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Net photosynthetic rate (mmol m –2 s –1 )
40
Exposure to O 3
and/or CO 2
O 3
-free air
35
30
25
20
15
10
5
0
Stomatal conductance (mmol m –2 s –1 )
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0 4 7 11 14 18 21
Days of treatment
Fig. 2. Effects of O 3 and CO 2 concentrations on net photosynthetic rate and stomatal conductance
at vegetative growth stage (experiment 1, long-term; 1-4).
= 0 ppm O 3 + 400 ppm CO 2 plot, = 0.1 ppm O 3 + 400 ppm CO 2 plot,
= 0.1 ppm O 3 + 800 ppm CO 2 plot, = 0 ppm O 3 + 800 ppm CO 2 plot.
vegetative growth stage, the main reason could be a decline in
stomatal conductance (in other words, stomatal closure) induced
by elevated CO 2 , which suppressed the invasion of O 3
inside the leaf cavity as a physical barrier. The O 3 effect on
yield could be attributed to an increase in infertile caryopses
at lower positions of the rachis branch of the panicle because
of a decline in photoassimilate accumulation. Further investigations
should be done for the light environment, plant age,
and biochemical reactions in treatments to understand the interaction
of O 3 and CO 2 in lowland rice.
References
Imai K, Coleman DF, Yanagisawa T. 1985. Increase in atmospheric
partial pressure of carbon dioxide and growth and yield of
rice (Oryza sativa L.). Jpn. J. Crop Sci. 54:413-418.
Ishioh T, Imai K. 2003. Effects of atmospheric ozone and carbon
dioxide concentrations on growth and yield of lowland rice.
Jpn. J. Crop Sci. 72(Suppl. 2):286-287. (In Japanese.)
Ishioh T, Imai K. 2004. Interaction between ozone and carbon dioxide
on gas exchanges in leaves of lowland rice. Jpn. J. Crop
Sci. 73(Suppl. 2):240-241. (In Japanese.)
Session 19: Climate change and rice production 559