Physiological ecology of Porphyra sporophytes: growth, photosynthesis, respiration and pigments

Growth, photosynthesis, respiration and photosynthetic pigments o f the sporophytic stage for Alaskan Porphyra species were investigated in response to various environmental variables. Optimal conchocelis growth (7.6% volume increase d ' 1) o f P. abbottae (Pa) occurred at 11°C, 80 //mol photons m"2 s ' 1 and 30ppt salinity. Porphyra torta (Pt) grew best (6.5% d ' 1) at 15°C, 80 //mol photons m"2 s_I and 30ppt. Porphyrapseudolinearis (Pi) generally had higher growth rates with optimal growth (8.8% d ' 1) occurring at 7°C, 160 //mol photons m '2 s ' 1 and 30ppt. Salinities between 20 and 40ppt and irradiances between 20 and 160 //mol photons m '2 s ' 1 generally had little effect on growth rates, but there was virtually no growth at <10ppt. Plant hormones were shown to promote the growth o f conchosporangia, which increased by 6.9-31.7% (for Pa), 4.7-25.7% for (Pe, P. pseudolanceolata) and 8.9-35.1 % for (Pi). Concentrations between 0.4-1.6ppm o f kinetin and indole-3-acetic acid at higher temperatures generally had higher stimulatory effects, but Pe had higher volume increase at lower