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The mycorrhizal hyphosphere: a key driver of biogeochemical cycles?

菌根菌丝圈：生物地球化学循环的关键驱动因素？

基本信息

批准号：
BB/E014879/1
负责人：
Angela Hodge
金额：
$ 34.92万
依托单位：
University of York
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2007
资助国家：
英国
起止时间：
2007 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=BB%2FE014879%2F1
关键词：
mycorrhizal hyphosphere key driver biogeochemical

项目摘要

Atmospheric carbon dioxide (CO2) levels have been rising steadily since the Industrial Revolution mainly as a consequence of human activity. Increased CO2 levels result in more heat absorbed from the sun thus contributing to global warming or 'the greenhouse effect'. This in turn has serious consequences for life on earth with loss of biodiversity, melting glaciers, forest fires and fatal heat waves. One of the major causes of increased CO2 levels is the burning of fossil fuels rapidly releasing carbon that has been stored for centuries back into the atmosphere. In order to cut our use of fossil fuels we can grow crops for energy. The large-scale production of such crops will dramatically alter the agricultural landscape. Energy (or 'biomass') crops are 'carbon neutral'; when burned to generate electricity they only release the same amount of CO2 back into the atmosphere as they fixed. Thus no 'extra' CO2 is released into the atmosphere. Energy crops include tree species such as Willow and Poplar. The roots of these plant species form symbiotic associations with mycorrhizal fungi naturally present in the soil and the term mycorrhizal literally means 'fungus-root'. Of the seven different types of mycorrhizal associations the two most important types are the ectomycorrhizal (ECM) which forms on tree species, and the arbuscular mycorrhizal association (AM), which forms mainly with herbaceous species. While most plants only form one type of association, both Willow and Poplar are unusual in that they can form both ectomycorrhizal or arbuscular mycorrhizal associations. Associations with mycorrhizal fungi can have direct benefits to the plant through increased growth, enhanced nutrient capture and disease suppression. In return, the mycorrhizal fungus obtains a supply of carbon from the host plant which helps it grow and produce an extensive mycelium external to the root. Plants influence the soil immediately surrounding their roots (called the 'rhizosphere') due to the presence of the growing root and as a result of compounds released from the root into the soil. Most of these compounds lost from the root through a passive process called 'exudation', are of low molecular weight and include amino acids, simple sugars and organic acids. These compounds are an ideal substrate for the microbial community; hence microbial populations are always higher in the rhizosphere compared to the bulk soil (i.e. soil not containing roots). Colonisation of roots by mycorrhizal fungi modifies the quantity and quality of compounds released from the roots but it is unknown to what extent the fungus actually contribute to the amount and types of compounds released. Moreover, in mycorrhizal plants, the external phase of the fungus (rather than the root) is the main zone of contact with the soil thus exudation of compounds from the hyphae may also influence microbial activities in the 'hyphosphere'. There is some evidence that ECM fungi can exude simple compounds but much less information on AM fungi although they are believed to improve soil structure by release of compounds from their hyphae. Thus, in this study we will examine to what extent ECM and AM fungi influence their surrounding environment. We will determine how much carbon flows to the fungus from the plant by using the carbon isotopes 14C (which is a radioactive isotope but very sensitive and from which we can obtain images of 14C flow through the plant to the fungus) and 13C (a stable hence non harmful isotope of C). We will also determine what types of compounds are exuded from the fungi by chemical analysis and by using biosensor microorganisms which can report back (via light omission) on the compounds released and the sites of release along the hyphae using a new approach called nanoSIMS. The influence of this hyphal exudation on a key soil process, denitrification, which results in a loss of N and which is also of environmental as well as economic concern will be quantified.

自工业革命以来，大气二氧化碳（CO2）水平一直在稳步上升，这主要是人类活动的结果。二氧化碳含量增加会导致从太阳吸收更多热量，从而导致全球变暖或“温室效应”。这反过来又对地球上的生命造成严重后果，包括生物多样性丧失、冰川融化、森林火灾和致命的热浪。二氧化碳含量增加的主要原因之一是化石燃料的燃烧迅速将储存了几个世纪的碳释放回大气中。为了减少对化石燃料的使用，我们可以种植农作物来获取能源。此类作物的大规模生产将极大地改变农业景观。能源（或“生物质”）作物是“碳中和”的；当燃烧发电时，它们只会将与固定数量相同数量的二氧化碳释放回大气中。因此，没有“额外”的二氧化碳被释放到大气中。能源作物包括柳树和杨树等树种。这些植物物种的根与土壤中自然存在的菌根真菌形成共生关系，菌根一词的字面意思是“真菌根”。在七种不同类型的菌根群中，最重要的两种类型是在树种上形成的外生菌根（ECM）和主要与草本物种形成的丛枝菌根群（AM）。虽然大多数植物只形成一种类型的群生，但柳树和杨树的不同寻常之处在于它们可以形成外生菌根或丛枝菌根群生。与菌根真菌的结合可以通过促进生长、增强养分捕获和抑制疾病对植物产生直接益处。作为回报，菌根真菌从宿主植物获得碳供应，帮助其生长并在根部外部产生广泛的菌丝体。由于正在生长的根的存在以及从根释放到土壤中的化合物，植物会影响其根周围的土壤（称为“根际”）。大多数这些化合物通过称为“渗出”的被动过程从根部流失，分子量较低，包括氨基酸、单糖和有机酸。这些化合物是微生物群落的理想底物；因此，与大块土壤（即不含根的土壤）相比，根际的微生物种群总是较高。菌根真菌在根部的定植改变了从根部释放的化合物的数量和质量，但尚不清楚真菌实际上对释放的化合物的数量和类型有多大贡献。此外，在菌根植物中，真菌的外相（而不是根）是与土壤接触的主要区域，因此菌丝中化合物的渗出也可能影响“菌丝圈”中的微生物活动。有一些证据表明 ECM 真菌可以分泌简单的化合物，但有关 AM 真菌的信息要少得多，尽管人们相信它们可以通过从菌丝中释放化合物来改善土壤结构。因此，在这项研究中，我们将研究 ECM 和 AM 真菌对其周围环境的影响程度。我们将使用碳同位素 14C（这是一种放射性同位素，但非常敏感，从中我们可以获得 14C 流经植物到真菌的图像）和 13C（一种稳定且无害的 C 同位素）来确定有多少碳从植物流向真菌。我们还将通过化学分析和使用生物传感器微生物来确定从真菌中渗出的化合物类型，生物传感器微生物可以使用一种称为 nanoSIMS 的新方法报告（通过光忽略）释放的化合物以及沿着菌丝的释放位点。这种菌丝渗出对关键土壤过程反硝化的影响将被量化，反硝化会导致氮的损失，同时也会引起环境和经济问题。