Interactions of Carbon Cycling, Nitrogen Cycling, and Nitrogen (N) Stable Isotopes in Plants as Affected by Mycorrhizal Fungi, N Availabilty and N Form

摘要：氮的有效性经常限制林业和农业中的植物生长，而大气沉积中过量的氮对整个美国的森林造成越来越大的危害。菌根真菌是重要的植物共生体，通过吸收、保持和转移土壤中的氮素，直接影响植物的生长和氮素循环。因此，它们基本上没有出现在用于预测森林生长和胁迫反应的森林功能和生态系统模型的概念性图景中。叶片15N：14N比例是共生中碳和氮分配的有用标志，但我们对15N：14N分配的生化机制了解有限。我们将测量供应不同氮素形态、不同氮素有效性和不同真菌共生体的樟子松菌根幼苗的完整碳和氮同位素收支。光合作用、地下呼吸和地上呼吸也将被量化。我们还将使用质谱学和核磁共振测量的数据来研究导致15N：14N模式的潜在生化机制。通过这些培养实验，我们将准备(1)测量不同环境条件下生态系统中菌根真菌的碳分配，(2)使用叶片15N：14N测量来指示菌根真菌的分配，以及(3)明确地将菌根真菌纳入生态系统水平的模型。更广泛的影响：这项工作将提高对是什么调节森林生产力和在人为氮沉积下菌根共生功能的理解。将有至少3名研究生接受这笔助学金的培训。

ABSTRACT: Nitrogen (N) availability often limits plant growth in forestry and agriculture, while excess N in atmospheric deposition increasingly harms forests throughout the US. Mycorrhizal fungi are key plant symbionts and directly influence plant growth and N cycling through the uptake, retention, and transfer of soil-derived N. At present, mycorrhizal symbioses are poorly understood. Consequently, they are largely absent from conceptual pictures of forest functioning and ecosystem models used to predict forest growth and stress responses. Foliar 15N:14N ratios appear useful markers of carbon and N allocation in the symbiosis, but we have limited understanding of biochemical mechanisms regulating 15N:14N distributions. We will measure complete carbon and N isotope budgets in mycorrhizal Pinus sylvestris seedlings supplied with different N forms, at different N availabilities, and with different fungal symbionts. Photosynthesis, belowground respiration, and aboveground respiration will also be quantified. We will also investigate the underlying biochemical mechanisms causing 15N:14N patterns using data from mass spectrometry and nuclear magnetic resonance measurements. From these experiments in culture, we will be poised to (1) measure carbon allocation to mycorrhizal fungi in ecosystems under different environmental conditions, (2) use foliar 15N:14N measurements to indicate allocation to mycorrhizal fungi, and (3) explicitly incorporate mycorrhizal fungi into ecosystem-level models. BROADER IMPACTS: This work will improve understanding of what regulates forest productivity and the functioning of mycorrhizal symbioses under anthropogenic N deposition. There will be at least 3 graduate students trained on this grant.