Effects of drought stress on photosynthetic characteristics in Toona sinensis seedlings from different provenances.

Effects of drought stress on photosynthesis were studied in potted Toona sinensis seedlings of six provenances, which were from Nanjing, Guangyuan, Dongkou, Suizhou, Xixia and Ankang cities. The results showed that under drought stress, the net photosynthetic rate (Pn) and stomatal conductance (Gs) decreased in leaves of six provenances, while intercellular CO2 concentration (Ci) showed different trends. With prolonged stress, the decrement of Pn fell down. The highest decrement of Pn was observed in Dongkou provenance which had less tolerance to drought stress and recovered less after rewatering. The change of Gs was similar to that of Pn. Under two stress levels, the Gs and Ci decreased with prolonged stress in provenances of Nanjing, Guangyuan, Xixia and Ankang, whose photosynthetic abilities were mainly restricted by stomatal factors. For the provenances of Dongkou and Suizhou, the Gs decreased while the Ci increased during the end period of treatment, whose photosynthetic abilities were mainly restricted by both stomatal and non-stomatal factors; the plants of these two provenances recovered slowly after rewatering. The dynamic changes of photosynthetic parameters (Pn, Gs and Ci) in six T. sinensis provenances showed the same trend with drought-resistant ability.