Liu, Xue-YanKoba, KeisukeKoyama, Lina A.Hobbie, Sarah E.Weiss, MarissaInagaki, YoshiyukiShaver, Gaius R.Giblin, Anne E.Hobara, SatoruNadelhoffer, Knute J.Sommerkorn, MartinRastetter, Edward B.Kling, George W.Laundre, James A.Yano, YurikoMakabe, AkikoYano, MidoriLiu, Cong-Qiang2018-05-302018Liu, X., K. Koba, L. A. Koyama, S. E. Hobbie, M. S. Weiss, Y. Inagaki, G. R. Shaver, et al. 2018. “Nitrate is an important nitrogen source for Arctic tundra plants.” Proceedings of the National Academy of Sciences of the United States of America 115 (13): 3398-3403. doi:10.1073/pnas.1715382115. http://dx.doi.org/10.1073/pnas.1715382115.http://nrs.harvard.edu/urn-3:HUL.InstRepos:37068309Plant nitrogen (N) use is a key component of the N cycle in terrestrial ecosystems. The supply of N to plants affects community species composition and ecosystem processes such as photosynthesis and carbon (C) accumulation. However, the availabilities and relative importance of different N forms to plants are not well understood. While nitrate (NO3−) is a major N form used by plants worldwide, it is discounted as a N source for Arctic tundra plants because of extremely low NO3− concentrations in Arctic tundra soils, undetectable soil nitrification, and plant-tissue NO3− that is typically below detection limits. Here we reexamine NO3− use by tundra plants using a sensitive denitrifier method to analyze plant-tissue NO3−. Soil-derived NO3− was detected in tundra plant tissues, and tundra plants took up soil NO3− at comparable rates to plants from relatively NO3−-rich ecosystems in other biomes. Nitrate assimilation determined by 15N enrichments of leaf NO3− relative to soil NO3− accounted for 4 to 52% (as estimated by a Bayesian isotope-mixing model) of species-specific total leaf N of Alaskan tundra plants. Our finding that in situ soil NO3− availability for tundra plants is high has important implications for Arctic ecosystems, not only in determining species compositions, but also in determining the loss of N from soils via leaching and denitrification. Plant N uptake and soil N losses can strongly influence C uptake and accumulation in tundra soils. Accordingly, this evidence of NO3− availability in tundra soils is crucial for predicting C storage in tundra.en-USEcologyEnvironmental SciencesArctic tundra plantsnitrogen dynamicsplant nitratesoil nitratestable isotopesJournal Article2018-05-3010.1073/pnas.1715382115