Light Stress Conditions The Photosynthetic Characteristics Of Strawberry

The strawberries, which are planted infield, are often affected by light. Too high or low light leads to a reduction in the rate of photosynthesis and therefore a reduction in the rate of growth .The physiological changes of strawberries under shading and photooxidition were studied in this research. 1. Five strawberry varieties were treated under shading condition and dry weight was measured . It had been found that there were some differences aniong them. Baojiaozaosheng whose dry weight decreased by 27% was considered as variety with strong shading tolerance. Shuofeng whose weight decreased by 80% was considered as variety with less shading tolerance .The physiological index of them was compared after shading treatment. The results showed that under shading condition, the net photosynthesis rate of Baojiaozaosheng decreased by 20% while that of Shuofeng decreased by 47%. However, the AQY of them was enhanced by 13%and 8%, respectively. The shading treatment did not change the response of photosynthesis rate to temperature at the two varieties, but at different temperature, the decrease of photosynthesis rate of Baojiaozaosheng under shading condition was less that that of Shuofeng . The chlorophyll content and soluble protein content were also determined. The chlorophyll content Baojiaozaosheng was enhanced by 17% while that of Shuofeng was enhanced less under shading condition. The Chla/Chlb decrease less. The soluble protein of Baojiaozaosheng decreased by 16% while that of Shuofeng decreased by 32%. The PSII activity, the key index of photochemical reaction, was also measured .The PSII activity of Baojiaozaosheng and Shuofeng decreased by 22. 5%and 53. 7% respectively under shading condition. The activity of Rubisco was determined and it was found that the Rubisco activity of the two varieties decreased by 19. 6%and 35. 3% respectively. 2. Five strawberry varieties were treated under photooxidition condition and their physiology index was measured. The results revealed that Mingbao whose chlorophyll content decreased by 69% was considered as photooxidition sensitive variety. Shuofeng whose chlorophyll content decrease by 29% was considered as photooxdition tolerant variety. The soluble protein content of Mingbao decreased by 70% while that of Shuofeng decreased by 60%. To study the physiology basis, The active oxygen of strawberry under photooxidition condition was determined. The results showed that:the 02~ and I~1202 were enhanced by l16%and 125% respectively while those of Mingbao were enhanced by 179%and 180% respectively. The activity of active oxygen scavenger including SOD, POD and CAT were determined .The results showed that under photooxidition condition SOD activity was induced to a highlight then decreased progressively. POD activity was enhanced progress while CAT activity decreased progressively under photooxidition condition. There was significant difference among them. Compared with Mingbao, the scavenger activity of Shuofeng was kept steady . The fluorescence value was also determined in order to study the photochemical efficiency under photooxdition condition .The results showed that under photooxdition condition, Fv/Fm decreased less on Shuofeng compared with Mingbao. The fluorescence quench was also determined and the results showed that Shuofeng started the xanthyll cycle intensively to clear off more energy and it was the reason that Shuofeng kept higher photochemical efficiency.