Effects of temperature and irradiance on the growth of regenerated juveniles from Sargassum fusiforme holdfasts

To improve the quality of Sargassum fusiforme seedlings, suitable strains of juveniles regenerated from holdfasts need to be bred. In this study, effects of different temperatures (16, 20, and 24 °C) and irradiances (100, 120, and 160 µmol photons·m−2·s−1) on the growth of juveniles (new individuals) from the holdfasts of S. fusiforme were investigated to provide strategies for the cultivation of vegetative propagation seedlings of S. fusiforme. The results demonstrated that during cultivation at 24 °C, the regenerated juveniles rotted after twenty-one days, and their relative growth rate, photosynthetic activity and pigment content decreased substantially. The low temperature of 16 °C also decreased their photosynthetic activity and growth considerably. At a high irradiance of 160 µmol photons·m−2·s−1, the growth rate and photosynthetic activity decreased. Under conditions of 20 °C and 120 µmol photons·m−2·s−1, juveniles showed higher photosynthetic activity and nitrate uptake rates, which increased the growth of the juveniles and lateral branches and promoted the accumulation of photosynthetic pigment. Therefore, culture conditions of 20 °C and 120 µmol photons·m−2·s−1 can be applied for early indoor cultivation of regenerated juveniles of S. fusiforme. This study provided technical support for solving the problem of single provenance of S. fusiforme seedlings.