Assessing the Contribution of Nitrogen from Soil Organic Matter on Plant Growth Response to Elevated Carbon Dioxide

森林有能力通过吸收大气中的二氧化碳并将其储存在植物组织中来减缓全球变暖。然而，植物对二氧化碳的吸收是由其他资源的可用性控制的，如氮，这是光合作用中必不可少的元素。由于大多数森林的氮供应有限，树木可能无法达到其最大的碳吸收潜力。该项目研究了一种新的机制，通过这种机制，树木可以获得土壤中额外的氮源，从而使它们能够吸收更多的碳。其机制涉及外生菌根真菌、树木根系和森林土壤之间的关系。了解这一机制是如何工作的，它发生在景观中的哪里，以及哪些树木受益最大，可以更好地预测森林碳储量。这一信息有助于更准确地量化森林减缓气候变化的潜力，并将指导更好地管理这些系统。该项目培训了几名本科生和研究生，从而为STEM劳动力做出贡献。该项目还包括与密歇根州的部落合作伙伴合作，模拟不同情景下的景观森林动态。该项目评估树木如何利用外生菌根真菌潜在地获取土壤有机质中的氮。此外，该项目还评估了获得额外的氮如何提高净初级生产力，特别是在大气二氧化碳浓度升高的情况下。外生菌根真菌提高树木生产力的假设以前没有在野外条件下进行过测试。本工作通过田间试验沿沿着氮素梯度直接探讨了这一机制。两个硬木树种生长沿着这一梯度-红枫和红橡树-将进行研究。该项目还利用贝叶斯模型的结果来提高陆地生物地球化学模型的准确性。这项研究发现：1）有机氮有助于植物营养的条件; 2）对树木生长的贡献的大小;以及3）在大气二氧化碳浓度升高的情况下有机氮对树木生产力的影响。该项目定义了外生菌根真菌为树木提供土壤有机质中氮的条件。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Forests have the capacity to mitigate global warming by absorbing carbon dioxide from the atmosphere and storing it in plant tissues. However, plant uptake of carbon dioxide is controlled by the availability of other resources, like nitrogen, an element essential in photosynthesis. Because the supply of nitrogen is limited in most forests, trees could be prevented from reaching their maximum carbon uptake potential. This project investigates a new mechanism by which trees may access additional sources of nitrogen in the soils, and therefore enable them to absorb more carbon. The mechanism involves relationships among ectomycorrhizal fungi, tree roots, and forest soils. Understanding how this mechanism works, where it takes place in the landscape, and which trees benefit most, enables better predictions of forest carbon storage. This information allows more accurate quantification of the climate mitigation potential of forests and will guide better management of these systems. This project trains several undergraduate and graduate students, thereby contributing to the STEM workforce. This project also includes collaboration with tribal partners in Michigan to model landscape forest dynamics under different scenarios.This project evaluates how trees potentially access nitrogen that is bound in soil organic matter using ectomycorrhizal fungi. Further, the project assesses how access to this additional nitrogen could increase net primary productivity, especially under elevated atmospheric carbon dioxide concentrations. The assumption that ectomycorrhizal fungi increase tree productivity has previously been untested under field conditions. This work directly investigates this mechanism through a field experiment along a nitrogen gradient. Two hardwood tree species that grow along this gradient- red maple and red oak- will be studied. The project also uses results from Bayesian models to improve the accuracy of terrestrial biogeochemical models. This research discovers: 1) the conditions under which organic nitrogen contributes to plant nutrition; 2) the magnitude of that contribution to tree growth; and 3) the effect of organic nitrogen on tree productivity under elevated atmospheric carbon dioxide concentrations. This project defines the conditions under which ectomycorrhizal fungi provide trees with nitrogen bound in soil organic matter.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.