Agriculture Reference
In-Depth Information
their chilling requirement, their respiratory quotient (the ratio of CO
evolved
to O
consumed in respiration) increases from
. This may indicate
a shift from the use of lipids as a significant substrate for respiration early
in the dormancy period, to carbohydrates. The respiration of both bud and
internode tissue increases under warm temperatures after adequate chilling.
This indicates that physiological changes related to carbohydrate utilization
occur throughout the shoot during budbreak.
Stem respiration peaks at about the time the leaves emerge from the buds,
presumably at the time of maximum mobilization of reserves. In England the
calculated peak of about
.
to
◦
C values) occurred
in late April, and by late May had fallen to half of this (Butler and Landsberg,
mg m
−
surface area s
−
(
.
).
Leaf respiration
Leaf dark respiration (
R
d
) per unit area is greatest at full bloom and immedi-
atelyafterward,andthendeclines.
R
d
isgreaterinleavesfromtheexteriorparts
of apple trees, well exposed to light, than in leaves from inner or intermediate
zones (Porpiglia and Barden,
; Campbell
et al.
,
). At full bloom and
mol m
−
s
−
full bloom
+
weeks, Campbell
et al.
(
) found rates of
.
µ
mol m
−
s
−
for interior leaves, declining to
for exterior leaves and
.
-
.
µ
.
for exterior leaves and
.
-
.
for interior leaves during the period from
full bloom
+
weeks to full bloom
+
weeks. Porpiglia and Barden (
)
mg CO
dm
−
h
−
in early May to about
found a decline from about
.
mg CO
dm
−
h
−
in August and September for exposed leaves and cor-
respondingly lower values for interior leaves. The differences in
R
d
between
sun and shade leaves is reduced if respiration is expressed per unit leaf weight
instead of area. Barden (
) showed that, as with photosynthetic rate and
specific leaf weight, artificial shading could induce changes in
R
d
even after
leaf expansion ceased. Leaf dark respiration is greater in fruiting than in non-
fruiting trees. This may be partly due to stomata opening wider and staying
open to later in the evening in the fruiting trees (Blanke,
). Temperature is
the dominant environmental factor controlling leaf respiration. Watson
et al.
(
) showed an excellent linear relationship between the logarithm of leaf
dark respiration and temperature,
R
d
increasing ten-fold between
◦
C and
◦
C (Figure
e
kT
where
k
.
) according to the equation
R
d
=
.
=
.
.
Higgins
et al.
(
) found a similar temperature effect for apple, with a
k
value
of
, and appreciably lower
R
d
values for Asian pear.
Proctor
et al.
(
.
) found
R
d
values for the stems and leaves of leafy shoots
of 'Golden Delicious' apple to be similar whether on a dry weight or a fresh
weight basis (Table
.
), but the dark respiration of leafy shoots little more
◦
C and
◦
C.
than doubled between
