Morphological and physiological responses of Porphyra suborbiculata Kjellman (Bangiales, Rhodophyta) blades from five localities

Abstract

Archeospore germlings of five strains of Porphyra suborbiculata from tropical to sub-tropical (Ilocos Norte, Philippines and Shangwei, China, respectively) and warm-temperate waters (Kagoshima and Enoshima, Japan and Tongyoung, South Korea) were cultured under two photoperiod regimes (14L:10D and 10L:14D) and different temperature conditions (5, 10, 15, 20, 25, and 30°C) at 60–80 umol m^-2 s^-1 photon flux density in the laboratory. The blades of the Philippines and China strains grew at 15–30°C with optimum growth at 20–25°C under both photoperiods, while the strains from Japan and Korea tolerated a temperature range of 10–25°C under both photoperiods and grew best at 10–20°C under SD conditions. The specimens from the Philippines and China had varying blade shapes in culture while the Japanese and Korean strains had prominent round to ovoid blades and linear to lanceolate blades under long and short day-length conditions, respectively. Archeospore liberation was observed earlier in higher temperatures for all strains, regardless of photoperiod. Sexual reproduction occurred within the optimum growth conditions (20–25°C for the samples from the Philippines and China, and 10–20°C for the warm temperate samples) of all strains under both photoperiods. The Philippines specimens had blade spores that developed directly into ‘‘spoke-like conchosporangia’’ restrictively at 30°C, without observed fertilization. The appearance of 2–3-celled marginal denticulation generally occurred earlier at higher temperature under longday conditions. The Chinese strain had a smooth-edged shape, denticulate cell margin and contrasting cell number (4–5 cells) at 25°C. Porphyra suborbiculata exhibits wide geographic distribution, and the temperature and photoperiod tolerance shown here could imply adaptation and differentiation within a species to varying environmental conditions.