Abstract:In this paper, Sargassum thunbergii, Nitzschia, Ulva lactuca, and Callithamnion corymbosum were used as the experimental species to determine the influence of different light qualities (white, blue, and red light), medical treatments (1% ammonium nitrate, 3% ammonium sulfate, and 1% citric acid), and freshwater immersion on their photosynthetic efficiencies. The effectiveness of various harmful algae removal methods which are harmless to young sporophytes of S. thunbergii, were also discussed. The results showed that: for RGR (relative growth rate), Pn (apparent photosynthetic rate), and Pn/R (the ratio of apparent photosynthetic rate and respiratory oxygen consumption rate), S. thunbergii under blue light were significantly larger than those under white and red light. In comparison, Pn of Nitzschia reached its peak under the red light. The Pn of S. thunbergii and Nitzschia under blue light was significantly higher than that under white and red light, indicating that S. thunbergii outcompetes Nitzschia under blue light. Irreversible injury appeared when young sporophytes of S. thumbergii were exposed to ammonium nitrate, ammonium sulfate, and citric acid. These chemical treatments also inhibited the growth of C. corymbosum, but the effects were not significant on newborn branches of S. thunbergii and U. lactuca. Freshwater treatment caused harm to S. thumbergii young sporophytes and C. corymbosum, but there was little negative effect on U. lactuca, and newborn branches of S. thunbergii. These results suggest that in the early stages of S. thunbergii cultivation, increasing the irradiation of blue light or reducing the irradiation of red light to a certain extent, can promote the growth of S. thunbergii, and inhibit the growth of Nitzschia. The use of ammonium nitrate, ammonium sulfate, and citric acid should be avoided in the removal of unwanted algae from young sporelings of S. thunbergii. While it is not advisable to use fresh water during the early stages, a fresh water soak for half an hour can remove the unwanted algae and causes no harm to the newborn branches of S. thunbergii.
