Elevated CO(2) Concentration Alters Photosynthetic Performances under Fluctuating Light in Arabidopsis thaliana

In view of the current and expected future rise in atmospheric CO(2) concentrations, we examined the effect of elevated CO(2) on photoinhibition of photosystem I (PSI) under fluctuating light in Arabidopsis thaliana. At 400 ppm CO(2), PSI showed a transient over-reduction within the first 30 s after transition from dark to actinic light. Under the same CO(2) conditions, PSI was highly reduced after a transition from low to high light for 20 s. However, such PSI over-reduction greatly decreased when measured in 800 ppm CO(2), indicating that elevated atmospheric CO(2) facilitates the rapid oxidation of PSI under fluctuating light. Furthermore, after fluctuating light treatment, residual PSI activity was significantly higher in 800 ppm CO(2) than in 400 ppm CO(2), suggesting that elevated atmospheric CO(2) mitigates PSI photoinhibition under fluctuating light. We further demonstrate that elevated CO(2) does not affect PSI activity under fluctuating light via changes in non-photochemical quenching or cyclic electron transport, but rather from a rapid electron sink driven by CO(2) fixation. Therefore, elevated CO(2) mitigates PSI photoinhibition under fluctuating light at the acceptor rather than the donor side. Taken together, these observations indicate that elevated atmospheric CO(2) can have large effects on thylakoid reactions under fluctuating light.