Abstract:The effect of salinity and Na3VO4 on photosynthesis of Bangia fuscopurpurea and Bangia atropurpurea was investigated, respectively, to investigate the photosynthetic physiology of Bangia, using chorophyll Ⅱ fluorescence and photosynthetic oxygen evolution measurements. The main results were as follows: The conversion efficiency of primary light energy of PSⅡ (Fv/Fm) of B. fuscopurpurea declined rapidly in salinity conditions lower than natural seawater while that of B. atropurpurea declined in salinity higher than freshwater, and the decrease was positively related to the level of stress. The Fv/Fm of B. fuscopurpurea was significantly inhibited under salinity 0 and 8 after 3 days of hyposaline treatment. No significant difference was seen among the different hyposalinity-stressed groups of B. fuscopurpurea. The Fv/Fm of B. atropurpurea under hypersaline stress was significantly lower than that of the control from the first day, and recovered to control levels after 6 or 7 days of hypersaline treatment. Saline stress had significant effects on net photosynthetic rate (Pn) in both Bangia species. Respiratory oxygen consumption rate (Rd) decreased at the early stage and then rapidly recovered to the level of the control on the first day. After 1 day, Rd of the hyposalinity-stressed B. fuscopurpurea groups was significantly lower than the control. As the hypersalinity continued, Rd of the stressed B. atropurpurea increased and became significantly higher than the control. After 3 days, the Fv/Fm of B. fuscopurpurea decreased significantly under treatment with 200~500 μmol/L Na3VO4. The decrease of Fv/Fm in B. atropurpurea with Na3VO4 treatment was positively correlated with Na3VO4 concentration. In general, with an increase in Na3VO4 concentration, the salinity stress had significant inhibitory effect on the Fv/Fm and Pn of Bangia. Rd of both B. fuscopurpurea and B. atropurpurea increased with stress, an effect that was more obvious in B. atropurpurea. The present results reveal that both marine and freshwater Bangia respond quickly to saline stress. The enhancement of Rd and regulation of plasma membrane-H+-ATPase may play an important role in response to saline stress. Long-term saline stress had irreversible harmful effects on photosynthesis in Bangia.
