JXB Advance Access originally published online on May 4, 2007
Journal of Experimental Botany 2007 58(8):2091-2099; doi:10.1093/jxb/erm065
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RESEARCH PAPER |
Experimental evaluation of an efflux–influx model of C exudation by individual apical root segments
1UMR INPL(ENSAIA)-INRA Agronomie et Environnement Nancy-Colmar, 2 avenue de la forêt de Haye, F-54500 Vandoeuvre lès Nancy, France
2Unité de recherche Plantes et Systèmes de Cultures Horticoles, INRA Domaine Saint-Paul - Site Agroparc, F-84914 Avignon, France
* Present address and to whom correspondence should be sent: UMR 1220 INRA-ENITAB Transfert sol-plante et cycle des éléments minéraux dans les écosystèmes cultivés, 71, avenue Edouard Bourlaux, BP 81, F-33883 Villenave d'Ornon, France. E-mail: Christophe.Nguyen{at}bordeaux.inra.fr
The aim of this study was to evaluate if a model describing the efflux and the influx of C through the root surface could be fitted to experimental short-term kinetics of carbon (C) exudation by individual apical root segments in maize (Zea mays L.). The efflux of C was set constant or modelled by a power function of the distance from the apex to simulate the greater release of C around the root tip commonly reported in the literature. The influx was proportional to the C concentration in the external solution to simulate the active re-uptake of exudates by the root. Plants were exposed to full light or to shade to manipulate C allocation to roots. The model with a constant efflux gave satisfactory fits to the kinetics of exudation (average R2=0.66). The average gross efflux was then 2.1 µg C cm–2 root surface h–1. The model was improved if exudation was set more intense towards the root apex (average R2=0.74). The estimated gross efflux decreased then from 5.2 µg C cm–2 h–1 at the apex to 1.8 µg C cm–2 h–1 for the region located 5–25 cm from the root tip. The decrease in net exudation of individual roots due to the shading of plants was weak, which may indicate that the import of C by the primary roots studied was not reduced significantly. By describing the exudation of an apical root segment of variable length and diameter, the model is a first step in linking exudation to root system architecture models and to whole plant functioning.
Key words: Carbon, exudation, model, root apex, root length, root diameter
Received 21 December 2006; Revised 28 February 2007 Accepted 6 March 2007
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