Agriculture Reference
In-Depth Information
Effects of atmospheric CO
Minchin
et al
.(
) found that lowering CO
in a leaf chamber from a typical
ambient level of
ppm to
ppm reduced the leaf photosynthetic rate from
mol min
−
. Carbon dioxide depletion is not usually considered as
a major factor operating in the orchard.
Corelli-Grappadelli and Magnanini (
µ
.
to
.
) found a doubling of net photo-
mol m
−
s
−
) PAR levels when enclosed mature
cropping trees of 'Golden Delicious'/'M.
synthesis at high (
>
µ
ppm instead of
ambient CO
. The effect of higher CO
levels was smaller at lower light inten-
sities, the net result being that the light response curve was always higher. The
photosynthesis rates at high CO
levels continued to rise with increasing light
intensities well beyond the level at which the photosynthesis/light response
curves at ambient CO
had reached light saturation. This has implications for
potential photosynthesis if atmospheric CO
concentrations rise.
' were fed with
Effects of leaf nitrogen
Kriedemann and Canterford (
) showed that the photosynthesis rates of
nitrogen-deficient pear leaves were only about a quarter as high as those
with high nitrogen levels (Figure
). This effect was associated with lower
chlorophyll levels but the latter explained only about half of the reduction in
photosynthesis. Effects on enzyme production may also be implicated.
.
Effects of leaf type, history and structure
There is ample evidence that leaves exposed to high light levels (sun leaves)
have a higher photosynthetic capacity per unit leaf area than leaves developed
in the shade (Figure
). They have a higher specific leaf weight (mg cm
−
)
as discussed earlier and Barden (
.
) found a close linear relationship (
r
=
.
) between net photosynthesis (
P
n
) and the specific leaf weight of detached
leaves taken from interior (shaded) and peripheral (exposed) positions within
mature apple trees. Campbell
et al
.(
) found that spur leaves from the outer,
high-light zone of apple trees had higher specific leaf weight than interior and
intermediate leaves from full bloom onwards. They consistently throughout
the season had higher net photosynthesis at all light levels and had higher
light saturation levels. These effects may result from the greater number of
palisade layers, and higher chlorophyll and nitrogen content per unit leaf
area commonly found in 'sun' leaves. Asada and Ogasawara (
) found that
leaves of young trees of 'Fuji' grown in the open had maximum photosynthesis
rates of about
mol m
−
s
−
PPFD. Those from trees grown at increasing levels of shade had corresponding
mg CO
dm
−
h
−
at light saturation of
µ
