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

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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.