Impact of Environmental Factors on the Photosynthesis and Respiration of Young Seedlings of <i>Sargassum thunbergii</i> (Sargassaceae, Phaeophyta)

Abstract

Sargassum thunbergii is of great economic and ecological value to sea cucumber cultures and seaweed beds. However, studies on photosynthesis and respiration of S . thunbergii are limited. In this study, a liquid-phase oxygen electrode system and a chlorophyll fluorescence spectrometer were used to determine the photosynthetic characteristics of S . thunbergii seedlings at various light intensities, temperatures, and salinities. The light-saturated net photosynthetic rates, light saturation points, and respiratory rates of germlings were investigated. Results showed that the increase in rate of light saturation point was slow in the first 4 d, rapidly increased from 5 d to 9 d, and then gently increased at the final few days of the 15 d indoor culture period. The photosynthetic rate or respiratory rate of the seedlings rapidly and significantly decreased when the temperature was <10 ° C or >28 ° C . Short-term high- or low-salinity shock had significant effect on the photosynthetic and respiratory rates of the seedlings, specifically at 10 and 50 psu. However, the photosynthetic and respiratory rates recovered to the normal levels after 24 h of recovery period, which demonstrated a powerful ion-transport system of the seedlings. These results provided reference for the artificial breeding of S . thunbergii .