Understanding nitrous oxide emission from denitrifying bacteria: integrating chemostat and soil studies

了解反硝化细菌的一氧化二氮排放：整合恒化器和土壤研究

• 批准号: BB/H013431/1
• 负责人: Liz Baggs
• 金额: $ 42.29万
• 依托单位: University of Aberdeen
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=BB%2FH013431%2F1
• 关键词: Understanding; nitrous; oxide; emission; denitrifying

We humans we are entirely dependent on the oxygen we breath to support our metabolic processes. Significantly, this is not so for many species of bacteria. Faced with a shortage of oxygen in their environment many bacterial species are able to switch to using nitrate (NO3-), rather than oxygen to support respiration. One of these energy yielding processes, known as denitrification, converts water-soluble nitrates to gaseous products, nitric oxide (NO), nitrous oxide (N2O) and dinitrogen (N2). This denitrification process can take place extensively in agricultural soils where nitrogen rich fertilisers added to stimulate plant growth can also stimulate bacterial nitrogen cycling. Soil bacteria which can denitrify need to protect themselves from the autotoxic effects of NO produced through their own metabolism. They have an enzyme, nitric oxide reductase (NOR) that has evolved to keep endogenous NO levels low by converting it to the relatively benign nitrous oxide (N2O) which can be released into the atmosphere. From the perspective of bacterial metabolism the job of detoxifying the cytoxic NO is done when it is converted to N2O, but from an environmental perspective an envirotoxin, a greenhouse gas, has been produced. When discussing greenhouse gas emissions the public are acutely aware of the problems posed by carbon dioxide and methane. However, emissions of N2O, perhaps best known as the dental anaesthetic 'laughing gas', should also cause concern. N2O was first discovered by the British chemist Joseph Priestley in 1793 when its atmospheric levels had been steady for millennia. However, over the last 100 years N2O in the atmosphere has increased by 50 parts per billion and this atmospheric loading is increasing further by 0.25% each year, with most commentators linking this increase to intensive use of fertiliser to increase farmland productivity in the 20th Century. Although its atmospheric levels are only a fraction of that of CO2 it has a 300-fold greater global warming potential. Thus when expressed in terms of CO2 equivalents it represents around 10% of total global emissions of greenhouse gases. Since it has an atmospheric lifetime of some 150 years the N2O produced today will potentially influence the climate experienced by our great-great grandchildren thus it is important to devise strategies to mitigate these releases now. The pathways by which denitrifying bacteria produce NO from nitrate are undertstood from a molecular level with structures of enzymes that convert nitrate to nitrite (nitrate reductases) and nitrite to nitric oxide (nitrite reductases) being known. These enzymes are metalloproteins that depend on transition metals such as molybdenum, iron and copper for activity. The enzyme that breaks down N2O to inert N2 is a copper-containing enzyme (Nos). It is the major enzyme on the planet that is responsible for the potent N2O greenhouse gas. Without it the atmospheric levels of N2O would be much greater that they currently are. The molecular structure of Nos is known. It contains twelve atoms of copper and so its activity in the environment is dependent on the bioavailability of copper. It is also sensitive to pH and oxygen and so its activity in the environment is dependent on a number of different environmental variables. The largest source of anthropogenic N2O emissions is agricultural soils because of the application of nitrogenous fertilisers to soils. Since the UK signed up to the Kyoto Protocol, many non-biological sources of N2O emissions have been reduced, but emissions from biological sources are less easy to manage. Efforts to improve the prediction and management of agricultural N2O emissions will benefit from a better understanding of the factors that influence the net production of N2O by bacteria. This requires a combination of studies on model organisms in controlled laboratory environments and on studies in situ in soils. This project will provide such an a integrated study.

