Seasonal variation of photosynthetic capacity in Sargassum horneri

摘要

Photosynthesis on a dry weight basis was measured with a differential gas-volumeter in Sargassum horneri to see its seasonal changes. Photosynthetic activity in leaves of S. horneri showed two peaks a year, one in November and the other in March. The seasonal pattern of photosynthesis was similar to that reported for growth of this species. Net photosynthetic rates of the upper leaves were higher than those of the lower leaves in all months except June, when the plants became mature. In June, net photosynthetic rate in the lower leaves was higher than that in the upper ones. An adaptive shift of net photosynthetic response to temperature was observed with a decline in seawater temperature from July to December. Besides temperature, growth stage and nutrient conditions in the sea also accounted for considerable seasonal photosynthetic variability.