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Ectomycorrhizal Fungi and the Enzymatic Liberation of Nitrogen from Soil Organic Matter: Ecosystem Processes and Underlying Molecular Mechanisms

外生菌根真菌和土壤有机质中氮的酶解释放：生态系统过程和潜在分子机制

基本信息

批准号：
1754369
负责人：
Donald Zak
金额：
$ 89.89万
依托单位：
Regents of the University of Michigan - Ann Arbor
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2018
资助国家：
美国
起止时间：
2018-07-01 至 2022-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1754369&HistoricalAwards=false
关键词：
Ectomycorrhizal Fungi Enzymatic Liberation Nitrogen

项目摘要

The rate at which plants can photosynthesize, thereby capturing carbon from the atmosphere, is limited by a number of factors including the availability of nitrogen (N) in soil. A century of research has presumed that forest trees can exclusively use inorganic nitrogen (i.e., ammonium and nitrate) to fuel their growth. However, recent work has suggested that plants may have access to additional types of nitrogen in the form of more complex organic molecules (organic N) also present in the soil. The key to this story is that nearly all forest trees form symbiotic relationships with fungi that dwell on plant roots below ground. These fungi act to extend the root system of plants and increase plant access to limiting nutrients, including organic N. This research will explore the capacity for certain groups of fungi to provide forest trees with organic forms of nitrogen. More specifically, this work will explore the unknown capacity of such fungi to decompose soil organic matter using enzymes, thereby releasing organic N in soil organic matter for plant uptake. The broad goal of this research project, then is to understand the extent which these root-associated fungi are liberating organic N in soil for use by trees. This project will also provide K-12 teachers with age-appropriate teaching tools to build students' understanding of forest ecology. Recent global level modeling efforts indicate that trees that associate with ectomycorrhizal fungi mutualists will be fertilized by increasing concentrations of atmospheric CO2. Other evidence suggests that the large stocks of C in forest soils are a result of the enzymatic activity of ectomycorrhizal (ECM) fungi. Both models rest upon the hereto untested general claim that ECM fungi mobilize N from the large pools of soil organic matter (SOM). However, direct evidence that ECM fungi can function in this manner is lacking. Understanding the extent to which these organisms obtain organic N by degrading SOM is contingent on whether genes encoding enzymes that mediate both the decay of plant detritus and SOM, were retained during their evolutionary history and are deployed when in symbiosis with plant roots. Multiple lines of indirect evidence, stemming from whole genome sequencing and field data indicate that only certain evolutionary lineages of ECM fungi have the potential to provision their plant hosts with N that is obtained from SOM. Resolving the saprotrophic physiology of ECM fungi across a range of spatial scales and soil N conditions, holds promise to resolve the ecological forces governing where we may expect plants to commonly obtain growth-limiting N from SOM via the activity of their ECM mutualists. Accordingly, this project will use a synthetic whole-plant system to measure the enzymatic expression of genes encoding lignocellulolytic enzymes across a wide phylogenetic range of ECM fungi, and will also trace organic N into intact plants. After validating this mechanism in the laboratory, the occurrence of this phenomenon will be tested using meta-transcriptomic enabled field approaches. Overall, the research will span gradients in soil N availability occurring at both the local and ecosystem level scales to improve understanding of the factors that structure the distribution of ECM fungi that obtain N from SOM.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

植物光合作用的速率，从而从大气中捕获碳，受到许多因素的限制，包括土壤中氮（N）的可用性。一个世纪的研究已经假定林木可以专门利用无机氮（即，铵和硝酸盐）来促进它们的生长。然而，最近的研究表明，植物可能以更复杂的有机分子（有机氮）的形式获得其他类型的氮，这些分子也存在于土壤中。这个故事的关键是，几乎所有的森林树木都与居住在地下植物根部的真菌形成共生关系。这些真菌的作用是延长植物的根系，增加植物对有限养分的吸收，包括有机氮。这项研究将探索某些真菌群为森林树木提供有机形式氮的能力。更具体地说，这项工作将探索这种真菌使用酶分解土壤有机质的未知能力，从而释放土壤有机质中的有机氮供植物吸收。本研究项目的主要目标是了解这些根相关真菌释放土壤中有机氮供树木使用的程度。该项目还将为K-12教师提供适合年龄的教学工具，以建立学生对森林生态的理解。最近的全球水平的建模工作表明，树木与外生菌根真菌互利共生将通过增加大气CO2浓度施肥。其他证据表明，森林土壤中的大量碳是外生菌根（ECM）真菌的酶活性的结果。这两种模型都基于迄今为止未经检验的一般性主张，即ECM真菌从土壤有机质（SOM）的大池中动员N。然而，ECM真菌可以以这种方式发挥作用的直接证据缺乏。了解这些生物通过降解SOM获得有机氮的程度取决于编码介导植物碎屑和SOM腐烂的酶的基因是否在其进化历史中被保留，并且在与植物根共生时被部署。来自全基因组测序和现场数据的多条间接证据表明，只有某些进化谱系的ECM真菌有潜力提供其植物宿主与N，是从SOM。解决腐营养生理的ECM真菌在一系列的空间尺度和土壤氮的条件下，有望解决的生态力量，我们可以期望植物通常获得限制生长的N从SOM通过他们的ECM互惠的活动。因此，该项目将使用合成的全植物系统来测量编码木质纤维素分解酶的基因在ECM真菌的广泛系统发育范围内的酶表达，并且还将追踪有机N到完整的植物中。在实验室中验证这种机制后，将使用元转录组学启用的场方法来测试这种现象的发生。总体而言，研究将跨越梯度土壤氮的可用性发生在当地和生态系统水平的尺度，以提高结构的ECM真菌，从SOM获得N的分布的因素的理解。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用该基金会的智力价值和更广泛的影响审查标准进行评估的支持。