Agriculture Reference
In-Depth Information
Antoszewski (
) found that photosynthesis rates on the east sides of north-
south oriented hedgerows peaked in mid-morning, and those on the west sides
in the early afternoon, reflecting the daily course of illumination on the two
sides.
Effects of leaf age
Kennedy and Fuji (
) found that, following apple leaf emergence in spring,
net photosynthesis at saturating irradiance increased rapidly as the leaves
expanded, reaching a peak of
mg CO
dm
−
h
−
at about
to
-
%of
full leaf expansion. Rates then dropped by about
% to a plateau which could
be maintained for more than
months, to mid-October, before beginning a
rapid decline. Porpiglia and Barden (
) found that well-exposed apple spur
leaves showed little change in photosynthesis for about
months. In contrast,
Palmer (
) and others have found ageing effects from quite early in the
season (Figure
.
).
Seasonal patterns
Seasonal patterns reflect the ageing of individual leaves, which has been slow
in most studies, and a very rapid decline due to, or triggered by, environmental
factors at the end of the season. Cheng and Luo (
), measuring photosyn-
thesisinthefield,foundverylittledeclineinthedailymaximumphotosynthesis
rate of mid-position shoot leaves in Shandong, China, over the months of May
to October inclusive but a sharp decline in daily total CO
gain in September
and, especially, October. This appears to relate to the lower irradiance and
leaf temperatures in the later part of the day in those months. Lakso and Lenz
(
) found that autumnal senescence and reduction in photosynthesis could
be stopped by transferring apple trees to a regime with higher temperatures
(
◦
Cday,
◦
C night) than those obtaining outdoors.
Photosynthesis by flowers, fruits and stems
These organs may contain chlorophyll and fixcarbon dioxide. Vemmos and
Goldwin (
) found that before flower opening, sepals and receptacles
hadchlorophyllconcentrationssimilartothosefoundinrosetteleavesalthough
they decreased subsequently. At the green-cluster stage flowers contributed
,
%tothenumber
of stomata of floral clusters. Flower gross photosynthesis was about a third of
thatofleavesattheballoonstageandat
%tothegreensurfacearea,
%tototalchlorophylland
daysafterfullbloom,althoughmuch
less at full bloom. Photosynthesis by flowers apparently contributed
-
%
of their own carbohydrate need.
