Vergara - 1976 - Physiological and morphological adaptability of ri

236 (‘LIA-LATE AND RICE
and C, species, and there are striking similarities in CO, responses among
species having the same photosynthetic pathvsay
C, species such as sugarcane and maize have been found to have CO, compensation
points of less than 1O ppm and a high ability to absorb CO, in lowconcentration
air. Under the same condition. C; species such as tobacco and
orchardgrass had compensation points of 6O ppm or more and low photosynthetic
capacity in low CO, environment. Takeda and Fukuyama (1971) measured
CO, compensation points in many species of Grcmzineaie and found that thc
CO; compensation points showed 27-37 ppm CO, in Bambosoirleae, Orjvzoideae,
IIHIHdiHOidGUQ, and Feslicoideae, and 0-4 ppm CO; in Elragrosreae, Chforirfeae,
Zoysiezre, Arimdinelieae, Panic-sac, and xlnrlropogoneue. Although CO, compensation
points vary depending upon such factors as temperature. light intensity.
and nitrogen content, the general relation between two groups of plants
remains similar. The fact that C, species are better adapted to low CO, environment
is shown by Menz et a]. (1969). They obsened that when a mixture of C,
and C, species was grown together in a11 enclosed chamber xvith illumination, C.
species having a low CO3 compensation point (near zero ppm) could survive
longer than C, species having a high CO, compensation point.
The CO; saturation point for photosynthesis differs with species having
different photosynthetic pathways. Akita a11d Tanaka ( 1973b) reported that
the photosynthesis of C, species such as rice. wild rice. sunflower, and cucumber,
increased progressively with increasing CO, in the air and did not reach
saturation even at 1.500 ppm C0,, while the photosynthesis of C, species such as
barnyardgrass. maize. (ii/penis serotimis, and Amaranrhus pom/us became
saturated at about 1,000 ppm CO1, and the efrect of CO1 enrichment on photosynthesis
was relatively smaller. The increased rate of photosynthesis by CO,
enrichment. as expressed by the ratio of the photosynthesis in 1,000 ppm CO,
to that in 300 ppm C0,. was 54-75% in C, species while it was only 12-27% in
C, species (Table 2).
Transpiration also is influenced by CO, concentration in the air. and the CO,
response differs between C. and C, species. Pallas (1965) reported that complete
stomatal closure ofC. species such as maize and sorghum occurred in 02-03%
CO1, while C, species such as soybean and tomato did not close completely even
in 0.4% C0,. Akita and Moss (1972) reported that stomata of C, species were
less prone to close than were stomata of C, species as the CO2 concentration
was increased. The ratio of transpiration to photosynthesis in C, species was
higher than that in C, species. especially) in 300 ppm CO1 (Akita and Tanaku,
1973b).
When the photorespiration ofC, species was diminished by lowering oxygen.
the COz-photosynlhesis curve became saturated at a lower CO1 concentration.
similar to that in C, species (Goldsuiorthyi, 1968; Akita and Miyasaka. 1969).
If the diffusion resistance of stomata were supposed to be the same in these
species, the difference 111 the CQ-photosyjnthesis curve in low O, concentration
between the two would be much smaller (Akita et al., 197]). Thus, the differen-