Effects of the interaction between ozone and carbon dioxide on gas exchange, ascorbic acid content, and visible leaf symptoms in rice leaves
2008
Imai, K | Kobori, K
Tropospheric ozone (O₃) decreases photosynthesis, growth, and yield of crop plants, while elevated carbon dioxide (CO₂) has the opposite effect. The net photosynthetic rate (P N), dark respiration rate (R D), and ascorbic acid content of rice leaves were examined under combinations of O₃ (0, 0.1, or 0.3 cm³ m⁻³, expressed as O⁰, O⁰.¹, O⁰.³, respectively) and CO₂ (400 or 800 cm³ m⁻³, expressed as C⁴⁰⁰ or C⁸⁰⁰, respectively). The P N declined immediately after O₃ fumigation, and was larger under O⁰.³ than under O⁰.¹. When C⁸⁰⁰ was combined with the O₃, P N was unaffected by O⁰.¹ and there was an approximately 20 % decrease when the rice leaves were exposed to O⁰.³ for 3 h. The depression of stomatal conductance (g s) observed under O⁰.¹ was accelerated by C⁸⁰⁰, and that under O⁰.³ did not change because the decline under O⁰.³ was too large. Excluding the stomatal effect, the mesophyll P N was suppressed only by O⁰.³, but was substantially ameliorated when C⁸⁰⁰ was combined. Ozone fumigation boosted the R D value, whereas C⁸⁰⁰ suppressed it. An appreciable reduction of ascorbic acid occurred when the leaves were fumigated with O⁰.³, but the reduction was partially ameliorated by C⁸⁰⁰. The degree of visible leaf symptoms coincided with the effect of the interaction between O₃ and CO₂ on P N. The amelioration of O₃ injury by elevated CO₂ was largely attributed to the restriction of O₃ intake by the leaves with stomatal closure, and partly to the maintenance of the scavenge system for reactive oxygen species that entered the leaf mesophyll, as well as the promotion of the P N.
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