Ecosystem Ecology Laboratory

Diversity of Ericoid Mycorrhizal Fungi and its Significance in Plant Nitrogen Acquisition in the Arctic

Ari Jumponnen and Loretta Johnson

Biological diversity and its function are focal areas in ecology. The relationship between plant diversity and ecosystem function has been intensively studied. In contrast, few studies have addressed the role of mycorrhizal fungi and their diversity even though they are presumed critical in plant nutrient uptake and nutrient retention. This proposal focuses on differential nitrogen (N) use among symbiotic fungi colonizing roots of ericaceous dwarf shrubs in the arctic. Specifically, we address the role of diverse ericoid mycorrhizal fungi in facilitating plant access to organic and inorganic N sources. Indeed, ericoid mycorrhizal (ERM) symbiosis may be the key to the abundance of ericaceous shrubs in arctic ecosystems. Thus, knowledge of ERM diversity and its function is a necessary foundation for understanding arctic and boreal ecosystem processes. This knowledge is especially crucial in arctic ecosystems where supply of inorganic N is low and plant N limitation is strong.

Proposed research: Six specific objectives are included: (1) ERM fungal diversity in roots of ericaceous plants will be estimated using pure culture studies and direct polymerase chain reaction (PCR) with rDNA analyses. ERM fungi will be isolated from ericaceous plants at the Toolik Lake Arctic Long Term Ecological Research site. These pure culture estimates of fungal species composition will be complemented by direct PCR from roots of five ericaceous plant species. This will allow evaluation of ERM fungal diversity using two complementary methods. (2) Differential use of organic and inorganic N among ERM fungi will be quantified. Fungal cultures will be grown with different N sources (NH4+, NO3-, bovine serum albumen, alanine, glycine and arginine) in growth medium and fungal growth quantified. (3) Differential N utilization by intact host plants inoculated with fungal cultures will be assessed. Plant growth and N acquisition will be evaluated in growth chamber experiments with different N sources (as above). (4) Plant uptake of intact amino acids will be determined in growth chamber experiments utilizing 13C- and 15N-labeled amino acids. This tracer experiment will allow us to assess whether plants and ERM fungi take up intact amino acids or if ERM metabolize amino acids prior to plant uptake. (5) Importance of greater fungal diversity in plant N uptake will be tested. One or several fungi will be inoculated on intact plants and plant growth and N use determined in a growth chamber experiment. (6) Relevance of fungal diversity in plant N uptake will be tested in the field. Sites with fungicide-reduced fungal diversity will be compared to controls in an experiment in which 13C- and 15N-labeled amino acids will injected into the tundra and plant N uptake determined. The last experiment tests whether ERM plants bypass competition for N with saprobic microbes.

Broader impacts: This proposal extends biodiversity research into a new avenue of inquiry: the functional role of ERM fungi in the arctic. This research will significantly improve our understanding of how fungal diversity relates to plant nutrient uptake in organic-N-rich arctic soils and ultimately improve our knowledge of mechanisms of plant nutrient retention and cycling in arctic ecosystems. Both investigators have productive research programs in alpine or arctic ecosystems and a history of disseminating their results in national and international forums. The proposed research has a significant training component: one post-doctoral associate, two graduate students and at least two undergraduate students. Both investigators have a track record of training women/minorities in biology. They have a demonstrated commitment to undergraduate and graduate training in order to provide students stimulating experiences in ecology. The proposed studies will also establish an innovative research collaboration between a molecular ecologist (Jumpponen) and terrestrial ecosystem ecologist (Johnson) at Kansas State University.

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