Agriculture Reference
In-Depth Information
which corresponded with that of new root growth. There is, however, evidence
that calcium uptake by white and woody roots per unit of root surface area
is similar (
nmol Ca
+
mm-
h
−
respectively), and that at some
times of year brown roots make up
.
and
.
% of the root length of young fruit trees
and so must provide the absorbing surface (Atkinson and Wilson,
). The
zone just behind the root tip, with its root hairs, both provides the greatest sur-
faceperunitlengthofrootandalsoisinundepletedsoil.Theoldersecondarily-
thickened roots are likely to have better root-soil contact than white roots
(Wilson and Atkinson,
). These factors are likely to influence the impor-
tance of different parts of the root system in nutrient uptake. Uptake by the
rootsfromthesoilisfrequentlyineffectiveinsupplyingenoughcalciumtofruits
toensureoptimalstoragelife,andothernutrientssometimeshavetobeapplied
as foliar sprays. This is discussed in Chapters
and
.
Storage of reserves
Growth and fruiting of apple and pear trees in the spring must depend, in their
early stages, on mobilization of reserves accumulated in the previous season.
Many of these are held in the roots.
Hansen (
) found that
labelled
CO
supplied to apple leaves in the autumn was mainly trans-
ported down to the roots. In the spring
C was detected in all new leaf and
shoot growth, with the greatest activity in the first-formed leaves. Hansen and
Grauslund(
), Quinlan (
) and Hansen and Grausland (
%ofthe
Cinthetreeson
)found
Novembertobeinthe
roots and a further
% in the rootstock. There was then a rapid decline in the
amount of
C in these tissues, especially between
January and
May when
it was only about
% of the November value. Most of this loss was attributed
to respiration, about
% of it to building materials for new growth.
The quantities of carbohydrate stored in the roots are large. Murneek (
)
found that the roots of
-year-old apple trees in mid-October contained
up to
% for the above-ground parts.
Hemicellulose was the major carbohydrate fraction but there is controversy as
to whether this functions as reserve as well as structural material. Starch was
the main storage carbohydrate, making up
% carbohydrates compared with
% of the dry weight, and sorbitol
the main soluble carbohydrate. Sucrose, glucose and fructose are also present
(Hansen and Grauslund,
).
Total N concentration in winter is about
.
% in the roots of well-fertilized
young apple trees and about
.
% is mobilized in spring (Tromp,
). The
