Growth and metabolic responses of the tropical red alga Gracilaria blodgettii Harvey under different abiotic factors

抄録

Carposporelings of Gracilaria blodgettii Harvey were exposed to different temperature (20℃, 25℃, 30℃ and 35℃), salinity (20‰, 25‰, 30‰ and 35‰) and irradiance (60 µmol photons m^-2s^-1 and 100µmol photons m^-2s^-1) levels to determine effects on growth and photosynthetic performance using a series of factorial experiments. Growth was significantly affected by variations in temperature and irradiance levels with highest growth rates obtained at 25℃ (13.1% d^-1) and 100µmol photons m^-2s^-1 (12.7% d^-1). No significant difference was found at all salinity levels tested. Photosynthesis-irradiance (P-I) parameters were directly proportional with increasing temperature. Significantly higher net photosynthesis (Pmax) was obtained at 30℃ and 35℃ than at 25℃ and 20℃ but were complemented with higher respiration rates (1.19 for 30℃ and 1.32 for 35℃) ( p < 0.05). The high photosynthetic efficiency (α) which suggests its ability to maximize low-light conditions was also significantly higher at 25℃ to 35℃ (0.04 to 0.05) than at 20℃ ( p < 0.05). This is further shown by the low compensation point photon fluxes (Ic) (19-27µmol photons m^-2s^-1) and saturation photon fluxes (110-159µmol photons m^-2s^-1). Salinity did not produce significant differences on the photosynthetic responses of the seaweed. This study concludes good culture conditions for Gracilaria blodgettii at 25℃ and 100µmol photons m^-2s^-1 based on high growth rates and high photosynthetic rates with low respiration.