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

Abstract

Growth, photosynthesis, respiration and photosynthetic pigments of the sporophytic stage for Alaskan Porphyra species were investigated in response to various environmental variables. Optimal conchocelis growth (7.6%) volume increase d⁻¹) of P. abbottae (Pa) occurred at 11C̊, 80 umol photons m⁻² s⁻¹ and 30ppt salinity. Porphyra torta (Pt) grew best (6.5%d⁻¹) at 15C̊, 80 umol photons m⁻² s⁻¹ and 30ppt. Porphyra pseudolinearis (Pi) generally had higher growth rates with optimal growth (8.8% d⁻¹) occurring at 7C̊, 160 umol photons m⁻² s⁻¹ and 30ppt. Salinities between 20 and 40ppt and irradiances between 20 and 40ppt and irradiances between 20 and 160 umol 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 of 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 of kinetin and indole-3-acetic acid at higher temperatures generally had higher stimulatory effects, but Pe had higher volume increase at lower temperatures. Irradiance, temperature and salinity influenced photosynthesis of the conchocelis. P-I curves, Pmax, Imax, and Ic varied with temperature and species. Higher photosynthesis generally occurred at 25-35ppt salinities. Pa had maximal photosynthesis at 11C̊ and 60 umol photons m⁻² s⁻¹, whereas Pi and Pt had maximal photosynthesis at higher temperatures and irradiances. The highest photosynthesis (240 umol O₂ production g dw⁻¹ h⁻¹) of Pa occurred at 11C̊, 60umol photons m⁻² s⁻¹ and 30ppt. Pi and Pt had optimal photosynthetic rates (200 and 210, respectively) at 15C̊, 120 umol photons m⁻2 s⁻¹ and 30ppt. Conchocelis had lower respiration rates (30-35) at 7C̊ than at 11 and 15C̊ (45-58 umol O₂ consumption g dw⁻¹ h⁻¹). All three species exhibited lowest respiration at salinities between 25-35ppt. Phycoerythrin (PE), phycocyanin (PC), carotenoid Ca) and chlorophyll a (Chl.a) contents were significantly affected by irradiance, nutrient concentration and culture duration. For Pa, Pi and Pt, maximal PE (63.2-95.1 mg/g.dw) and PC content (28.8-64.8 mg/g.dw) generally occurred at 10 umol photons m⁻² s⁻¹, f/4-f/2 nutrient concentration after 10-20 days, while Pe had highest PE (73.3 mg/g.dw) and PC content (70.2 mg/g.dw) at 10 umol photons m⁻² s⁻¹, f nutrient concentration after 60 days. For all four species, highest Ca (3.4 - 6.3) and Chl.a content (3.6 - 8.1 mg/g.dw) generally occurred at 0-10 umol photons m⁻² s⁻¹, f/4-f nutrient concentration. High irradiances, low nutrients and longer culture duration generally caused a decline of pigment content.