Abstract
Effects of elevated CO 2 on photosynthetic CO 2 assimilation, PSII photochemistry and photoinhibition were investigated in the leaves of a fast growing tropical tree species, Gmelina arborea ( Verbenaceae) during summer days of peak growth season under natural light. Elevated CO 2 had a significant effect on CO 2 assimilation rates and maximal efficiency of PSII photochemistry. Chlorophyll a fluorescence induction kinetics were measured to determine the influence of elevated CO 2 on PSII efficiency. During midday, elevated CO 2-grown Gmelina showed significantly higher net photosynthesis ( p < 0.001) and greater F V/ F M ( p < 0.001) than those grown under ambient CO 2. The impact of elevated CO 2 on photosynthetic rates and Chl a fluorescence were more pronounced during midday depression where the impact of high irradiance decreased in plants grown under elevated CO 2 compared to ambient CO 2-grown plants. Our results clearly demonstrate that decreased susceptibility to photoinhibition in elevated CO 2 grown plants was associated with increased accumulation of active PSII reaction centers and efficient photochemical quenching. We conclude that elevated CO 2 treatment resulted in easy diminution of midday photosynthetic depression.
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