Vergara - 1976 - Physiological and morphological adaptability of ri

196 ems-tars AND RICE
of tillers had an inverse proportion to stem elongation (plant height). and the
optimum temperature for stem elongation was about 25°—30°C. This optimum
range is equal to thc intermediate of two optima for the number ofpanicles.
These results suggest that inhibition of stem elongation at low and high
temperatures brought about the increase of tillers, resulting in the temperature
curve with two optima for the number ofpanieles and spikelets.
Iloshino et a]. (1971) observed that the optimum temperature for the height
of rice seedlings became lower with increased amounts of nitrogen applied
to soil. From these results, it seems likely that the temperature curve with two
optima is attributable to the increase in ammonification of soil by high temperature,
as Well as by the inhibition of stem elongation at low and high temperatures.
Figure 8 indicates schematically such relationships among temperature. stem
elongation, panicle (or spikelet) production. and ammonification in soil.
The relationships between sunshine hour (s) and number of spikelets (Y3)
can also be read from Fig. 5A and 5B.
The light saturation point of Y; seems to be at about 8 hours of sunshine at
[~40] stage and at about 6 hours at [-20] stage. This suggests that the effect of
strong solar radiation is a little less at [-20] than at [-40] stage. Such a tendency
agrees with the result in standard partial regression coefficients 011 the
stinshine hours (b3) in Fig. 4.
Relotive vtJlue
Anvnolifieutbn in soil
Nunber of punicles
Ternoeroture (°Cl
8. Schematic relationships among temperature response
curves of plant height, ammonifieation in soil. and number
of panicles.