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Intra-trophic isotopic discrimination of N-15/N-14 for amino acids in autotrophs: Implications for nitrogen dynamics in ecological studies

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Title: Intra-trophic isotopic discrimination of N-15/N-14 for amino acids in autotrophs: Implications for nitrogen dynamics in ecological studies
Authors: Takizawa, Yuko Browse this author
Dharampal, Prarthana S. Browse this author
Steffan, Shawn A. Browse this author
Takano, Yoshinori Browse this author
Ohkouchi, Naohiko Browse this author
Chikaraishi, Yoshito Browse this author
Keywords: food web
isotopic fractionation
plant phenology
trophic position
winter dormancy
delta N-15
Issue Date: 22-Mar-2017
Publisher: John Wiley & Sons
Journal Title: Ecology and evolution
Volume: 7
Issue: 9
Start Page: 2916
End Page: 2924
Publisher DOI: 10.1002/ece3.2866
Abstract: The differential discrimination of nitrogen isotopes (N-15/N-14) within amino acids in consumers and their diets has been routinely used to estimate organismal tropic position (TP). Analogous isotopic discrimination can occur within plants, particularly in organs lacking chloroplasts. Such discrimination likely arises from the catabolic deamination of amino acids, resulting in a numerical elevation of estimated TP, within newly synthesized biomass. To investigate this phenomenon, we examined the 15N/14N of amino acids (delta N-15(AA)) in spring leaves and flowers from eight deciduous and two annual plants. These plants were classified on the basis of their time of bloom, plants that bloomed when their leaves were absent (Type I) versus plants that bloomed while leaves were already present (Type II). Based on the delta N-15(AA) values from leaves, both plant types occupied comparable and ecologically realistic mean TPs (= 1.0 +/- 0.1, mean +/- 1 sigma). However, the estimated TPs of flowers varied significantly Type I: 2.2 +/- 0.2; Type II: 1.0 +/- 0.1). We hypothesize that these results can be interpreted by the following sequence of events: (1) Type I floral biomass is synthesized in absence of active photosynthesis; (2) the catabolic deamination of amino acids in particular, leaves behind N-15 in the residual pool of amino acids; and (3) the incorporation of these N-15-enriched amino acids within the biomass of Type I flowers results in the numerical elevation of the TPs. In contrast, the actively photosynthesizing Type II leaves energetically sustain the synthesis of Type II flower biomass, precluding any reliance on catabolic deamination of amino acids. Amino acids within Type II flowers are therefore isotopically comparable to the Type II leaves. These findings demonstrate the idiosyncratic nature of the delta N-15(AA) values within autotrophic organs and have implications for interpreting trophic hierarchies using primary producers and their consumers.
Rights: [Intra-trophic isotopic discrimination of 15N/14N for amino acids in autotrophs: Implications for nitrogen dynamics in ecological studies/Yuko Takizawa, Prarthana S. Dharampal, Shawn A. Steffan, Yoshinori Takano, Naohiko Ohkouchi, Yoshito Chikaraishi/Ecology and Evolution 7/9. Copyright (c) [2017] [ Yuko Takizawa, Prarthana S. Dharampal, Shawn A. Steffan, Yoshinori Takano, Naohiko Ohkouchi, Yoshito Chikaraishi].
http://creativecommons.org/licenses/by/4.0/
Type: article
URI: http://hdl.handle.net/2115/67033
Appears in Collections:低温科学研究所 (Institute of Low Temperature Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 滝沢 侑子

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