Taxonomic identity and the effect of temperature and irradiance on the photosynthesis of an indoor tank-cultured red alga Agardhiella subulata from Japan

We determined through morphological and rbcL phylogenetic analyses that a previously unidentified, but introduced species of macroalga, which has been easily cultivated in indoor tanks in Japan, is Agardhiella subulata (Solieriaceae). Additionally, the photosynthetic biology of this alga was examined by inducing photosynthetic activity under a variety of water temperatures and photosynthetic active radiation (PAR) to clarify the optimal conditions needed for its efficient cultivation. Photosynthetic activity was evaluated by using both dissolved oxygen (DO) and pulse amplitude modulated-chlorophyll fluorometric (PAM) techniques, and focused on elucidating temperature and PAR levels that would potentially maximize productivity. The DO method revealed that the net photosynthetic rates at 24 A degrees C quickly increased as PAR increased, and approached a P (max) of 27.8 mg O-2 g (ww) (-1) min(-1) (95 % Bayesian credible interval, BCI 23.8-32.1). The maximum gross photosynthetic rate occurred at 26.7 A degrees C (BCI 24.4-28.3 A degrees C). However, PAM experiments indicated that for the maximum quantum yield, the optimal temperature was 23.7 A degrees C (BCI 22.7-24.6) and the maximum relative electron rates occurred when the water temperature was 31.0 A degrees C (BCI 30.6-31.5). This study suggests that the broad tolerance of maximal photosynthetic activity to temperature (22.7-31.5 A degrees C) is one of the main reasons why this alga can be successfully cultivated year-round.