Plant Physiol, May 2001, Vol. 126, pp. 188-202
A Biophysical Analysis of Stem and Root Diameter Variations in
Woody Plants
Michel
Génard,*
Svetlana
Fishman,
Gilles
Vercambre,
Jean-Gérard
Huguet,
Claude
Bussi,
Jacques
Besset, and
Robert
Habib
Unité de Recherche en Ecophysiologie et Horticulture,
Institut National de la Recherche Agronomique, Domaine Saint-Paul, Site
Agroparc, 84914 Avignon cedex 9, France (M.G., G.V., J.-G.H., R.H.);
Department of Statistics and Operations Research, Agricultural Research
Organization, The Volcani Center, Bet Dagan 50250, Israel (S.F.); and
Unité Expérimentale de Recherche Intégrée,
Institut National de la Recherche Agronomique, Domaine de Gotheron,
26320 Saint-Marcel-les-Valences, France (C.B., J.B.)
A comprehensive model of stem and root diameter variation was
developed. The stem (or root) was represented using two coaxial cylinders corresponding with the mature xylem and the extensible tissues. The extensible tissues were assumed to behave as a single cell
separated from the mature xylem by a virtual membrane. The mature xylem
and the extensible tissues are able to dilate with temperature and
grow. Moreover, the extensible tissues are able to shrink and swell
according to water flow intensity. The model is mainly based on the
calculation of water volume flows in the "single cell" that are
described using the principles of irreversible thermodynamics. The
elastic response to storage volume and plastic extension accompanying
growth are described. The model simulates diameter variation due to
temperature, solute accumulation, and xylem, water potential. The model
was applied to the peach (Prunus persica) stem and to
the plum (Prunus domestica × Prunus
spinosa) root. The simulation outputs corresponded well with
the diameter variation observed. The model predicts that variations of
turgor pressure and osmotic potential are smaller than the variations of xylem water potential. It also demonstrates correlations between the
xylem water potential, the turgor pressure, the elastic modulus, and
the osmotic potential. The relationship between the diameter and the
xylem water potential exhibits a subtential hysteresis, as observed in
field data. A sensitivity analysis using the model parameters showed
that growth and shrinkage were highly sensitive to the initial values
of the turgor pressure and to the reflection coefficient of solutes.
Shrinkage and growth were sensitive to elastic modulus and
wall-yielding threshold pressure, respectively. The model was not
sensitive to changes in temperature.
*
Corresponding author; e-mail Michel.Genard{at}avignon.inra.fr;
fax 33-432-72-24-32.
© 2001 American Society of Plant Physiologists
