Abstract: Physiological responses to high temperature stress of the thalli of Pyropia dentata, P. haitanensis and P. crispata, which were commonly distributed in South China, were studied by measuring the content of chlorophyll a, carotenoids, phycoerythrin and phycocyanin, the yield of photochemical efficiency, the capacity of total antioxidant, and the scavenging rate of diphenyl picrylhydrazyl (DPPH)radical. Results showed that the content of pigments declined due to high temperature stress, and the thalli became red, white and transparent gradually. Pyropia thallus’ photosynthetic efficiency (maximal photochemical quantum yield and actual photochemical quantum yield) decreased under high temperature stress, especially under 29℃ and 32℃. Being under high temperature stress for a long time (>3d) also resulted in decreases of total antioxidant capacity and DPPH radical scavenging rate. P. haitanensis and P. dentata began to die when they were stressed under 32℃ for three days, and P. crispata could not survive under 32℃ for six days. P. crispata had the strongest resistance to high temperature stress followed by P. dentata, while P. haitanensis was the most sensitive one. Thus, P. crispata and P. dentata had the potential and advantages in extension of cultivation in South China.

Key words: Pyropia, photosynthetic pigment, photochemical efficiency, total antioxidant capacity, DPPH radical