Physiological differences in the growth of Sargassum horneri between the germling and adult stages

The effects of temperature, irradiance, and daylength on Sargassum horneri growth were examined at the germling and adult stages to discern their physiological differences. Temperature-irradiance (10, 15, 20, 25, 30A degrees C x 20, 40, 80 mu mol photons m(-2)s(-1)) and daylength (8, 12, 16, 24 h) experiments were carried out. The germlings and blades of S. horneri grew over a wide range of temperatures (10-25A degrees C), irradiances (20-80 mu mol photons m(-2)s(-1)), and daylengths (8-24 h). At the optimal growth conditions, the relative growth rates (RGR) of the germlings were 21% day(-1) (25A degrees C, 20 mu mol photons m(-2)s(-1)) and 13% day(-1) (8 h daylength). In contrast, the RGRs of the blade weights were 4% day(-1) (15A degrees C, 20 mu mol photons m(-2)s(-1)) and 5% day(-1) (12 h daylength). Negative growth rates were found at 20 mu mol photons m(-2)s(-1) of 20A degrees C and 25A degrees C treatments after 12 days. This phenomenon coincides with the necrosis of S. horneri blades in field populations. In conclusion, we found physiological differences between S. horneri germlings and adults with respect to daylength and temperature optima. The growth of S. horneri germlings could be enhanced at 25A degrees C, 20 mu mol photons m(-2)s(-1), and 8 h daylength for construction of Sargassum beds and restoration of barren areas.