Photosynthetic performance of Saccharina angustata (Laminariales, Phaeophyceae) at the southern boundary of subarctic kelp distribution in Japan

Abstract

ABSTRACTEffects of photosynthetically active radiation (PAR) and temperature on the photosynthesis of a subarctic edible brown alga, Saccharina angustata (Laminariaceae, Laminariales), from Hokkaido, Japan, were determined using a pulse amplitude modulation (PAM)–chlorophyll fluorometer and optical dissolved oxygen sensors. Photosynthesis–PAR experiments at 8, 16, and 20 °C revealed highest net photosynthetic rates at 16 °C; whereas, the temperature effect on maximum quantum yield (Fv/Fm) showed the highest Fv/Fm at 7.0 to 8.4 °C. These temperatures corresponded to the optimum temperatures for growth of Japanese Saccharina species. The maximum gross photosynthetic rate from gross photosynthesis–temperature curve was at 21.2 °C. Though consistent with the highest seawater temperature in the study site, it is close to the limit for thermal inhibition, because Fv/Fm above 20 °C was compromised after 48–72 h of incubation. Continuous 6-h exposures to PAR of 200 µmol (low) and 1000 µmol (high) photons m−2 s−1 at 8, 16, and 20 °C caused chronic photoinhibition in the alga, with greater declines in effective quantum yields of photosystem II (ΦPSII) and failure of recovery in post-dark acclimation Fv/Fm under high PAR. This physiological performance provides a basis for understanding the persistence of S. angustata near its southern boundary in the western Pacific.