Vergara - 1976 - Physiological and morphological adaptability of ri

(_'[.l\l.A'l'IC INFLUENCE ON PHOTOSYNTHESIS AND RESPIRATION 227
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l. Changes in tCIHpef-‘Ztlillfe-pl10tOSYfllheSlS curves of
rice as afTeeted by atmospheric O_ concentration and 11i-
Lrogen fertilization (Akita. unpublished).
ished rapidy at temperatures below‘ 20°C or above 40°C. Takeda (1961) indicated
that the optimum temperature for gross photosynthesis ofjaponiea rice
ranged from 18° to 32°C. Osada (1964) reported that the detached leaves of indiea
rice grown in Ceyfilcm had optimum gross photosynthesis at temperature
between 25° and 35°C. and at 20°C or 40°C shmi-"ed decreased photosynthesis.
This suggests that the temperature response of photosynthesis may differ with
rice varieties.
The temperaturephotosynthesis curve of rice plants is considerably affected
by oxgen concentration Akita (unpublished), using intact leaves of riee seedlings
grown at different nitrogen levels. observed temperature-photosy=nthesis
relations in 21% oxygen and tixyqgen-free air. Figure l shows that at leaf temperature
above l5°C_ the photosynthesis ofriee leaves in 21% oxygen is alwayts
less than that in tixygen-free air. The photorespiration, which is expressed by the
differences in photosynthetic rates between oxy-‘gen free air and 21% oxygen,
increases considerably with increasing leaf temperature. From this. the wide
temperature optimum for photosynthesis of riee plants in previous reports may
be mainly attributable to the increase in photorespiration at high temperature.
The optimum temperature for photosynthesis of rice leaves in 21% osjvgen
ranges from 25° to 30°C. When the photorespiration is controlled by oxyjgen-free
air. the optimum temperature for photosynthesis becomes a little higher in the
rice plant grown at high nitrogen level. while it does not change at a low nitrogen
level.