Elevated atmospheric CO2 mitigated photoinhibition in a tropical tree species, Gmelina arborea

Effects of elevated CO2 on photosynthetic CO2 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 CO2 had a significant effect on CO2 assimilation rates and maximal efficiency of PSII photochemistry. Chlorophyll a fluorescence induction kinetics were measured to determine the influence of elevated CO2 on PSII efficiency. During midday, elevated CO2-grown Gmelina showed significantly higher net photosynthesis (p < 0.001) and greater FV/FM (p < 0.001) than those grown under ambient CO2. The impact of elevated CO2 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 CO2 compared to ambient CO2-grown plants. Our results clearly demonstrate that decreased susceptibility to photoinhibition in elevated CO2 grown plants was associated with increased accumulation of active PSII reaction centers and efficient photochemical quenching. We conclude that elevated CO2 treatment resulted in easy diminution of midday photosynthetic depression.