Vergara - 1976 - Physiological and morphological adaptability of ri

212 curt-tars AND RICE
EFFECTS 0F CO, ON
PHOTOSYNTHESIS. GROWTH. AND YIELD
Effects of CO, on photosynthesis of single leaves depends on irradiance and
temperature. This interaction seems to be universal among different plant species
(Hill and Whittingham, 1955; Gaastra. 1963; Brun and Cooper. 1967; Akita ct
al.. 1969'. Harper ct al., 1973). Within usually encountered ranges of temperature
and iiradiance, increasing CO, concentration in an atmosphere above 300 ppm
increases the leaf photosynthetic rate ofrnany plant species (Rabinott-‘itch. 1951;
Yamada el al., 1955'. Gaastra, 1959', Btun and Cooper, 1967', Ford and Thome,
1967). An early study showed that the rice leaf photosynthetic rate increases with
increasing CO, concentration up to about 500 ppm. above which the leaf photosynthetic
rate remains the same (Yamada et al., 1955). At high temperatures,
however, there is no sign of CO, saturation at 500 ppm even under a low light
intensity (Akita et al., 1969). An increased leaf photosynthetic rate at a high C0,
level results in increased growth and hence increases grain yield (Matsushirna
et al., 1951; Murata. 1962; Cooper and Brun. 1967; Ford and Thome, 1967'.
Riley and Hodges. 1969; Cock and Yoshida, 1973: Yoshida, 1973). Working on
yroung rice seedlings. Murata (1962) found that the relative growth rate at 1.000
ppm CO, increased 2.5 times over that at 300 ppm C0,.
Effects ofC0, enrichment on rice yield have been studied in plastic enclosures
in the field (Matsushima et al., 1961'. Cock and Yoshida. I973: Yoshida, I973).
in naturally lighted cabinets (Matsushima et a1.. 1961) and in an enclosed
inflated plastic greenhouse (Riley and Hodges, 1969). Among these, Riley! and
Ilodges made an extensive study of CO, enrichment on many grain crops. 1n
their study (personal communication), rice yfield was increased from 10.0 l/ha
at 300 ppm C0,. to 18.9 tfha at 2,400 ppm C0, when harvest was made from an
interior area. On the other hand, when the data were taken from a border area,
the yields were 13.4 t/ha at 300 ppm C0,, 25.3 tfha at 1.200 ppm C0,, and 21.2
t/ha at 2,400 ppm C0, (Table 1). Differential responses to C0, between interior
and border areas could be attributed to ventilation of CO, to the plants. In other
words. actual CO, concentration to which the plants in the border area were
exposed must have been close to or almost identical with specified CO, concentrations.
In the interior area. however. the actual C0, concentration must have
Table 1. Effects ol CO, enrichment on yield and yield components of 1R8 grown in an
enclosed inflated plastlc greenhouse. Results are expressed as relative to 300 ppm in the
interior area ‘i
Interior
Border
300 ppm 1200 ppm 2400 ppm 300 ppm 1200 ppm 2400 ppm
Pantcle [no.lm-') 1 0O 1.78 1 93 1.59 2.56 2.19
Grain tnolpanicle} 100 0.87 1.05 0.94 1.06 1.08
Grain (net/ml) 1.00 1.55 2.03 1.49 2 72 2 3?
1.000 grain 1.00 0 94 0.94 0.90 0.94 0.90
Grain yield (tlha) 100-"- 145 1.89 1.34 2.53 2.12
1 Riley and Hodges (1969). PActuaI yield was 10.0 t/na.