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：0612595 P.I.：Erik Hobbie提案编号：0612598北极植物受到低水平有效氮（N）的强烈限制，但土壤中的有机氮丰富。为了帮助获得氮和其他养分，木本植物与菌根真菌形成共生。在这种共生关系中，真菌从土壤氮库中获得无机氮和有机氮，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，要么依赖于人为高浓度的同位素N-有机化合物，使外推到自然生态系统变得困难。现在，在阿拉斯加图里克湖的草丛苔原中进行的新研究使用自然水平的同位素N来量化共生体提供给植物的N量以及从植物转移到真菌的碳量。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。对北极碳氮循环研究的启示包括：1）了解当前的氮循环和预测未来气候条件下的氮循环，需要了解控制菌根生长的因素以及这些真菌能否获得土壤有机质中的氮; 2）泛-北极的碳循环必须加以修改，以包括能源成本的植物菌根生长和伴随供应的氮木本植物的菌根真菌。拟议活动产生的更广泛影响包括培训研究生和本科生。K-12学生在巴罗（主要是Inupiat爱斯基摩人）将了解该项目，并协助收集蘑菇和植物通过巴罗校园计划，部分资金由北极LTER项目。本研究项目将建立一个本科院校和两个研究机构之间的伙伴关系。研究结果可能会产生一个范式转变-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。研究重点将重新集中在真菌对土壤有机质的侵蚀能力上。必须进行新的测量的影响，增加CO2浓度和气候变暖的地下N循环和分配真菌共生体。因为这项研究将提供方法来评估碳分配给菌根真菌和生态系统中的有机氮吸收的重要性，它将促进包括这些重要的过程中的生态系统C和N模型用于管理。

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.