食气梭菌的研究进展

食气梭菌是一类主要的化能自养微生物,可利用二氧化碳(CO_2)和一氧化碳(CO)合成多种化学品和燃料,具有良好的工业应用前景。天然的食气梭菌吸收、固定和转化一碳气体速率较慢,能量代谢效率低且高值产物种类少。近年来,随着组学、分子遗传学工具以及生化分析技术的快速发展,食气梭菌的生理代谢特点及其相关分子机制、代谢工程设计、改造和发酵工艺等方面都得到广泛而深入的研究。本文针对近年来食气梭菌的研究进展进行了梳理和总结,以期能为这类重要工业微生物的基础和应用研究,以及一碳气体的生物转化利用提供参考。     

设施菜田不同碳氮管理对反硝化菌结构和功能的影响

【目的】通过6年长期定位试验,比较设施菜田不同碳氮管理下反硝化菌结构和功能的差异。【方法】采用末端限制性片段多态性(T-RFLP)和变性梯度凝胶电泳(DGGE)方法分别分析nir K/nir S和nos Z型反硝化菌群结构特征,利用自动连续在线培养监测体系(Robot系统)测定分析NO/(NO3-+NO2-)和N2O/(N2O+N2)产物比,并通过乙炔抑制法测定反硝化酶活性。【结果】传统施肥处理(CN)显著改变了nir K和nos Z型反硝化菌的结构,增加了NO/(NO3-+NO2-)和N2O/(N2O+N2)产物比。nir S型菌受碳氮管理影响较小。减氮(RN)和添加秸秆处理(RN+S)的nir K和nos Z型反硝化菌结构与CN处理的差异性显著,且会显著降低NO/(NO3-+NO2-)和N2O/(N2O+N2)产物比;与CN和RN相比,RN+S显著增加反硝化酶活性。【结论】设施菜田长期传统施肥措施改变了反硝化菌的结构和功能,增加土壤自身的NO产生能力并减弱了N2O还原N2的能力。减氮和添加秸秆管理能形成自身的反硝化菌群结构,并降低NO和N2O排放风险;秸秆的添加会促进反硝化潜在速率,降低菜田NO3-淋洗风险。     

马尾松幼苗根系和光合碳供应对土壤性质变化和温室气体排放的驱动作用

森林植被受全球气候变化、森林经营活动及病虫害等多种干扰,导致林地光合碳供应水平及根系输入量发生变化。在此背景下,土壤性质及土壤温室气体排放的响应及其机理是预测森林碳汇功能变化及森林可持续经营的重要依据。以2年生马尾松盆栽苗为对象,通过单株/盆和3株/盆栽植密度控制根系输入量、通过环割和截干控制光合碳向地下的供应能力,模拟森林植被干扰导致的根系输入量及光合碳供应变化对土壤理化性质、微生物群落结构及温室气体排放的影响。结果表明,苗木根系非结构性碳水化合物(TNC)含量和氮含量比单株/盆低;3株/盆的土壤速效氮含量比单株/盆低,土壤革兰氏阳性菌、厌氧菌、放线菌及丛枝菌根真菌丰富度均比单株/盆显著增加,3株/盆的土壤二氧化碳(CO₂)排放速率较高,但土壤氧化亚氮(N₂O)排放速率差异不显著。无论是单株/盆还是3株/盆,环割和截干处理后,根系生物量、根系长度及表面积均比对照显著下降;根系TNC含量显著下降。土壤和根系氮含量都有增加趋势;土壤微生物生物量碳(SMBC)含量降低,而土壤微生物生物量氮(SMBN)则提高。环割和截干后,土壤中各种微生物组成丰富度均有下降趋势,土壤CO₂排放速率显著下降,土壤N₂O排放速率则显著提高。根系输入量及光合碳供应对土壤细菌和真菌含量均有显著影响,土壤细菌含量与根系生物量、SMBC和SMBN显著正相关;土壤真菌含量与土壤温度显著负相关,与根系生物量、SMBC和SMBN显著正相关。相关分析表明,土壤CO₂排放通量与土壤温度、土壤湿度及根系生物量显著正相关,与土壤硝态氮显著负相关;土壤N₂O排放通量与土壤温度和土壤湿度显著正相关。以上研究表明,根系输入量与地上光合碳供应共同作用,改变土壤理化性质及微生物环境,进而影响土壤温室气体排放。     

