Photosynthetic and respiratory responses of Gracilaria salicornia (C. Ag.) Dawson (Gracilariales, Rhodophyta) from Thailand and Japan

摘要

The photosynthetic and respiratory responses of Gracilaria salicornia in the subtropical waters of Japan (in Okinawa) and in the tropical waters of Thailand (in Rayong and Phuket Provinces), were studied under various conditions of irradiance, salinity and temperature. This alga showed adaptability in its photosynthetic and respiratory responses to oceanic salinity as well as to subtropical to tropical temperature. Significant differences in the photosynthetic and respiratory rates among the G. salicornia populations collected from the above sites were observed. The Phuket population showed adaptability to high irradiance and temperature, characteristic of its natural sun-exposed environment, as it exhibited the highest I k and I c, and lowest l and higher P max at 30-35pC. On the other hand, the Okinawa population demonstrated adaptability to low submarine irradiance as it had a lower I k and I c than either population from Thailand. Its P max at 20-25pC was also higher than that of the Phuket population. The Rayong population, however, showed the highest P max, Rd, l, I k and I c, suggesting its adaptability to both sun and shade light conditions in its natural environment.