Vergara - 1976 - Physiological and morphological adaptability of ri

234 CLIMATE AND RICE
Rule of carbon ossmitntion (QCOZ-rrfzhetd/hr)
7
6_
O | | | | | | | 1 I | I
O OI 0.2 O3 0.4 O5 O6 OT O8 O9 IO Ii t2
l-iql" hlfitiity (cul- cm'2 - min")
4. Relationship between light intensity and photosyntlhetic
rates in rice populations with horizontal leaves
t‘ ‘l and vertical leaves (O
O) (Tanak1l972)
The relationships between leaf angle and photosynthesis in a rice population
with LA] of 7.1 were observed by T. Tanaka (I972). The light density fell
gradually as light penetrated into the population with vertical leaves, but
rapidly as it entered the population with horizontal leaves. For example, at
heading time. 90 of the daylight was intercepted in the vertical distance of 30
cm in the rice population with horizontal leaves. while the percentage intercepted
in the same vertical distance in the rice population with vertical leaves
was 50% of the daylight. Figure 4 shows that the photosynthesis in the population
with vertical leaves increased with light intensity and did not reach saturation.
while in the population with horizontal leaves, it increased with light
intensity up to about 0.6 cal -cm'* - min-k and above this became light-saturated.
In this experiment. the grain yield in the rice population with horizontal leaves
was 33% less than that in the rice population with vertical leaves. Thus, it
seems that a rice population with vertical leaves is one of the most important
characteristics for increasing grain yield.
The leaves in a plant population receive light on both obverse and reverse
rides. Under diffused solar radiation, the obverse and reverse sides of leaves
receive light equally. This is true in the population with vertical leaves rather
than in the population with horizontal leaves. On the other hand, under direct
solar radiation. the leaves in a population receive light strongly on one of two
sides. The leaves in the lower layer of a population receive more abundant
light under diffused radiation than under direct radiation (Ito, 1971). The
photosynthesis in plant populations such as rice, soyfbeail, and sugar beet
increased with increasing percentage of diffused light to total solar radiation
(Kumura. 1968; Ito, 197111‘. Tanaka, 1W2).