Comparison of Photosynthesis in Seedlings of Different Toona sinensis Provenances

The seasonal and daily changes of photosynthesis and its relation with the factors of surroundings were studied in potted one-year-old seedlings of six Toona sinensis provenances from Nanjing of Jiangsu,Guangyuan of Sichuan,Dongkou of Hunan,Suizhou of Hubei,Xixia of Henan and Ankang of Shanxi.The results showed that the seasonal changes of the net photosynthetic rate(Pn) were similar for six provenances.In May and June they were low and increased gradually,and reached to peak in July,but then sharply decreased to very low in August.In September the Pn increased greatly and reached to its secondary peak.The daily changes of Pn were unsymmetrical two-peak curves.The first peaks appeared at eight o'clock in Suizhou and Nanjing provenances,and the others were at ten o'clock.The secondary peaks were all appeared at two o'clock in the afternoon.This indicated an obvious the mid-day depression of photosynthesis regulated by stomatic and non-stomatic factors doubly.There were significant differences(P 0.001)in photosynthetic parameters of Pn,transpiration rate(Tr),stomatic conductance(Gs),intercellular CO2 concentration(Ci) and water use efficiency(WUE) among six provenances.Correlation analysis showed that Pn was significantly positive correlation to Tr and WUE(P 0.05),and extremely significant positive correlation to Gs(P 0.01).However there was no significant correlation between Pn and Ci(P 0.01).