Vergara - 1976 - Physiological and morphological adaptability of ri

RICE PR()I>t.T(.'Tl\-"lT‘t' m trumtvrltr REGIONS or JAPAN 459
The close correlation with temperature at Sendai in the earlier half of the
period seems to be attributable to the peculiar soil condition there. The soil of
the experimental field tvas of peaty clay in which. according to Takishima
(1963), reduced toxic substances are usually produced ir1 large amounts in
summer. thereby causing root rot which gives rise to severe withering of lower
leaves from late summer to early autumn. It is quite natural to think that such
injury by toxic substances must be more severe under a higher temperature.
THE EFFICIENCY OF PHOTOSYNTHETIC ORGANS AND CLIMATE
Methods for comparing NAR values among different locations
Many studies have been made on the photosynthetic capacity' of rice varieties 0r
on photosynthetic responses to various environmental factors. However. very
few have succeeded in comparing the photosynthetic ability of unit leaf area
directly among plants grown at different locations. ln the present IBP experiments.
NAR at various stages of growth has been calculated with rice plants
grown at various locations far from each other. supplying the best material for a
direct comparison of the ability for day-matter production.
One of the most important merits of the growth analysis method may be
that it can give NAR tvhich is quite similar in nature to the net photosynthetic
rate determined under conlplctcly‘ natural conditions without the use of any
special techniques or elaborate apparatus. and still tvith fairly high accuracy.
In spite of this. hovt-‘ever. its application often has resulted in rathcr limited
success. One important reason may be that NAR is not only dependent on light
intensity, temperature, and other environmental factors but also is placed
under the strong influence of LAI and plant type. to say nothing about plant
age and other inner factors. Therefore, it is very difficult to compare directly the
values of NAR obtained at various places. unless special design or treatments
have been given to the experiment beforehand. as in the IBP seedling experiments,
It is also very difficult to separate the influence of a single factor, especially
a climatic factor. from the growth analysis data. because many environmental
factors change simultaneously under natural conditions.
Concerning these points. Murata (I975) has succeeded to some extent in
comparing the capability of unit leaf area for dryjmatter production, and in
separating the influence of some climatic factors from others on rice plants
grotvn at different locations and in different years, by treatment of observed
NAR values.
The effect of solar radiation and LA] on NAR
In order to remove the influence of difference in solar radiation level and LAI.
the average light intensity within the leaf layer of a rice stand was calculated in
the following way: According to Monsi and Saeki (1959, the light intensity‘. I.
after passing through F layers of leaves in a plant community can be expressed