P.I.: John Hobbie Proposal Number: 0612595 P.I.: Erik Hobbie Proposal Number: 0612598
Arctic plants are strongly limited by low levels of available nitrogen (N) yet organic N in the soil is abundant. To aid in obtaining nitrogen and other nutrients, woody plants form symbioses with mycorrhizal fungi. In this symbiosis, fungi obtain inorganic and organic N from soil N pools and transfer organic N compounds to plants while obtaining sugars from plants. Research into these pathways until now was either qualitative or relied on added isotopic N-organic compounds at artificially high concentrations, making extrapolation to natural ecosystems difficult. Now, new research in tussock tundra at Toolik Lake, Alaska uses natural levels of isotopic N to quantify the amount of N supplied to plants by the symbiosis as well as the amount of carbon moving from the plants to fungi. A second new method determines directly the presence of soil-derived organic N in plant and fungal tissues by natural radiocarbon measurements on protein vs. structural C. Implications for Arctic research on C and N cycling include the following: 1) to understand current N cycling and predict N cycling under future climates, information is needed on what controls mycorrhizal growth and whether these fungi can access nitrogen locked in soil organic matter; 2) models of pan-Arctic carbon cycling must be modified to include the energy cost to plants of mycorrhizal growth and the accompanying supply of nitrogen to woody plants by mycorrhizal fungi. Broader impacts resulting from the proposed activity include training of graduate and undergraduate students. K-12 students at Barrow (predominately Inupiat Eskimo) will learn about the project and assist in collecting mushrooms and plants through the Barrow Schoolyard program, funded in part by the Arctic LTER project. This research project will set up a partnership between an undergraduate institution and two research institutions. The research findings may create a paradigm shift -- forest and ecosystem scientists must now take into consideration the mycorrhizal symbionts and their role in supplying organic nitrogen from soil to shrubs and trees. Research emphasis will refocus to study the fungal abilities to attack soil organic matter. New measurements must be made of the effects of increased CO2 concentrations and a warming climate on below-ground N cycling and allocation to fungal symbionts. Because this study will provide methods to assess the importance of both C allocation to mycorrhizal fungi and organic N uptake in ecosystems, it will facilitate the inclusion of these important processes in ecosystem C and N models used for management.