我们人类完全依赖我们呼吸的氧气来支持我们的新陈代谢过程。值得注意的是，对于许多种类的细菌来说，情况并非如此。面对环境中氧气的短缺，许多细菌物种能够改用硝酸盐(NO3-)，而不是氧气来支持呼吸。其中一个产生能量的过程被称为反硝化，它将水溶性硝酸盐转化为气态产物，即一氧化氮(NO)、一氧化二氮(N2O)和氮气(N2)。这种反硝化过程可以在农业土壤中广泛发生，在那里添加富氮化肥来刺激植物生长也可以刺激细菌的氮循环。能够反硝化的土壤细菌需要保护自己免受通过自身新陈代谢产生的一氧化氮的自毒效应。它们有一种酶，一氧化氮还原酶(NOR)，通过将其转化为相对无害的一氧化二氮(N2O)，使内源性NO水平保持在较低水平，从而可以释放到大气中。从细菌代谢的角度来看，当有毒的NO转化为N2O时，解毒工作就完成了，但从环境角度来看，已经产生了一种环境毒素，一种温室气体。在讨论温室气体排放时，公众敏锐地意识到二氧化碳和甲烷带来的问题。然而，N2O的排放也应该引起人们的关注。N2O可能最为人所知的是牙科麻醉剂“笑气”。N2O是由英国化学家约瑟夫·普里斯特利于1793年首次发现的，当时它的大气水平几千年来一直保持稳定。然而，在过去的100年里，大气中的N2O增加了百万分之50，而且这种大气负荷每年还在以0.25%的速度进一步增加，大多数评论人士将这种增加与20世纪密集使用化肥以提高农田生产力联系在一起。尽管它的大气水平只有二氧化碳的一小部分，但它的全球变暖潜力是二氧化碳的300倍。因此，当用二氧化碳当量表示时，它约占全球温室气体排放总量的10%。由于它的大气寿命约为150年，今天产生的N2O可能会影响我们的曾孙所经历的气候，因此，现在就制定战略来缓解这些排放是很重要的。反硝化细菌从硝酸盐产生NO的途径从分子水平上被理解，将硝酸盐转化为亚硝酸盐(硝酸盐还原酶)和亚硝酸盐转化为一氧化氮(亚硝酸盐还原酶)的酶的结构是已知的。这些酶是金属蛋白，依赖于钼、铁和铜等过渡金属的活性。将N2O分解成惰性氮气的酶是一种含铜的酶(NOS)。它是地球上主要的酶，负责产生强有力的N2O温室气体。如果没有它，大气中的N2O水平将比目前高得多。一氧化氮合酶的分子结构是已知的。它含有12个铜原子，因此它在环境中的活动取决于铜的生物有效性。它对pH和氧气也很敏感，因此它在环境中的活性取决于许多不同的环境变量。人为N2O排放的最大来源是农业土壤，因为氮肥在土壤中的应用。自从英国签署《京都议定书》以来，许多非生物来源的N2O排放已经减少，但生物来源的排放不那么容易管理。更好地了解影响细菌净产生N2O的因素，将有助于改进对农业N2O排放的预测和管理。这需要在受控的实验室环境中对模型生物进行研究和在土壤中进行现场研究相结合。该项目将提供这样一项综合研究。

项目成果

Combined effects of rhizodeposit C and crop residues on SOM priming, residue mineralization and N supply in soil

• DOI: 10.1016/j.soilbio.2017.05.026
• 发表时间: 2017-10
• 期刊: Soil Biology & Biochemistry
• 影响因子: 9.7
• 作者: Lumbani Mwafulirwa;E. Baggs;J. Russell;N. Morley;A. Sim;E. Paterson

Compound driven differences in N2 and N2O emission from soil; the role of substrate use efficiency and the microbial community

• DOI: 10.1016/j.soilbio.2016.11.028
• 发表时间: 2017-03-01
• 期刊: SOIL BIOLOGY & BIOCHEMISTRY
• 影响因子: 9.7
• 作者: Giles, Madeline E.;Daniell, Tim J.;Baggs, Elizabeth M.
• 通讯作者: Baggs, Elizabeth M.

Nitrous oxide emissions from soils: how well do we understand the processes and their controls?

• DOI: 10.1098/rstb.2013.0122
• 发表时间: 2013-07-05
• 期刊: Philosophical transactions of the Royal Society of London. Series B, Biological sciences
• 作者: Butterbach-Bahl K;Baggs EM;Dannenmann M;Kiese R;Zechmeister-Boltenstern S
• 通讯作者: Zechmeister-Boltenstern S

Nitrogen availability alters rhizosphere processes mediating soil organic matter mineralisation

• DOI: 10.1007/s11104-017-3275-0
• 发表时间: 2017-05
• 期刊: Plant and Soil
• 影响因子: 4.9
• 作者: Conor J. Murphy;E. Baggs;N. Morley;D. Wall;E. Paterson