Comparison Study on Photosynthesis of Pagoda Tree and Walnut Seedlings under Salinity

Photosynthesis of half year seedlings of pagoda tree and walnut were determined after different time treatment of 50,100 and 200 mmol·L-1 NaCl. Results showed that photosynthetic rate of walnut decreased distinctly and decreased more when the salinity increased and treatment time lengthened. Photosynthetic rate of pagoda tree increased after salt treatment and increment was less when treatment time lengthened. The content of chlorophyll a and b of both tree species changed little during 24 stressed days of 200 mmol·L-1 NaCl with the exception of ratio of chlorophyll a to b reduction in walnut. The content of xanthophyll in pagoda tree increased firstly and then kept the level as that of the control. In contrast to pagoda tree, the content of xanthophyll in walnut decreased obviously. Main difference between pagoda tree and walnut in CO2 response curves was that photorespiratory rate in pagoda tree decreased to 43.7% of the control with 71.6% of the control increase in walnut and that CO2 compensation point decreased 13.58% in pagoda tree with 194.15% increase in walnut both compared to the control. Light response curves revealed that dark respiratory rate of pagoda tree was 3 folds more than that of the control while that of walnut decreased to 65.28% of the control. And photo inhibition occurred in salt stressed walnut.