Effects of reduced carbon supply and sunlight on photosynthetic and antioxidant activities of Gracilariopsis lemaneiformis, and subsequent changes of these activities under recovery conditions with different salinities

Gracilariopsis lemaneiformis usually suffers reduced carbon supply and irradiance due to increasing density. Moreover, salinity also frequent changes at cultivation field. G. lemaneiformis thalli were cultured under ambient carbon (390 μatm) and decreased carbon (20 μatm) supply, with ambient sunlight and decreased sunlight conditions, and subsequent cultivation of the above four thalli under ambient carbon and sunlight with ambient (32) and low (21) salinity. The study aimed to investigate how the decreased carbon supply and sunlight conditions affected the photosynthesis and antioxidant activity, and the effects of salinity on their changes of these algae under the recovery conditions. Decreased carbon in culture reduced the maximal quantum yield of photosystem II (Fv/Fm) and non-photochemical quenching (NPQ). The Fv/Fm, NPQ, superoxide dismutase (SOD) and catalase (CAT) activity in the thalli grown at ambient sunlight condition were greater than the thalli grown at decreased sunlight. However, reduced carbon and lowered light had no synergistic inhibitory effect on photosynthetic and antioxidant activities of the algae. After the thalli were continuous cultured, the photosynthetic activity and antioxidant enzyme activity were similar between the two salinities. The results indicated that the effects of decreased carbon and sunlight on the photosynthetic and antioxidant activities of G. lemaneiformis were reversible and their recovery was also achieved under low salinity. Therefore, we suggest that it was a possible new model for G. lemaneiformis maricultivation that some algal fragments were leaved in polyethylene rope as “seeds” for the next batch of G. lemaneiformis during the algal harvest.