Agriculture Reference
In-Depth Information
patterns which may or may not be temperature-dependent. Another impor-
tant aspect, the post-harvest respiration of fruits, is discussed in Chapter
also.
Root respiration
The root respiration of apple trees differs from their shoot respiration in that
it responds to increases in temperature in winter even when very few chilling
units have been accumulated and the overall chilling requirement is not satis-
fied. Under these circumstances, Young (
) found the Q
for respiration,
i.e. the ratio between the rates of respiration at temperature (
T
)
◦
Cto
+
that at
T
◦
C, to be
. However, both respiration rates and the effects of
temperature on these are greater when the chilling requirement is satisfied.
Later in the season, Buwalda
et al.
(
.
) found that root respiration, under
conditions of high irradiation and nitrogen supply, declined from about
.
nmol CO
g
−
dry wt s
−
between
to
days after budburst.
Shadingandlownitrogenalsoreducedrootrespiration.Ebert(
.
and
)foundthat
potassium and phosphorus deficiency, and reduction of the oxygen content in
therootmedium,particularlybelow
%O
,reducerootrespiration.Andersen
et al.
(
), however, found that the respiration rates of roots of
Pyrus
species
and
Cydonia oblonga
(quince) were much less affected by anaerobiosis in solution
culture than were those of
Prunus persica
, being reduced by no more than
%
after
days of anaerobiosis.
Ebert (
) found that the respiration of 'M.
' roots increased linearly with
rising temperature.
Respiration of the above-ground framework
Respiration by the above-ground tree framework (wood respiration) is low
when the trees are dormant. Butler and Landsberg (
) showed that the
respiration of bare branches rises rapidly when physiological activity resumes.
In apple and pear this is dependent on the satisfaction of the winter-chilling
requirement, or chemical treatments to substitute for this, as well as the rise
in temperatures in spring. During endodormancy and the accumulation of
their chilling requirement, apple and pear trees carry on metabolic functions
through maintenance respiration. As trees enter ecodormancy and begin ac-
cumulating heat units respiration usually increases significantly. Young
et al.
(
% of their chilling
requirement before shoot respiration will increase with higher temperatures
during ecodormancy. The Q
for respiration increases from
) concluded that the trees need to have received
as trees
complete their chilling requirement and the respiratory energy of activation
(EA) decreases from
.
to
.
kcal mol
−
. As trees are chilled up to
to
%of