草地农业生态系统的碳平衡分析方法

根据草地农业生态系统的结构,它的碳平衡为4个生产层的碳平衡之和,也是3个界面的碳平衡之和,而某一生产层或者某一界面的碳平衡则是其固定、输入、排放和输出的碳之和。草地农业生态系统4个生产层的碳平衡分析方法定量重要生产环节的碳汇与碳源过程,便于草业生产改进碳汇管理;草地农业生态系统3个界面的碳平衡分析方法显示碳源和碳汇的发生机理,及其空间和数量关系,便于调控草业生产组分以增汇减排;但是,这两个方法不易区分碳的来源和去向,难以明确其利用效率。草地农业生态系统碳平衡分析的输入/输出法定量地指示碳的来源和去向,以及碳效率,计算简单,但是较为概括,不利于牧场尺度的草业碳汇管理。以中国祁连山甘肃马鹿牧场和澳大利亚塔斯玛尼亚奶牛牧场为例,用3种方法分析了两个牧场的碳平衡,结果表明,放牧管理的草业系统的主要碳源是休闲旅游、产品加工流通环节产生的温室气体,主要碳汇是草地和土壤中贮存的碳,好的草地管理可以增汇减排。     

Immediate and long-term nitrogen oxide emissions from tropical forest soils exposed to elevated nitrogen input

Tropical nitrogen (N) deposition is projected to increase substantially within the coming decades. Increases in soil emissions of the climate‐relevant trace gases NO and N₂O are expected, but few studies address this possibility. We used N addition experiments to achieve N‐enriched conditions in contrasting montane and lowland forests and assessed changes in the timing and magnitude of soil N‐oxide emissions. We evaluated transitory effects, which occurred immediately after N addition, and long‐term effects measured at least 6 weeks after N addition. In the montane forest where stem growth was N limited, the first‐time N additions caused rapid increases in soil N‐oxide emissions. During the first 2 years of N addition, annual N‐oxide emissions were five times (transitory effect) and two times (long‐term effect) larger than controls. This contradicts the current assumption that N‐limited tropical montane forests will respond to N additions with only small and delayed increases in soil N‐oxide emissions. We attribute this fast and large response of soil N‐oxide emissions to the presence of an organic layer (a characteristic feature of this forest type) in which nitrification increased substantially following N addition. In the lowland forest where stem growth was neither N nor phosphorus (P) limited, the first‐time N additions caused only gradual and minimal increases in soil N‐oxide emissions. These first N additions were completed at the beginning of the wet season, and low soil water content may have limited nitrification. In contrast, the 9‐ and 10‐year N‐addition plots displayed instantaneous and large soil N‐oxide emissions. Annual N‐oxide emissions under chronic N addition were seven times (transitory effect) and four times (long‐term effect) larger than controls. Seasonal changes in soil water content also caused seasonal changes in soil N‐oxide emissions from the 9‐ and 10‐year N‐addition plots. This suggests that climate change scenarios, where rainfall quantity and seasonality change, will alter the relative importance of soil NO and N₂O emissions from tropical forests exposed to elevated N deposition.     

高寒草地土壤温室气体排放对放牧的响应研究进展

高寒草地生态系统具有独特的地理环境和气候特征,对放牧干扰十分敏感,在全球温室气体通量中贡献突出,研究高寒草地放牧对土壤温室气体排放的影响机制具有重要意义。本文总结高寒草地温室气体源/汇特征、不同放牧方式对土壤微环境和微生物群落结构的影响,发现高寒草地主要是CO₂源、CH₄汇、N₂O源。放牧通过家畜选择性采食、践踏和排泄物返还等多重机制作用于地上植物、土壤结构、温度、湿度和养分,进而影响地下微生物及温室气体通量。本文旨在为高寒草地生态系统健康发展和管理及缓解全球气候变化提供科学依据,并对未来研究方向进行展望。     

