Sommerkorn Martin

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Sommerkorn
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Nitrate is an important nitrogen source for Arctic tundra plants

2018-03-27 , 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

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.