Vergara - 1976 - Physiological and morphological adaptability of ri

mason‘ DIOXIDE tom RICE YIELD 213
Pumcles t no! plant 1
60
50w vmtllollofl
0 l t t
O 500 I000 I500 2000
CO2 level t ppm]
l. Etfcct of ventilation rate on paniclc number per plant
of IRS grown in an enclosed plastic greenhouse (Riley
and Hodges. 1969).
been much lower than the specified CO; concentration due to poor ventilation.
In a separate experiment by the same authors (1969). at low C0; concentrations
high ventilation produced more particles than did low ventilation. suggesting
that the transfer of CO, to the leaf was limiting panicle number at lo\v ventilation
(Fig. l). At 1.500 ppm CO1. however, a low and high ventilation produced
about the same number of panicles. This may suggest that CO1 was no longer a
limiting factor in panicle formation. Presumably. the transfer of CO, to the leaf
was increased by the increased concentration gradient. Taken together with
other data. this seems to indicate that tl1e optimum CO1 concentration for
growth and yield of rice lies between 1.500 and 2.000 ppm C0,. Analysis of
yield components in this experiment indicates that the effect of CO1 enrichment
in increasing rice yield svas almost exclusively attributed to increased panicle
number per square meter. and hence to increased grain number per square
meter. The relationship between CO; and ventilation demonstrated by Riley and
Hodges should carefully’ be taken into account when the results obtained from
enclosed environment experiments such as glasshouses. plastic houses. and
phytotron are examined. High plant densities would create large differences in
CO, concentrations at different locations of the closed environment. This would
in turn become a serious source of uneven growth. which might incorrectly be
taken as effects ofthe treatment.
CO, DYNAMICS IN FIELD PHOTOSYNTHESIS
Carbon dioxide concentration in the atmosphere varies with location. time of
day. season. and year. This vaanation is usually within a range ivf300 to 320 ppm.
In a highly industrialized country like Japan. CO, concentrations as high as 340