Effects of Temperature and Light on Growth Rate and Photosynthetic Characteristics of Sargassum horneri

The changing environmental factors exerted great influences on coastal macroalgal communities. To study the responses of the brown seaweed Sargassum horneri to temperature and light, S. horneri was cultured under three temperatures (20, 25 and 30 degrees C) and three light intensities (30, 60, and 120 mu mol photonsm(-2) s(-1)) for seven days. The growth rate, chlorophyll a (Chl a) and carotenoids (Car) contents, chlorophyll fluorescence, and photosynthetic oxygen evolution rate were measured. The results show that the highest relative growth rate (RGR), maximal electron transport rate (rETR(max)); the net photosynthetic rate (P-n) were observed at the lowest temperature (20 degrees C) and highest light intensity (120 mu mol photons m(-2) s(-1)); and the RGR and P-n were significantly inhibited by the highest temperature (30 degrees C), especially at the lowest light intensity (30 mu mol photons m(-2) s(-1)) (P <0.05). Additionally, the highest light intensity enhanced the non-photochemical quenching (NPQ) even under the highest temperature (30 degrees C), indicating that the higher light intensity could induce photo-protection reaction of thalli. These results suggest that the higher temperature and lower light intensity exerted negative influences on S. horneri.