微塑料对稻田土壤温室气体排放和微生物群落的影响

微塑料因在土壤环境中广泛存在及其潜在的生态风险而受到越来越多的关注。微塑料的赋存会改变土壤理化性质,并对土壤微生物群落及其驱动的生物地球化学过程产生影响,而相关研究尚处于起步阶段。可生物降解塑料作为传统塑料的替代品,越来越多地应用于农业活动,并释放到土壤中。然而,可生物降解微塑料对土壤微生物特性产生影响的研究鲜有报道。基于此,本试验以我国三江平原水稻田土壤为研究对象,选取了2种常见的微塑料为试验材料,分别为传统型微塑料聚丙烯(Polypropylene,PP)和可降解微塑料聚乳酸(Polylactic acid,PLA),进行了为期41d的微宇宙培养实验,旨在分析不同浓度与类型的微塑料对土壤可溶性有机碳(Dissolved Organic Carbon,DOC)含量及官能团特征、温室气体排放以及微生物群落结构的差异性影响。结果表明,传统型微塑料PP与可降解微塑料PLA添加均对土壤理化性质与微生物群落产生显著影响。其中,微塑料添加大体上增加了土壤DOC含量,PLA的促进作用较为明显,且增加含量与微塑料添加量呈正相关;PP和PLA均影响土壤DOC分子结构,削弱了土壤团聚化程度并促进了大分子量DOC化合物的生成;微塑料的添加促进土壤CH₄排放,而有效抑制了土壤CO₂排放;微塑料显著改变了土壤细菌和真菌群落的丰富度与多样性。相关分析结果表明,土壤CO₂累计排放量与芳香族化合物结构及疏水性等官能团特征、变形菌门(Proteobacteria)与放线菌门(Actinobacteria)均呈显著正相关关系。以上结果表明,微塑料添加改变了土壤DOC含量及官能团特征与微生物环境,进而影响土壤温室气体排放。本研究为今后微塑料对土壤地球化学和微生物特性的影响研究提供了科学的思路,同时也有助于评估微塑料对土壤生态系统的生态风险。     

Impact of Updated Material Production Data in the GREET Life Cycle Model

The Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET) model developed by Argonne National Laboratory quantifies the life cycle energy consumption and air emissions resulting from the production and use of light‐duty vehicles in the United States. GREET is comprised of two components: GREET 1 represents the fuel cycle of various energy carriers, including automotive fuels, and GREET 2 represents the vehicle cycle, which accounts for the production of vehicles and their constituent materials. The GREET model was updated in 2012 and now includes higher‐resolution material processing and transformation data. This study evaluated how model updates influence material and vehicle life cycle results. First, new primary energy demand and greenhouse gas (GHG) emissions results from GREET 2 for steel, aluminum, and plastics resins are compared herein with those from the previous version of the model as well as industrial results. A part of the comparison is a discussion about causes of differences between results. Included in this discussion is an assessment of the impact of the new material production data on vehicle life cycle results for conventional internal combustion engine (ICE) vehicles by comparing the energy and GHG emission values in the updated and previous versions of GREET 2. Finally, results from a sensitivity analysis are presented for identifying life cycle parameters that most affect vehicle life cycle estimates.     

Herbage intake,methane emissions and animal performance of steers grazing dwarf elephant grass v. dwarf elephant grass and peanut pastures

Management strategies for increasing ruminant legume consumption and mitigating methane emissions from tropical livestock production systems require further study. The aim of this work was to evaluate the herbage intake, animal performance and enteric methane emissions of cattle grazing dwarf elephant grass (DEG) (Pennisetum purpureum cv. BRS Kurumi) alone or DEG with peanut (Arachis pintoi cv. Amarillo). The experimental treatments were the following: DEG pastures receiving nitrogen fertilization (150 kg N/ha as ammonium nitrate) and DEG intercropped with peanut plus an adjacent area of peanut that was accessible to grazing animals for 5 h/day (from 0700 to 1200 h). The animals grazing legume pastures showed greater average daily gain and herbage intake, and shorter morning and total grazing times. Daily methane emissions were greater from the animals grazing legume pastures, whereas methane emissions per unit of herbage intake did not differ between treatments. Allowing animals access to an exclusive area of legumes in a tropical grass-pasture-based system can improve animal performance without increasing methane production per kg of dry matter intake.     

Fluxes of CO2, CH4 and N2O from a Welsh peatland following simulation of water table draw-down: Potential feedback to climatic change

A potential effect of climatic change was simulated by manipulating the water table height within intact peat monoliths. The treatment decreased methane flux (maximum –80%) and increased both carbon dioxide flux (maximum 146%) and nitrous oxide flux maximum 936%). Returning the water table height to its original level caused both nitrous oxide and carbon dioxide flux to rapidly return to control levels. However, methane flux remained at its experimentally induced low levels.