Growth performance of unialgal gametophytes of the brown alga Saccharina japonica in mass culture conditions

For the purpose of mass culture of Saccharina japonica unialgal gametophytes originated from spores in laboratory conditions to breed sporelings, a series of experiments were designed to evaluate vegetative growth performance of male and female gametophytes. After 8-day culture, female gametophytes exhibited the higher relative growth rates (RGRs) around 8.29–9.27 % day−1 than male ones (5.30–6.10 % day−1). Both male and female gametophytes had the higher RGRs in NO3 −-supplemented medium than that in NH4 + medium under equal nitrogen concentration. The RGRs of the female and male could reach the peak levels of 8.96 and 5.91 % day−1 in NO3 − group and 6.60 and 3.89 % day−1 in NH4 + group, respectively. Elevation of temperature from 5 to 15 °C significantly promoted the vegetative growth of both in the medium enriched with 450 μM of NO3 − or NH4 +. At higher temperature (25 °C), the growth rates of both were retarded greatly with the female being more sensitive to the exposure to 450 μM of NH4 +, and the photosynthesis activity was partially damaged as reflected by the decrease of the optimal chlorophyll fluroscence quantum yield (Fv/Fm) from 0.657 ± 0.023 to 0.401 ± 0.053.