title: Experimental evaluation of an efflux-influx model of C exudation by individual apical root segments.
abstract: 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 R(2)=0.66). The average gross efflux was then 2.1 mug C cm(-2) root surface h(-1). The model was improved if exudation was set more intense towards the root apex (average R(2)=0.74). The estimated gross efflux decreased then from 5.2 mug C cm(-2) h(-1) at the apex to 1.8 mug 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.
authors.affiliation: UMR INPL(ENSAIA)-INRA Agronomie et Environnement Nancy-Colmar, 2 avenue de la forêt de Haye, F-54500 Vandoeuvre lès Nancy, France.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Personeni
authors.forename: Christophe
authors.initials: C
authors.lastname: Nguyen
authors.forename: Patrice
authors.initials: P
authors.lastname: Marchal
authors.forename: Loïc
authors.initials: L
authors.lastname: Pagès
mesh_terms: D001692:Biological Transport; D002244:Carbon / Q000378:metabolism*; D007700:Kinetics; D008954:Models, Biological; D018517:Plant Roots / Q000378:metabolism; D012996:Solutions / Q000737:chemistry; D014871:Water Microbiology; D003313:Zea mays / Q000033:anatomy & histology / Q000378:metabolism*
chemical_list: D012996:Solutions; D002244:Carbon