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（N）的可用性往往限制了林业和农业中的植物生长，而大气沉积中过量的N越来越多地危害美国各地的森林。 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。 目前，对菌根共生关系的了解还很少。 因此，在森林功能的概念图和用于预测森林生长和压力反应的生态系统模型中，基本上没有这些概念。 叶片15 N：14 N比值是共生关系中碳氮分配的有用指标，但对15 N：14 N分配的生化调控机制了解有限。我们将测量完整的碳和氮同位素预算菌根樟子松幼苗提供不同的N形式，在不同的N有效性，并与不同的真菌共生体。 光合作用，地下呼吸，地上呼吸也将被量化。 我们还将使用质谱和核磁共振测量的数据研究导致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）在不同环境条件下测量生态系统中菌根真菌的碳分配，（2）使用叶片15 N：14 N测量来指示菌根真菌的分配，（3）明确将菌根真菌纳入生态系统水平的模型。 更广泛的影响：这项工作将提高了解是什么调节森林生产力和菌根共生体的人为氮沉降下的功能。 将有至少3名研究生接受这项赠款的培训。

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.