Journal of Experimental Botany, Vol 49, 1245-1257, Copyright © 1998 by Oxford University Press
J Masle
Leaf growth and stomatal behaviour are sensitive to variations in soil
mechanical resistance to penetration (Rs). That
resistance is strongly influenced by soil water constant, density and
texture. As such it is therefore an inherently variable and changing
characteristic of the roots natural environment. Leaf responses to spatial
and temporal variations in Rs were analysed in wheat
using two kinds of simplified model systems: (a) bi-layered soils made of
either a low Rs layer on top of a high
Rs layer, or the converse, (b) soils where, after
enduring high Rs, the whole root system was suddenly
exposed to lower Rs by raising soil water content.Both
leaf expansion rate and stomatal conductance responded to some roots
meeting a new soil layer and also to a step change in impedance to the bulk
of roots. These responses could not be ascribed to variations in water or
nutrient status per se and strengthen the case for the
involvement of some kind of chemical signalling of Rs
to leaf cells. Moreover, a striking and novel feature of these responses is
that they were always detected with a significant time-lag after the change
in Rs had first been experienced. It is concluded that
leaf biological age is a paramount factor in explaining such a lag. These
data reveal that leaf sensitivity to Rs is mostly
confined to early developmental stages preceding blade emergence. However,
they also point to the contribution of additional factors, raising the
questions of the role of root parts behind the tip and of threshold-type
leaf responses to stress induced root signals.Keywords:
Soil strength, root impedance, bi-layered soil, wheat, leaf
expansion, stomatal conductance, critical biological age.
ARTICLES
Growth and stomatal responses of wheat seedlings to spatial and temporal variations in soil strength of bi-layered soils
Research School of Biological Sciences, Australian National University, GPO Box 475, Canberra, ACT, Australia 2601; e-mail: masle@rbs-central.anu.edu.au
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