Vergara - 1976 - Physiological and morphological adaptability of ri

238 ensure AND rues
tial response of photosynthesis between C, and C, species to CO, concentration
was mainly attributed to the difference in the photorespiration and diffusion
resistance of stomata.
The effect of CO, enrichment of the air on growth differs with C, and C,
species. Akita and Tanaka (l973b). using l6 C, species (summer plants and
whiter plants) and 15 C, species (summer plants). measured the effect of CO,
enrichment. These plants were treated with CO, concentration of 300 ppm.
1.000 ppm. and 2,000 ppm (or 2.500 ppm) in the assimilation chambers for l8-
30 days in summer. In C, species. the total dry weights in 1.000 ppm and 2.000
ppm (or 2.500 ppm) xvere 1.4-4.7 times those in 300 ppm. while there were little
differences among the CO, treatments in C, species. Among C, species. the
effect of CO, enrichment was greater in winter plants than in summer plants.
Also, the effect of CO, enrichment in rice varieties was 1.8-2.6 times greater
than in the control. Such a remarkable difference in the CO, response between
C, and C, species would primarily be attributable to the differences in the CO,
response of photosynthesis between the two. The secondary cause for such a
difference seems to be temperature. Lundegardh (1927) indicated that the effect
of atmospheric CO, enrichment on photosynthesis of potato (C, species) was
greater at a higher temperature, because the optimum temperature for photosynthesis
was raised by the increase of CO, concentration. Akita et al. (1969)
found that the optimum temperature for photosynthesis of C, species was
scarcely affected by CO, concentration. The difference in CO, response of
growth between C, and C, species may be attributed to these CQ-tcmperaturephotosynthesis
relations.
Oxygen response of photosytnthesis and growth of rice
C, species such as rice and wheat have a CO, release in light, that is photorespiration.
which has been linked to glycolate metabolism (Zelitch. 1966) and with the
presence of cell organelles called peroxisomcs (Tolbcrt ct all. 1969). C, species
such as maize and sugarcane do not photorespire. Photorespiration increased
proportionally to the increase of oxygen. and consequently the CO, uptake of
C, species was greatly influenced by oxygen concentration (Forrester et al.,
1966). There is much evidence that photosynthesis and dry matter production of
C, species are increased remarkably by low tixygen concentration in the air.
However. the drastic change in tixygen concentration from 21% to a very low
level may inhibit some of the physiological functions of higher plants which have
adapted to the present atmosphere.
The effect of low oxygen concentration for a long period on dry matter production
and growth of rice was reported by Akita and Tanaka (1973b). The
plants were treated in assimilation chambers aerated with oxygen concentration
of2l% and 3% only in daytime for 20 days from heading time to milky-dough
stage. The increased dry weight in 3% taxygen was 54% greater than in 21%
orwgen. This increase was mainly’ due to reduced pliotorespiration through lob
oxygen concentration, because the photosynthetic capacity in a normal air just