Nitrate is an important nitrogen source for Arctic tundra plants

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Liu, Xue-Yan
Koba, Keisuke
Koyama, Lina A.
Hobbie, Sarah E.
Weiss, Marissa S.
Inagaki, Yoshiyuki
Shaver, Gaius R.
Giblin, Anne E.
Hobara, Satoru
Nadelhoffer, Knute J.
Sommerkorn, Martin
Rastetter, Edward B.
Kling, George W.
Laundre, James A.
Yano, Yuriko
Makabe, Akiko
Yano, Midori
Liu, Cong-Qiang
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Arctic tundra plants
Nitrogen dynamics
Plant nitrate
Soil nitrate
Stable isotopes
Plant 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.
© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Proceedings of the National Academy of Sciences.of the United States of America 115 (2018): 3398-3403, doi:10.1073/pnas.1715382115.
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Proceedings of the National Academy of Sciences.of the United States of America 115 (2018): 3398-3403
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