Nitrogen_isotope_fraction - CSIRO PUBLISHING AUSTRALIAN...

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CSIRO PUBLISHING A USTRALIA N J OURNA L OF P LANT P HYSIOLOGY Volume 27 , 2000 © CSIRO 2000 An international journal of plant function All enquiries and manuscripts should be directed to Australian Journal of Plant Physiology CSIRO PUBLISHING PO Box 1139 (150 Oxford St) Collingwood Telephone: 61 3 9662 7625 Vic. 3066 Facsimile: 61 3 9662 7611 Australia Email: [email protected] Published by CSIRO PUBLISHING for CSIRO and the Australian Academy of Science
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Introduction Extensive research in recent years (see review of Hogberg 1997) has improved our understanding of natural variations in the abundance of the stable isotope 15 N ( δ 15 N) within plant–soil systems, and how these might be gainfully exploited in field studies of plant N acquisition. Since atmos- pheric N 2 has a constant 15 N abundance (0.3663 atom%) it is used as the standard (0‰) against which natural variations in δ 15 N are measured, and although soil δ 15 N is much more variable than atmospheric N 2 , there is a strong tendency for it to be lightly enriched in 15 N (0.5–5‰) relative to the atmo- sphere. In annual agricultural ecosystems, these variations in δ 15 N have been used to estimate the percentage of legume N derived from the atmosphere (%Ndfa) as opposed to soil N sources (Peoples et al. 1989). In the case of perennial legumes and in natural ecosystems, the methodology has many more complications (Handley and Scrimgeour 1997), although δ 15 N-based investigations have proved useful for examining plant N acquisition strategies of shrubs and trees in some field studies (e.g. Hogberg 1990; Stewart et al. 1993; Pate et al. 1998). The complications principally relate to fractionation of N isotopes as N moves from one pool to another within the soil (Hogberg 1997) and within the plant (Yoneyama 1995), and so before one can confidently use δ 15 N to assess N acquisition strategies of perennial plants in a given ecosystem, an examination of the variations of 15 N within these pools is required. Aust. J. Plant Physiol. , 2000, 27 , 921–929 10.1071/PP99201 0310-7841/00/100921 Abbreviations used: DAS, days after sowing; DM, dry matter; %Ndfa, percentage of plant N derived from the atmosphere; δ 15 N, stable isotope 15 N. © CSIRO 2000 Nitrogen isotope fractionation in the fodder tree legume tagasaste ( Chamaecytisus proliferus ) and assessment of N 2 fixation inputs in deep sandy soils of Western Australia Murray J. Unkovich ABC , John S. Pate AB , Edward C. Lefroy A and David J. Arthur B A Centre for Legumes in Mediterranean Agriculture, and B Department of Botany, The University of Western Australia, Nedlands, WA 6907, Australia. C Present address: Victorian Institute for Dryland Agriculture, Mallee Research Station, Walpeup, Vic. 3507, Australia. Corresponding author; email: [email protected] Abstract. Nitrogen (N) isotope fractionation and symbiotic N fixation were investigated in the shrub legume tagasaste, growing in the glasshouse and field. In a pot study of effectively nodulated plants supplied with 0, 1, 5 and 10 m M nitrate [stable isotope 15 N ( δ 15 N) of 3.45‰], the δ 15
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Nitrogen_isotope_fraction - CSIRO PUBLISHING AUSTRALIAN...

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