Authors
Jayvee Ablaña Saco, Satoko Sekida, and Ichiro Mine
February 2018
Abstract
The photosynthesis and growth of the commercially important and edible green seaweed, Monostroma latissimum (Ulvophyceae), from a naturally occurring population in the intertidal area were examined in the laboratory. The natural population inhabits the middle to upper intertidal area and is usually attached to rocks. Cultivation occurs mostly in the shallow and calm waters under full light. The species was subjected to 10, 15, 20, or 25° C temperatures, and irradiances ranging from 0 to 1200 μmol photon m-2 s -1 in order to evaluate the effect of photosynthesis on growth. Photosynthesis was determined and characterized using photosynthesis-irradiance curves from oxygen production and PAM fluorometry. The maximum net photosynthetic rate (per thallus area and total chlorophyll content) did not differ significantly at the different temperatures, which were chosen to reflect the autumn to mid-spring temperatures that the seaweed would be expected to experience. The growth rates over 5 and 10 days were the same for all temperatures, but it decreased at 25° C after 15 days of culturing, which suggested that prolonged exposure to higher temperatures might have an adverse effect on growth. Similarly, the maximum quantum yield decreased as the temperature increased, which indicated that photosystem II (PSII) was under physiological stress at higher temperatures. In contrast, the light compensation point, saturating irradiance, initial slope, and PSII light absorption efficiency increased as the temperature rose. This suggested that the species optimized photosynthesis to accommodate the low and high light conditions that it may experience through its growing season. These conditions are characterized by irradiance limitation and low temperatures in winter, and higher irradiance and temperatures in spring. There were no photoinhibitory responses, which suggested that this alga was tolerant to higher irradiance. The growth rate significantly increased as irradiance rose, which may indicate higher growth rate responses at higher irradiances. Overall, the photosynthetic responses were in parallel with the growth rate response by M.latissimum. Therefore, the results from this study on M.latissimum, photosynthetic characteristics can be used to improve its cultivation.
89-99_12-1