Nitrogen_isotope_fraction

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 www.publish.csiro.au/journals/ajpp 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: laurie.martinelli@publish.csiro.au 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: murray.unkovich@nre.vic.gov.au 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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