化甲垸(CH_4)的影响以及高浓度CH_4对这一影响的反作用,土壤可通过固定一定量的外源N确保土壤具有相对稳定的氧化大气CH_4能力,N含量低的土壤适量施用N肥可刺激甲烷氧化菌繁殖和功能的发挥,促进大气CH_4氧化。但当外源N用量超出一定范围时甲烷氧化菌Type Ⅰ对环境变化十分敏感,会产生抑制作用并表现为长期和短期2种效应,铵态氮具有短期更具长期效应,其直接结果是引起土壤中甲炕氧化菌尤其是Type Ⅰ数量的减少和作用的减弱,该抑制作用是单向、不可逆的。由于甲烷氧化菌Type Ⅰ和Ⅱ可被高浓度CH_4激活,不易受N肥的长期影响,有些水田土壤施用N肥甚至促进甲烷氧化菌繁殖,即N的影响是双向且可逆的。

稻-萍-鱼体系对稻田土壤环境的影响

稻-萍-鱼体系的基本技术是在单一以水稻为主体的生物群体中加入红萍和鱼类,通过对红萍和鱼的人工调控而影响整个稻田生态体系。在综合技术作用下,稻-萍-鱼体系中可混养多种鱼类,产量达4000～9800kg/hm^2;在少用50％～60％化肥、30％～50％农药、鱼沟及鱼坑占地10％～15％情况下,水稻产量比常规种稻略增,且土壤有机质、全N、全P等上升15.6％～38.5％,水稻病虫草害发生下降40.8％～99.5％,土壤甲烷(CH_4)排放量减少34.6％,显著改善了稻田生态环境。

Advances of study on atmospheric methane oxidation (consumption) in forest soil

Next to CO2, methane (CH4) is the second important contributor to global warming in the atmosphere and global atmospheric CH4 budget depends on both CH4 sources and sinks. Unsaturated soil is known as a unique sink for atmospheric CH4 in terrestrial ecosystem. Many comparison studies proved that forest soil had the biggest capacity of oxidizing atmospheric CH4 in various unsaturated soils. However, up to now, there is not an overall review in the aspect of atmospheric CH4 oxidation (consumption) in forest soil. This paper analyzed advances of studies on the mechanism of atmospheric CH4 oxidation, and re-lated natural factors (Soil physical and chemical characters, temperature and moisture, ambient main greenhouse gases con-centrations, tree species, and forest fire) and anthropogenic factors (forest clear-cutting and thinning, fertilization, exogenous aluminum salts and atmospheric deposition, adding biocides, and switch of forest land use) in forest soils. It was believed that CH4 consumption rate by forest soil was limited by diffusion and sensitive to changes in water status and temperature of soil. CH4 oxidation was also particularly sensitive to soil C/N, Ambient CO2, CH4 and N2O concentrations, tree species and forest fire. In most cases, anthropogenic disturbances will decrease atmospheric CH4 oxidation, thus resulting in the elevating of atmos-pheric CH4. Finally, the author pointed out that our knowledge of atmospheric CH4 oxidation (consumption) in forest soil was insufficient. In order to evaluate the contribution of forest soils to atmospheric CH4 oxidation and the role of forest played in the process of global environmental change, and to forecast the trends of global warming exactly, more researchers need to studies further on CH4 oxidation in various forest soils of different areas.

Advances in Greenhouse Gases Emission in Farmland Soils

[Objective] The aim was to overview the emission of greenhouse gases in farmland. [Method] Based on domestic and foreign references, production mechanism, discharging characters and major influential factors of CO2, CH4 and N2O in soils of farmland were overviewed. [Result] Production and discharge of CO2, CH. and N2O played an important role in circulation of carbon and nitrogen in terrestrial ecosystem and constituted a key method for carbon and nitrogen output. It is significant to conduct research on reduction of greenhouse gas and increase of absorption. [Conclusion] The research is beneficial for exploration on discharge rule and influential factors of greenhouse gases, providing theoretical references for reduction of greenhouse gases and study on climate change.

Effects of Nitrogen Fertilizer,Soil Moisture and Temperature on Methane Oxidation in Paddy Soil

Effects of nitrogen fertilizer,soil moisture and temperature on methane oxidation in paddy soil were investigated under laboratory conditions. Addition of 0.05 g N kg-1 soil as NH4Cl strongly inhibited methane oxidation and addition of the same rate of KCl also inhibited the oxidation but with more slight effect,suggesting that the inhibitory effect was partly caused by increase in osmotic potential in microorganism cell.Not only NH but also NO greatly affected methane oxidation.Urea did not affect methane oxidation in paddy soil in the first two days of incubation,but strong inhibitory effect was observed afterwards.Methane was oxidized in the treated soil with an optimum moisture of 280 g kg-1, and air-drying inhibited methane oxidation entirely.The optimum temperature of methane oxidation was about 30℃in paddy soil,while no methane oxidation was observed at 5℃or 50℃

Effects of Fe and Mn in Paddy Soils Derived from Different Parent Materials on Methane Production and Emission

Three types of paddy soils, derived from granite, Quaternary red clay andbasalt, respectively, were selected to study the effects of Fe and Mn in paddy soils on methaneproduction and emission through pot and incubation experiments. The results indicated that thedifference of Fe and Mn in paddy soils was one of the important factors causing obvious differencesin methane emission from different soil types. Soil Fe and Mn affecting methane emission from thepaddy soils was likely through affectingsoil Eh and forming Fe and Mn plagues on rice roots.Different rates and valences of added Fe and Mn significantly affected methane production from paddysoils. Therefore, this study enhanced understanding of processes controlling methane emission frompaddy soils and may help to improve modeling and estimating regional and global methane emissionfrom paddy soils.

