Photosynthetic characteristics of the economic brown seaweed Hizikia fusiforme (Sargassaceae, Phaeophyta), with special reference to its leaf and receptacle

Photosynthetic responses to irradiance and temperature of leaves and receptacles were compared in February ( vegetative stage) and May ( reproductive stage) in the seaweed, Hizikia fusiforme ( Harvey) Okamura (Sargassaceae, Phaeophyta) from Nanao Island, Shantou, China. Irradiance-saturated photosynthesis (P-max) was significantly higher in receptacles than in leaves on a fresh weight basis, and that of leaves was greater in May than in February at ambient seawater temperatures. The optimum temperature for P-max was 30 degrees C for both leaves and receptacles, being 5 - 10 degrees C higher than the ambient seawater temperature. The apparent photosynthetic efficiencies were greater in receptacles than in leaves within the tested temperature range of 10 - 40 degrees C. The irradiance for saturating photosynthesis for both leaves and receptacles was temperature-dependent, with the highest values ( about 200 mu mol photons m(-2) s(-1)) at 30 degrees C.