Agriculture Reference
In-Depth Information
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Figure 8.5
Changes in the rate of leaf photosynthesis of different
leaf types.
,spur leaves 1980;
,spur leaves 1981;
,vegetative
spur leaves 1980;
,basal extension shoot leaves 1981;
•
,
mid-position extension shoot leaves 1981. East Malling,UK. From
Palmer (1986).
Extension shoot leaves show much higher leaf photosynthesis at saturating
light intensity (
Em
−
s
−
) than spur leaves (Figure
). This is in
keeping with their greater thickness and chlorophyll content (Schechter
et al.
,
>
µ
.
).
Effects of sink activity
Numerous studies, reviewed by Avery (
),
have shown that there is greater production of dry matter per unit leaf area
by fruiting than by defruited trees. Expressed as average net assimilation rates
over the season, Avery (
,
) and Flore and Lakso (
) calculated that the leaves on fruiting trees were
% more efficient. Some of the implicit enhancement of photosynthesis by
fruiting may have been due to poorer leaf development, therefore less shaded
canopies, in the cropping trees. In a number of cases, however, the presence of
fruit caused an increase in total dry matter production (Chandler
; Maggs
).
Direct measurements have confirmed that the presence of fruits can lead
to substantial enhancement of photosynthesis (Avery
;Avery
; Lenz
; Palmer
). There have also been many experiments in which
no such effects were demonstrated, possibly as a result of experimental con-
ditions in which photosynthesis was source-limited or non-fruit sinks were
of dominant importance (Flore and Lakso,
; Greer
et al.
,
). Palmer (
) compared
heavily cropping trees of 'Crispin'/'M.
' with ones thinned to various lev-
els, including complete deblossoming, under English conditions. Only in July
