A Non-Native Riparian Tree (Elaeagnus angustifolia) Changes Nutrient Dynamics in Streams
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Russian olive (Elaeagnus angustifolia) is a non-native riparian tree that has become common and continues to rapidly spread throughout the western United States. Due to its dinitrogen (N2)-fixing ability and proximity to streams, Russian olive has the potential to subsidize stream ecosystems with nitrogen (N), which may in turn alter nutrient processing in these systems. We tested these potential effects by comparing background N concentrations; nutrient limitation of biofilms; and uptake of ammonium (NH4-N), nitrate (NO3-N), and phosphate (PO4-P) in paired upstream-reference and downstream-invaded reaches in streams in southeastern Idaho and central Wyoming. We found that stream reaches invaded by Russian olive had higher organic N concentrations and exhibited reduced N limitation of biofilms compared to reference reaches. However, at low inorganic N background concentrations, reaches invaded by Russian olive exhibited higher demand for both NH4-N and NO3-N compared to their paired reference reaches, suggesting these streams have the potential to retain the N subsidy from Russian olive N2 fixation and diminish its downstream export and effects. Our findings demonstrate the potential for a non-native riparian plant to significantly alter biogeochemical cycling in streams. Finally, we used our results to develop a conceptual model that describes predicted effects of Russian olive and other non-native riparian N2 fixers on in-stream N dynamics.
KeywordsElaeagnus angustifolia Russian olive invasive species nitrogen fixation nutrient limitation nutrient spiraling subsidy DON
We would like to thank all private land owners who granted us access to many of our study sites as well as the U.S. Forest Service, Bureau of Reclamation, and Shoshone-Bannock Tribe of Fort Hall for additional site access. We sincerely thank The Nature Conservancy of Wyoming for providing housing while we were conducting research in WY. We thank Teresa Tibbets who was instrumental in site selection in WY and reviewed an earlier draft of this manuscript for her help and encouragement. Thanks to Richard Inouye, G. Wayne Minshall and two anonymous reviewers for helpful reviews of this manuscript. We thank Jessica Lueders-Dumont, Hannah Harris, Jennifer Cornell, Tiffany Cook, Tyler Auck, J. Ryan Bellmore, Rebecca Martin, and Amanda Rugenski for their assistance in the field and laboratory. Ian Washbourne at USU performed laboratory chemistry analyses. Funding for this research was provided by NSF EPSCoR in Idaho (EPS-0447689 and EPS-08-14387) and NSF DDIG (Grant # 0910367).
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