15N foliar dilution of lodgepole pine: from where does the atmospheric N originate

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Soil microorganisms are integral components of forest ecosystems, fulfilling critical roles in nutrient cycling, maintenance of soil structure, and regulation of plant growth. A process even as central to forest growth as nitrogen cycling has yet to be fully elucidated, notwithstanding the vital role it plays in forests worldwide. For example, lodgepole pine is a widely distributed species known to grow under a variety of soil conditions. Its ability to grow on nutrient-poor, coarse-textured soils is unique for a species not known to fix nitrogen, and poses interesting questions regarding its nitrogen source in such environments. I propose to determine if nitrogen fixing bacteria are capable of fixing nitrogen while living inside pine mycorrhiza, root, stem and needle tissues using biomarkers to visualize bacteria as well as nif gene expression in situ.