Abstract: Sargassum horneri is a key species in “golden tide”. In order to explore the reason of “golden tide”, we collected floating and benthic S. horneri at same site, and cultured at 15 ℃ and 5000 lx for 7 days, and then compared the growth rates and photosynthetic characters between the two types of S. horneri. The results showed that the relative growth rate (RGR) of floating S. horneri was 8.25%·d^-1, while that of benthic S. horneri was only 5.79%·d^-1. The photosynthetic pigment contents in leaves (old and newborn leaves) of benthic S. horneri were higher than that of floating S. horneri. Floating S. horneri had higher NPQ and Y(NPQ)values than benthic ones. Newborn leaves of both species types had higher maximum relative electron transfer rate (rETR_max) and saturation light intensity (I_k) than other tissues (old leaf, vesicle, and stem). These results indicated that there were significant differences in physiological characteristics between benthic and floatingS. horneri. Floating S. horneri had better growth ability and stronger heat dissipation ability. Newborn leave had stronger tolerance under high light. Our results suggest that the floating type was more suitable to sea surface environment.

Key words: Sargassum horneri, photosynthesis, relative growth rate, chlorophyll fluorescence.