Abstract:The photosynthetic physiology of the different stages of the Pyropia yezoensis free-living conchocelis were investigated at different temperatures (15℃, 25℃, and 35℃) and light intensities [40, 100, and 300 μmol/(m2·s)] to reveal the regulation mechanism and establish a foundation for efficient and accurate P. yezoensis seedling technology. The main results were as follows: 1) At 15℃ and 25℃, the optimum PSⅡ quantum yield (Fv/Fm), gross photosynthesis rate (Pg), and net photosynthetic rate (Pn) of the vegetative conchocelis and conchosporangial branches decreased as light intensity increased. Fv/Fm and Pg of the vegetative conchocelis filaments dropped to zero under 300 μmol/(m2·s) light intensity, and the values of Pn were below zero. The respiratory oxygen consumption rate (Rd) of the vegetative conchocelis was significantly higher than that of the conchosporangial branches at 25℃ and 40 μmol/(m2·s). The difference in the Rd values between vegetative and conchosporangial branches decreased gradually during culturing under the other conditions. In general, Fv/Fm, Pg, and Pn of the conchosporangial branches were significantly higher than those of the vegetative conchocelis filaments and there was no significant difference in Rd between the two developmental stages under most culture conditions; 2) Fv/Fm of the conchosporangial branches was significantly higher than that of the vegetative conchocelis at 6 h of culture at 35℃, which decreased with increasing light intensities. Fv/Fm of the other treatments was nearly zero. Pg and Rd of the conchosporangial branches were higher than or equivalent to that of the vegetative conchocelis after 6 h of culture at 35℃, and 40 or 100 μmol/(m2·s). After 1 d or 2 d, Pn and Rd of the vegetative conchocelis were higher than those of the conchosporangial branches, while the Pn and Rd were all below zero under 300 μmol/(m2·s) conditions during the entire experimental period. Overall, Fv/Fm, Pg, and Pn of free-living P. yezoensis conchocelis were significantly lower (mostly zero or below), whereas Rd was higher at 35℃ than at 15℃ or 25℃. After 1~3 d, both vegetative conchocelis and conchosporangial branches became green or white. In summary, under the light intensity and temperature conditions in which the vegetative conchocelis was severely inhibited, conchosporangial branches had relatively high photosynthetic activity. The present findings indicated that high light intensity and temperature were not beneficial to vegetative conchocelis, but they could stimulate the vegetative conchocelis to turn into conchosporangial branches, and conchosporangial branches have greater resistance ability under high- temperature and light intensity stress.
