Vergara - 1976 - Physiological and morphological adaptability of ri

116 CLIMATE AND RICE
about the microclirnatc of the rice crop has been obtained for lovrland than for
upland rice. Since the physical principles governing the exchange of atmospheric
constituents between vegetative surfaces and the air are identical for the two
ecotypes, the characteristics ofmicroclimate described here can be also applied
to the microclimate of upland rice.
CANOPY STRUCTURE
Since Murata (1961) and Tsunoda (1964) pointed out the importance ofcanopy'
structure for increasing rice yield. a number of agricultural techniques have
been used in attempts to manipulate the display of leaves in the rice canopy
(e.g. Tsunoda. 1964; Tanaka, 1W2; Matsushima. 1973). More recently. Tanaka
et al. (1968) compared values of the light-extinction coefficient among rice
cultivars with different yielding capacities, and found that the extinction coefficient
was smaller for modern high-yielding varieties than for old loiv-yrielding
varieties.
Although research led to the “plant type concept" as a guide for breeding
high-yielding varieties of rice, relatively! few studies have been made of the
geometrical structure (architecture) of the rice crop. The geometrical structure
of plant canopies can be specified collectively by the leafarea-density’ function
a(z). the leaf-inclination-density function aUBL). and the leaf-azimuth-densityr
function a(j L), where z is the height above the ground or water surface, 15L. is
the inclination angle ofa leaf. and j L is the azimuth angle ofa normal leaf.
The leaf-area-density function of well-grown rice canopies is characteristic
of grasses and may be represented by a curve with its maximum in the middle
layer of the canopy. Figure 1 shows the change in leaf-inclination-density function
of rice crops ivith plant development. Before heading time. most leaves are
arranged in the inclination angle intewal 60°—90°. implying that rice crops
behave like an erectophile canopy (defined by de Wit, 1965). Although cultivar
1R8 retained an erectophile structure throughout the whole grovring season, the
canopy structure of the cultivar Manryo clearly changed from an erectophile to
a plagiophile type Willi the development of flag leaves and ears. A similar trend
of the leaf arrangement with the growth of plant was also observed with cultivar
Honeriivase (Ito, 1969).
In Fig. l, X represents the “leaf-area inclination index" derived by Ross and
Ross (1969) to characterize the canopy structure of plants. 1t is defined by
x = 0.5[|0.|3 - g,*| + |0.3? - g2*| + |0.50 - g,,*|] (1)
where g,*, g,*. and g3‘ are the leaf area fractions in each of the inclination angle
intervals U°—30°, 30°—60°, and 60°—90°. respectively. Values of X in Fig. 1 clearly’
denote that the IRS canopy is more erectophile than the Mamyo canopy
throughout the groiving season. Stratum-bjr-stratum treatments made before
and after heading revealed that the canopy structure of the cultivar Manryo