Abstract: Net photosynthetic rate(Pn) and apparent quantum yield(AQY) were measured with Li-6200 portable photosynthesis system in parallel with superoxide dismutase(SOD) activity determined with UV-754 ultraviolet spectrophotometer in attached leaves of poplar clone seedlings. It was found that Pn decreased, and photosynthesis depression phenomenon occurred at noon. At this conditions Pn was limited by non-stomatal factors, and the decline of Pn had no relations with the closure of stomata. AQY in attached leaves of poplar clone seedlings decreased and photoinhibition of photosynthesis occurred evidently under stressful conditions. SOD could protect photosynthesis. The inhibitor of SOD could intensified, while antioxidant could alleviated, photoinhibition of photosynthesis. The conclusion was that photoinhibition of photosynthesis in attached leaves of poplar clone seedlings had intrinsic relations with the accumulation of reactive oxygen species.

Key words: Poplar clone, Photosynthesis, Photoinhibition of photosynthesis, Reactive oxygen species