Do Archaea dominate nitrification in acid soils?

在酸性土壤中，哪些生物负责氮素循环？硝化作用对整个环境中氮素的循环是必不可少的。它涉及两组微生物将氨转化为硝酸盐。氨氧化剂将氨转化为亚硝酸盐，亚硝酸盐氧化剂随后将亚硝酸盐转化为亚硝酸盐。尽管硝化作用是一个必要的过程，但它也可能产生有害的后果。铵可以保留在土壤中，但在转化为硝酸盐后，它很容易被淋溶，导致可用于供应饮用水的地下水受到污染。此外，氨氧化还伴随着一氧化二氮的产生，一氧化二氮是一种强有力的温室气体，也参与破坏大气中的平流层臭氧。世界上大约30%的土壤可以被认为是酸性的(PH值低于5.5)，代表了包括林业、农业和草原在内的广泛的自然和管理栖息地。因此，它们具有重要的环境和经济意义。与其他土壤(如受管理的耕地)不同，在酸性土壤中负责硝化作用的过程和生物还没有被完全了解，因为被认为主要负责氨氧化的典型氨氧化菌不能在酸性pH的实验室介质中生长。直到最近，人们还认为土壤中最重要的氨氧化菌是细菌。然而，随着最近发现的另一组具有氧化氨能力的丰富的有机体--新古菌，这种观点已经改变。这些生物属于微生物生命的另一个领域--古生菌。尽管它们在许多方面与细菌相似，但它们在进化上是截然不同的。这些生物曾被认为仅限于深海喷口或陆地温泉等极端嗜热环境中。然而，随着分子技术的使用，这些生物已经被证明在环境中无处不在。我们最近获得的证据表明，在一个试验田地点，氨氧化文氏菌在酸性土壤中显示出最大的活性，而氨氧化细菌在中性土壤中显示出最大的活性。因此，这表明这两个群体之间存在着根本的生态和生理差异。这项研究计划旨在确定在一系列不同生境的酸性土壤中，是否是土壤微生物而不是细菌对氨氧化负有主要责任。它们的丰度将在英国境内四个地点的酸性土壤和邻近的中性pH土壤中进行测量，它们的相对丰度也将在其他三个国家(芬兰、加拿大和澳大利亚)的森林和牧场土壤中进行测定。这些发现将使农业、林业和工业领域的人受益，因为我们增加了对自然和受管理的酸性土壤系统中负责氮循环的有机体的了解。对于试图了解生物多样性和生态系统功能之间的联系的研究人员来说，这些发现也将是重要的，包括可能导致土壤一氧化二氮排放的机制和生物。

Which organisms are responsible for nitrogen cycling in acid soils? Nitrification is essential to the cycling of nitrogen throughout the environment. It involves the conversion of ammonia to nitrate by two groups of microorganisms. Ammonia oxidisers convert ammonia to nitrite, which is subsequently converted to nitrite by nitrite oxidisers. Although an essential process, nitrification can also have deleterious consequences. Ammonium can be retained in soil, but after conversion to nitrate, it can be readily leached resulting in the pollution of groundwaters that may be used to supply drinking water. In addition, ammonia oxidation is accompanied by the production of nitrous oxide, a potent greenhouse gas which is also involved in destroying stratospheric ozone in the atmosphere. Approximately 30% of the world's soil can be considered acid (with a pH less than 5.5) and represent a wide range of natural and managed habitats including forestry, agriculture and grasslands. They are therefore of great environmental and economic importance. In contrast to other soils (such as managed arable land), the processes and organisms responsible for nitrification in acid soils are not fully understood, as typical ammonia oxidisers that were thought to be primarily responsible for ammonia oxidation are unable to grow in laboratory media at acidic pH. Until recently it was believed that the most important soil ammonia oxidisers were bacteria. However, this view has changed with the recent discovery of another group of abundant group of organisms that possess the ability to oxidise ammonia, the Crenarchaea. These organisms belong to another domain of microbial life, the archaea. Although they resemble bacteria in many ways, they are evolutionary distinct. These organisms were once thought to be restricted to hyperthermophilic environments such as deep-sea vents or terrestrial thermal springs. However, with the use of molecular techniques, these organisms have been demonstrated to be ubiquitous in the environment. We have recently obtained evidence that in one experimental field site, ammonia oxidising Crenarchaea show greatest activity in acidic soils, in direct contrast to ammonia oxidising bacteria which show greatest activity in neutral soils. This therefore indicates that there are fundamental ecological and physiological differences between these two groups. This research programme aims to determine whether soil crenarchaea, rather than bacteria, are primarily responsible for ammonia oxidation in acid soils from a range of different habitats. Their abundance will be measured in acidic soils and neighbouring neutral pH soils from four sites from within the UK, and their relative abundance will also be determined in forest and pasture soils from three other countries (Finland, Canada and Australia). The findings will benefit those in agriculture, forestry and industry by increasing our knowledge of the organisms responsible for nitrogen cycling in natural and managed acidic soil systems. The findings will also be important to researchers trying to understand the links between biodiversity and ecosystem function, including the mechanisms and organisms potentially responsible for the emission of nitrous oxide from soil.