Photosynthetic response of <Emphasis Type="Italic">Bangia fuscopurpurea</Emphasis> (Bangiales,Rhodophyta) towards dehydration and hyposalinity

Bangia fuscopurpurea, an important farmed species in China, inhabits upper intertidal zones where it suffers periodical desiccation and salinity stress. However, the physiological response and acclimation mechanism of Bangia to abiotic stress is unknown. Here, the photosynthetic response of B. fuscopurpurea to desiccation and hyposalinity was investigated by using chlorophyll fluorescence measurement. The optimum photosynthetic efficiency of photosystem II (Fv/Fm), photochemical quenching (qP) and the non-photochemical quenching (NPQ) of B. fuscopurpurea thalli maintained at basal level when the absolute water content (AWC) was 32%. As AWC decreased from 32% to 9%, Fv/Fm dropped from 0.62 to 0.1 and NPQ increased from 0.2 to 1.2. No significant change occurred in the mean qP but great standard deviation was present as AWC was 9%. Fv/Fm, qP and NPQ of the thalli with 9% AWC fully recovered after rehydration. That B. fuscopurpurea kept high photosystem II photochemical reactions even when AWC was mere 32% enabled this species to survive extreme air drying at low tide. Fv/Fm and qP dropped while NPQ increased with 1 h of varying hyposaline treatment and they regained the basal levels after 6–24 h treatment. Nine days later, Fv/Fm, qP and NPQ levels of the thalli in 100% freshwater was equal to the control level (0.62, 0.9, 0.1, respectively). The present finding suggested that this alga has high photosynthetic capacity to survive during low tide, even during heavy rainfall. We hope this study would facilitate further investigation on the stress acclimation mechanism of B. fuscopurpurea.