Temperature characteristics on the growth and photosynthesis of a red alga Phycocalidia tanegashimensis (= Pyropia tanegashimensis, Bangiales) reveal adaptation to subtropical environments due to year-round occurrence of the macroscopic gametophyte

Abstract

The effects of temperature on the photosynthesis and growth of a subtropical red alga, Phycocalidia tanegashimensis (= Pyropia tanegashimensis, Bangiaceae, Bangiales) from Tanegashima Island, Japan, were determined to better understand the ecology of the macroscopic gametophyte. Net photosynthesis–irradiance (P–E) curves, determined at 12, 20, and 28°C, revealed that the maximum net photosynthetic rates occurred at 28°C. A gross photosynthesis–temperature (P–T) curve, determined at temperatures between 8 and 36°C, supported this result and indicated that optimal temperature (\n $$ {T}_{opt}^{GP} $$\n ) for maximum gross photosynthetic rates was 27.3°C (25.9–28.8 95% highest density credible intervals, HDCI). However, after 4 days of incubation at constant temperature, the effective quantum yields (ΔF/Fm ) of photosystem II, determined between 4 and 40°C under 50 μmol photons m−2 s−1 (12L:12D), were greatest at 22.1°C (20.9–23.4 HDCI) and declined quickly below 20°C and 32°C. The relative growth rate (RGR) was highest at 25.8°C (22.5–28.1 HDCI) at the conclusion of a 6-day culture (4 to 36°C) under 50 μmol photons m−2 s−1 (12L:12D). Compared to other temperate species of Bangiaceae, P. tanegashimensis appears to be well adapted to relatively high temperatures. The macroscopic gametophyte stage of Bangiaceae is regarded to be adapted to cold temperatures to overwinter; nevertheless, the significance of our study is that a year-round occurrence of P. tanegashimensis is enabled by its high optimal temperatures for photosynthesis and growth.