The Fate of Methanotrophically Fixed Carbon in Terrestrial Environments

气候变化的主要原因是通过燃烧化石燃料将埋藏在地下数百万年的大量碳重新排放到大气中。一旦回到大气中，含碳化合物就会吸收红外线辐射，从而导致全球变暖。限制全球变暖影响的一个有效方法是去除大气中的含碳化合物，如二氧化碳（CO2）和甲烷（CH4）。大气中碳的去除及其在陆地环境（如土壤）中的储存被称为碳固存。有许多固碳的自然过程，包括陆地植被和海洋生物去除大气中的二氧化碳。甲烷中的碳也可以像二氧化碳中的碳一样被隔离。甲烷氧化菌是一种可以利用甲烷作为唯一碳源的细菌，是陆地上主要的甲烷汇。甲烷营养细菌可以去除大部分在陆地环境中形成的甲烷，并阻止其进入大气。在这种情况下，它们形成了一个重要的屏障，阻止天然湿地、稻田、海洋沉积物和垃圾填埋场释放甲烷。虽然土壤中甲烷氧化菌氧化的甲烷量已被广泛研究，但人们对土壤中甲烷中碳的命运以及这些碳中有多少被封存知之甚少。为了弄清楚土壤中甲烷氧化后碳会发生什么变化，我们将把含有示踪剂的CH4 （13c标记的甲烷）应用到一系列不同的土壤中。然后，我们将跟踪标签在土壤中的命运，以计算CH4中的碳在土壤中保留的比例。我们还可以将13c标记的CH4与其他利用甲烷中的碳作为食物来源的土壤微生物联系起来，并建立一个更广泛的土壤微生物食物网的图片。本研究将研究三种不同的土壤环境。初期的开发工作将研究垃圾填埋场覆盖土壤，并重点建立一系列新的分析技术。垃圾填埋场上覆盖的土壤含有高浓度的甲烷，因为垃圾填埋场的有机废物降解时，会释放出大量甲烷。甲烷通过覆盖场地的土壤渗透到大气中。众所周知，垃圾填埋场覆盖土壤中的细菌氧化了大部分甲烷，但它们消耗这些碳的最终命运尚不清楚。自然湿地中甲烷碳的命运也将被研究。天然湿地包括泥炭沼泽、沼泽、盐沼和热带沼泽等环境。天然湿地有丰富的有机土壤，当土壤有机质降解时，它们释放甲烷的方式与垃圾填埋场相似。我们将研究甲烷中的碳在被土壤中的甲烷营养细菌消耗后的命运。最后一种将用于评估土壤中甲烷碳的去向的土壤类型是一系列土壤时间序列。土壤年表是在相似的植被、地形和气候条件下形成的一组相关的土壤。土壤发育的时间长短是土壤在时间顺序上的唯一区别。这将使我们能够评估土壤发育与涉及碳固存的土壤过程之间的关系。总的来说，这项研究将增加我们对碳的命运的理解，因为它是主要的温室气体之一，因为它被土壤微生物群落利用和分散。

The major cause of climate change is the atmospheric reintroduction via fossil fuel burning of large amounts of carbon that has been buried underground for millions of years. Once back in the atmosphere, the carbon-containing compounds absorb infrared radiation, which contributes to global warming. An effective way to limit the effects of global warming is through the removal of carbon containing compounds, such as carbon dioxide (CO2) and methane (CH4) from the atmosphere. The removal of atmospheric carbon and its storage in terrestrial environments, such as soils, is known as carbon sequestration. There are many natural processes that sequester carbon including the removal of atmospheric CO2 by terrestrial vegetation and marine organisms. Carbon from methane can also be sequestered in a similar way to carbon from CO2. Methanotrophs are bacteria that can utilise methane as their only source of carbon and are the major terrestrial methane sink. Methanotrophic bacteria remove a large proportion of methane formed in terrestrial environments and prevent it from reaching the atmosphere. In these circumstances they form a vital barrier that prevents the release of methane from natural wetlands, rice paddies, marine sediments and landfill sites. Whilst the amount of methane oxidised by methanotrophs in soils has been widely studied little is known about the fate of carbon from methane in soils and how much of this carbon is sequestered. To work out what happens to the carbon following methane oxidation in soils we are going to apply CH4 containing a tracer (13C-labelled methane) to a range of different soils. We will then track the fate of the label in the soil, to calculate what proportion of the carbon from CH4 is retained in the soil. We can also link the 13C-labelled CH4 to other soil microorganisms that utilise the carbon from methane as a source of food, and build up a picture of the wider soil microbial food web. Three different soil environments are going to be studied in this work. The initial development work will study a landfill cover soil and focus on establishing a range of new analytical techniques. The soil that overlays a landfill site contains extremely high concentrations of methane because as the organic waste in the landfill site degrades, it releases large amounts of methane. The methane permeates out to the atmosphere through the soil that covers the site. It is well known that bacteria in the landfill cover soils oxidise a large proportion of this methane but the ultimate fate of this carbon they consume is unknown. The fate of methane carbon in natural wetlands will also be studied. Natural wetlands include environments such as peat bogs, fens, salt marshes and tropical swamps. Natural wetlands have organic rich soils that release methane in a similar way to landfill sites when the soil organic matter degrades. We are going to study the fate of carbon from this methane following consumption by methanotrophic bacteria in the soil. The final type of soils that will be used to assess the fate of carbon from methane in soils are a range of soil chronosequences. A soil chronosequence is a related set of soils that formed under similar conditions of vegetation, topography and climate. The length of time over which the soils have developed is the only difference between the soils in the chronosequence. This will allow us to assess the relationship between soil development and the soil processes involved in carbon sequestration. Overall, the research will add a new dimension our understanding of the fate of carbon from one of the major green house gases as it is utilised and dispersed by the soil microbial community.