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Titre :
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Nitrogen reserve mobilization during regrowth of Medicago sativa L. Relationships between availability and regrowth yield
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Auteurs :
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A. Ourry ;
T. Kim ;
J. Boucaud
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Type de document :
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article/chapitre/communication
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Année de publication :
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1994
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Format :
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831-837
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Langues:
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= Anglais
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Mots-clés:
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Azote
;
Croissance
;
Carbone
;
Translocation
;
Remobilisation
;
Medicago sativa
;
Leguminosae
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Résumé :
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An experiment was designed to study the role of N and C reserves on regrowth of the shoots following defoliation of forage species. Starch and N accumulation in root and crown tissue of nonnodulated Medicago sativa L. were modified during regrowth by applying different levels of N and different cutting heights. Plants were obtained with similar crown and root dry weights, but having either low starch and high tissue N or high starch and low tissue N. The plants were then submitted to a second defoliation and supplied with optimal N nutrition, and N flow from reserve was quantified using pulse-chase N-15 labeling. Maximum yields following the second regrowth were obtained from those plants having a high tissue N, despite their low level of nonstructural carbohydrate. When N in the roots and crown exceeded 5 mg N plant(-1) at the beginning of regrowth, about 68% was translocated to regrowing shoots. Highly significant correlations were also found between the amounts of N available in roots and crown at the beginning of regrowth and (a) the amount of N that was mobilized to new tissues, (b) the amount of N taken up during the regrowth period, and (c) the final shoot yield after 24 d of regrowth. No similar correlations were found for plants that varied in their initial starch content of roots and crown. It is suggested that N reserves were used mainly during the first 10 d after defoliation, and that the resulting aerial growth during this period should be sufficient to restore N-2 fixation and/or N uptake to levels equal to those prior to defoliation. These data emphasize (a) the importance of root N reserves in initiating and sustaining new shoot growth, and (b) the need for a re-evaluation of the contribution of C reserves to shoot regrowth.
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Source :
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Plant Physiology - 0032-0889, vol. 105, n° 3
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