Variation in Natural Abundance of 15N among Plant Parts and in 15N/14N Fractionation during N2 Fixation in the Legume-Rhizobia Symbiotic System |
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Authors: | Yoneyama Tadakatsu; Fujita Kounosuke; Yoshida Tomio; Matsumoto Tetsuo; Kambayashi Iwao; Yazaki Jinya |
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Institution: | 1Department of Applied Physiology, National Institute of Agrobiological Resources Kannondai, Tsukuba, Ibaraki 305, Japan
2Faculty of Applied Biological Science, Hiroshima University Fukuyama, Hiroshima 720, Japan
3Institute of Applied Biochemistry, University of Tsukuba Sakura-mura, Niihari, Ibaraki 305, Japan
4Dow Chemical Japan Limited 92-2 Ogurano, Gotemba, Shizuoka 412, Japan
5Department of Agricultural Chemistry, Nihon University Setagaya-ku, Tokyo 154, Japan |
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Abstract: | Sixteen legumes were grown in N-free media so that N was suppliedentirely by symbiotic N2 fixation. The plant tissues were analyzedfor natural 15N abundance (expressed as 15N per mil relativeto air N2) with a ratio mass spectrometer. The nodules of desmodium,centro, siratro, soybean and winged bean showed high enrichmentin 15N ( +9 ), while red clover showed slight enrichment ( +2 ).The nodules of 9 other forage legumes (Townsville stylo, whiteclover, alsike clover, common vetch, Chinese milk vetch, senna,alfalfa, ladino clover, and hairy vetch) showed little enrichmentin 15N. In all the legumes investigated, particularly in the ureide-transportingplants such as desmodium, centro, siratro, soybean, winged beanand field bean, the 15N value of the shoots was negative ( 3.2 ).The 15N value of the shoots in winged bean and field bean variedby about 1 depending on the Rhizobium strains used. The isotopicmass balance of 13 legumes indicated that isotopic fractionationoccurs during N2 fixation by the legume-rhizobia symbiosis witha preference for 14N over 15N, resulting in a 15N value of 0.2to 2 in the whole plant. The results indicate that 15N/14N isotopic discrimination witha preference for the lighter atom may occur in both N2 fixationand export of fixed N from nodules.
1Present address: Department of Soils and Fertilizers, NationalAgriculture Research Center, Kannondai, Tsukuba, Ibaraki 305,Japan. (Received October 8, 1985; Accepted April 7, 1986) |
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