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JXB Advance Access published online on February 17, 2006
Journal of Experimental Botany, doi:10.1093/jxb/erj085
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Published by Oxford University Press [2006] on behalf of the Society for Experimental Biology. The online version of this article has been published under an Open Access model. Users are entitled to use, reproduce, disseminate, or display the Open Access version of this article for non-commercial purposes provided that: the original authorship is properly and fully attributed; the Journal and the Society for Experimental Biology are attributed as the original place of publication with the correct citation details given; if an article is subsequently reproduced or disseminated not in its entirety but only in part or as a derivative work this must be clearly indicated. For commercial re-use, please contact: journals.permissions@oxfordjournals.org
Received August 9, 2005
Accepted December 5, 2005

RESEARCH PAPER

Impact of defoliation intensity and frequency on N uptake and mobilization in Lolium perenne

F. Lestienne 1, B. Thornton 2, and F. Gastal 1 *

1 Unité d'Ecophysiologie des Plantes Fourragères, INRA, Route de Saintes, F-86600 Lusignan, France
2 Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB15 8HQ, UK

* To whom correspondence should be addressed.
F. Gastal, E-mail: Francois.Gastal{at}lusignan.inra.fr


  Abstract

The aim of the study was to evaluate the impact of defoliation intensity, defoliation frequency, and interactions with N supply on N uptake, N mobilization from and N allocation to roots, adult leaves, and growing leaves. Plants of Lolium perenne were grown under two contrasted N regimes. Defoliation intensity treatments consisted of a range of percentage leaf area removal (0, 25, 50, 75, or 100%). These treatments were applied in parallel to a set of plants previously undefoliated, and to a second set of plants which had been defoliated several times at a constant height. A 15N tracer technique was used to quantify N uptake, mobilization, and allocation over a 7 d period. A significant reduction in plant N uptake was observed with the removal of more than 75% of lamina area, but only with high N supply. As defoliation intensity increased, the amount of N taken up and subsequently allocated to growing leaves during the labelling period was maintained at the expense of N allocation to roots and adult leaves. Increasing defoliation intensity increased the relative contribution of roots supplying mobilized N to growing leaves and decreased the relative contribution of adult leaves. Defoliation frequency did not substantially alter N uptake, mobilization, and allocation between roots, adult and growing leaves on a plant basis. However, tiller number per plant was largely increased under repeated defoliation, hence indicating that allocation and mobilization of N to growing leaves, on the basis of individual tillers, was decreased by defoliation frequency.

Keywords: Defoliation intensity; defoliation frequency; Lolium perenne; N mobilization; N uptake; N supply.
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