Browsing by Author "Koba, Keisuke"

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Nitrate is an important nitrogen source for Arctic tundra plants
(2018-03) 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.