Collaborative Research: Most Arctic Plants Obtain Nitrogen by Symbiosis with Fungi: Development of a Radical Concept Cooperative Project

P.I.：John Hobbie提案编号：0612595P.I.：Erik Hobbie提案编号：0612598北极植物受到有效氮(N)水平低的强烈限制，但土壤中的有机氮含量丰富。为了帮助获得氮和其他营养物质，木本植物与菌根真菌形成共生关系。在这种共生中，真菌从土壤氮库中获得无机和有机氮，并将有机氮化合物转移到植物中，同时从植物中获得糖。到目前为止，对这些途径的研究要么是定性的，要么是依赖于人为高浓度的添加同位素N-有机化合物，这使得对自然生态系统的推断变得困难。现在，在阿拉斯加图利克湖的苔原上进行的一项新研究使用自然水平的同位素N来量化共生提供给植物的N的数量，以及从植物转移到真菌的碳的数量。第二种新方法通过对蛋白质和结构碳的天然放射性碳测量，直接确定植物和真菌组织中土壤来源的有机氮的存在。对北极碳和氮循环的研究的影响包括：1)为了了解当前的氮循环并预测未来气候下的氮循环，需要有关什么控制菌根生长以及这些真菌是否可以获取锁定在土壤有机质中的氮的信息；2)必须修改泛北极碳循环模型，以包括植物菌根生长的能源成本以及菌根真菌向木本植物提供的氮。拟议活动产生的更广泛影响包括对研究生和本科生的培训。巴罗(主要是爱斯基摩因努皮亚特人)的K-12学生将了解该项目，并通过巴罗校园计划帮助收集蘑菇和植物，该计划部分由北极LTER项目资助。该研究项目将在一个本科院校和两个研究机构之间建立合作伙伴关系。研究结果可能会带来一种范式转变--森林和生态系统科学家现在必须考虑菌根共生体及其在从土壤向灌木和树木提供有机氮方面的作用。研究重点将重新放在研究真菌攻击土壤有机质的能力上。必须对二氧化碳浓度增加和气候变暖对地下N循环和真菌共生体分配的影响进行新的测量。由于这项研究将提供评估C分配给菌根真菌和生态系统中有机N吸收的重要性的方法，因此它将促进将这些重要过程纳入用于管理的生态系统C和N模型。

P.I.: John Hobbie Proposal Number: 0612595P.I.: Erik Hobbie Proposal Number: 0612598Arctic plants are strongly limited by low levels of available nitrogen (N) yet organic N in the soil is abundant. To aid in obtaining nitrogen and other nutrients, woody plants form symbioses with mycorrhizal fungi. In this symbiosis, fungi obtain inorganic and organic N from soil N pools and transfer organic N compounds to plants while obtaining sugars from plants. Research into these pathways until now was either qualitative or relied on added isotopic N-organic compounds at artificially high concentrations, making extrapolation to natural ecosystems difficult. Now, new research in tussock tundra at Toolik Lake, Alaska uses natural levels of isotopic N to quantify the amount of N supplied to plants by the symbiosis as well as the amount of carbon moving from the plants to fungi. A second new method determines directly the presence of soil-derived organic N in plant and fungal tissues by natural radiocarbon measurements on protein vs. structural C. Implications for Arctic research on C and N cycling include the following: 1) to understand current N cycling and predict N cycling under future climates, information is needed on what controls mycorrhizal growth and whether these fungi can access nitrogen locked in soil organic matter; 2) models of pan-Arctic carbon cycling must be modified to include the energy cost to plants of mycorrhizal growth and the accompanying supply of nitrogen to woody plants by mycorrhizal fungi. Broader impacts resulting from the proposed activity include training of graduate and undergraduate students. K-12 students at Barrow (predominately Inupiat Eskimo) will learn about the project and assist in collecting mushrooms and plants through the Barrow Schoolyard program, funded in part by the Arctic LTER project. This research project will set up a partnership between an undergraduate institution and two research institutions. The research findings may create a paradigm shift -- forest and ecosystem scientists must now take into consideration the mycorrhizal symbionts and their role in supplying organic nitrogen from soil to shrubs and trees. Research emphasis will refocus to study the fungal abilities to attack soil organic matter. New measurements must be made of the effects of increased CO2 concentrations and a warming climate on below-ground N cycling and allocation to fungal symbionts. Because this study will provide methods to assess the importance of both C allocation to mycorrhizal fungi and organic N uptake in ecosystems, it will facilitate the inclusion of these important processes in ecosystem C and N models used for management.