Interactive effects of temperature and irradiance including spectral light quality on the photosynthesis of a brown alga Saccharina japonica (Laminariales) from Hokkaido, Japan

Abstract

The interactive effects of temperature and irradiance including spectral light quality on the photosynthesis of a brown alga, Saccharina japonica (var. japonica, Laminariales) from Hokkaido, Japan were examined using a pulse amplitude modulation (PAM)-chlorophyll fluorometer and dissolved oxygen sensors. Assessment of maximum quantum yields (in darkness) and effective quantum yields (at 50 μmol photons m−2 s−1) at nine temperatures (4–36 °C, four increments) during 3-d culture indicated a temperature threshold at 24 °C, with early decline of maximum quantum yields at such temperature, which could probably be due to exhaustion of carbohydrate reserves by respiration in prolonged darkness. Unlike maximum quantum yields that was relatively stable through 4–20 °C, effective quantum yields under 50 μmol photons m−2 s−1 gradually declined at low temperatures, revealing light sensitivity under chilling temperatures. Chronic 6-h exposures under 200 (low) and 1000 (high) μmol photons m−2 s−1 at 4, 16, and 24 °C generated a significant decline in effective quantum yields at 4 °C under both irradiances; however, only treatments under low irradiance fully recovered after a subsequent 12-h dim light treatment. Moreover, post-dim light acclimation effective quantum yields of treatments at 16 and 24 °C under high irradiance returned to initial levels, suggesting accelerated photoinhibition at low temperature. Photosynthesis–irradiance responses at 16 °C under blue (450 nm), green (525 nm), red (660 nm), and white light (metal halide lamp) showed that the maximum photosynthetic output occurred under blue and white lights. The photoinhibitory sensitivity to chilling-light stress and the enhanced photosynthesis under blue light of S. japonica presented additional evidence of their physiological adaptation to cold-temperate subtidal waters.