Effects of Organic Manure Applications on Methane and Nitrous Oxide Emissions in Paddy Fields

This study was carried out in paddy fields to explore how organic manure applications would affect greenhouse emissions in South China. The results showed that the seasonal emission of CH4 under the chemical fertilizer （CF） treatment was 271.47 kg/hm^2. In comparison, the seasonal emissions of CH4 under the treatment of pig manure （PM）, chicken manure （CM） and rice straw （RS） increased by 50.61,260.22 and 602.82 kg/hm^2, respectively. N2O emission under the CF treatment was 1.22 kg/hm^2, while the N20 seasonal emissions under tile PM, CM and RS treatment decreased by 23.6% （P〈0.05）, 31.7% （P〈0.05） and 30.9% （P〈0.05）, respectively. Meanwhile, the readily oxidized organic carbon （which was oxidized by 167 mmol/L potassium permanganate, ROC167） of manure, paddy soil Eh value and temperature could also affect the CH4 emissions. The average yield of the organic fertilizer treatments increased by 6.8% compared with that of the CF treatment. Among all the organic fertilizer treatments, the PM treatment offered the lowest global warming potential and greenhouse gas intensity, in which the PM was of no significant difference from NF （no fertilizing） and CF. Therefore, the pig manure is capable of coordinating the relationship between environment and yield, and it also has a low ROC167 content, so the PM is considered worthy of recommendation.

Profile of Methane Concentrations in Soil and Atmosphere in Alpine Steppe Ecosystem on Tibetan Plateau

The methane concentration profile from -1.5m depth in soil to 32m height in air was measured in alpine steppe lo-cated in the permafrost area. Methane concentrations showed widely variations both in air and in soil during the study period. The mean concentrations in atmosphere were all higher than those in soil, and the highest methane concentration was found in air at the height of 16m with the lowest concentration occur-ring at the depth of 1.5m in soil. The variations of atmospheric methane concentrations did not show any clear pattern both temporally and spatially, although they exhibited a more steady-stable state than those in soil. During the seasonal variations, the methane concentrations at different depths in soil were sig-nificantly correlated (R2>0.6) with each other comparing to the weak correlations (R2<0.2) between the atmospheric concentra-tions at different heights. Mean methane concentrations in soil significantly decreased with depth. This was the compositive influence of the decreasing production rates and the increasing methane oxidation rates, which was caused by the descent soil moisture with depth. Although the methane concentrations at all depths varied widely during the growing season, they showed very distinct temporal variations in the non-growing season. It was indicated from the literatures that methane oxidation rates were positively correlated with soil temperature. The higher methane concentrations in soil during the winter were deter-mined by the lower methane oxidation rates with decreasing soil temperatures, whereas methane production rates had no reaction to the lower temperature. Relations between methane contribution and other environmental factors were not discussed in this paper for lacking of data, which impulse us to carry out further and more detailed studies in this unique area.

Methanogenesis and Methanotrophy in Soil: A Review

Global warming, as a result of an increase in the mean temperature of the planet, might lead to catastrophic events for humanity. This temperature increase is mainly the result of an increase in the atmospheric greenhouse gases （GHG） concentration. Water vapor, carbon dioxide （CO2）, methane （CH4） and nitrous oxide （N20） are the most important GHG, and human activities, such as industry, livestock and agriculture, contribute to the production of these gases. Methane, at an atmospheric concentration of 1.7 gmol tool-1 currently, is responsible for 16% of the global warming due to its relatively high global warming potential. Soils play an important role in the CH4 cycle as methanotrophy （oxidation of CH4） and methanogenesis （production of CH4） take place in them. Understanding methanogenesis and methanotrophy is essential to establish new agriculture techniques and industrial processes that contribute to a better balance of GHG. The current knowledge of methanogenesis and methanotrophy in soils, anaerobic CH4 oxidation and methanotrophy in extreme environments is also discussed.

Chronosequencing methanogenic archaea in ancient Longji rice Terraces in China

Chronosequences of ancient rice terraces serve as an invaluable archive for reconstructions of historical human-environment interactions. Presently, however, these reconstructions are based on traditional soil physico-chemical properties. The microorganisms in palaeosols have been unexplored. We hypothesized that microbial information can be used as an additional proxy to complement and consolidate archaeological interpretations. To test this hypothesis, the palaeoenvironmental methanogenic archaeal DNA in Longji Terraces, one of the famous ancient terraces in China, dating back to the late Yuan Dynasty(CE1361–1406), was chronosequenced by high-throughput sequencing. It was found that the methanogenic archaeal abundance, diversity and community composition were closely associated with the 630 years of rice cultivation and in line with changes in multi-proxy data. Particularly, the centennial-and decadalscale influences of known historical events, including social turbulences(The Taiping Rebellion, CE1850–1865), palaeoclimate changes(the Little Ice Age) and recorded natural disasters(earthquakes and inundation), on ancient agricultural society were clearly echoed in the microbial archives as variations in alpha and beta diversity. This striking correlation suggests that the microorganisms archived in palaeosols can be quantitatively and qualitatively analyzed to provide an additional proxy, and palaeo-microbial information could be routinely incorporated in the toolkit for archaeological interpretation.