The effect of irradiance and temperature on the photosynthesis of Hydropuntia edulis and Hydropuntia eucheumatoides (Gracilariaceae, Rhodophyta) from Vietnam

Abstract

:The effect of irradiance and temperature on the photosynthesis of two Vietnamese edible algae, Hydropuntia edulis and H. eucheumatoides (Gracilariaceae, Rhodophyta), were determined using dissolved oxygen sensors and pulse amplitude–modulated fluorometry. Modeling the net photosynthesis–irradiance (P-E) responses of these species at 26°C revealed that the net photosynthetic rates quickly increased at irradiances below the estimated saturation irradiance (Ek) of 137 and 74 μmol photons m−2 s−1, with a compensation irradiance (Ec) of 40 and 29 μmol photons m−2 s−1, respectively. Gross photosynthesis and dark respiration rates determined over a range of temperatures (14°C −42°C) revealed that the highest gross photosynthetic rates were 7.1 and 4.7 mg O2 gww−1 min−1 and occurred at 31.2°C and 30.5°C, respectively [95% Bayesian credible interval (BCI): 30.4–31.8 and 29.0–31.8]. The dark respiration rates for both species initially increased linearly and began to decline above 34°C. The measured dark respiration rates ranged from 0 to 2.3 mg O2 gww−1 min−1. The values of maximum effective quantum yield (ΦPSII at 0 μmol photons m−2 s−1) occurred at 22.4°C (BCI: 21.2–23.3) and was 0.48 for H. edulis and at 22.8°C (BCI: 22.1–23.3) and was 0.49 for H. eucheumatoides. The temperature response of these species indicated that they were well adapted to the annual range of seawater temperatures in the study site but were likely close to the marginal temperatures for the optimum photosynthesis.