LAUSR

The chronic effects of three different stressors, irradiance, temperature, and desiccation, on Photosystem II (PSII) photochemical efficiency were investigated in two heteromorphic life-history stages of a cultivated red alga, Pyropia yezoensis f. narawaensis (Bangiales) from Japan. The maximum quantum yields of PSII (Fv/Fm) over the range of temperature between 4 and 36 °C for 96-h exposure showed different responses in the two life-history stages. In the macroscopic gametophyte, the highest value (0.47) occurred at 12.0 °C; however, Fv/Fm quickly decreased at higher temperatures. In contrast, Fv/Fm in the microscopic sporophyte were less sensitive to temperature, suggesting adaptation to the broad range of temperature with a high value (0.40) that occurred at 21.1 °C. Continuous 6-h exposures to the 50, 100, and 1000 μmol photons m−2 s−1 revealed greater decline in their effective quantum yields of PSII (ΔF/Fm′) in the sporophyte. As known in the photoprotective response and its PSII repair system in the photosynthesis, the recovery of quantum yield in two life-history stages after subsequent acclimation (darkness and dim-light treatments) was more accelerated in dim-light than those of darkness. The response to continuous desiccation (240-min aerial exposure) in two life-history stages was also different, and the ΔF/Fm′ in the gametophyte returned to initial values after re-immersion in seawater. In contrast, those in the sporophyte dropped to zero after a 5-min aerial exposure and did not return to initial values, suggesting that farming protocols for the conchospore seeding in Nori-net cultivation need to pay careful attention to desiccation to ensure successful production.