SEASONAL VARIATION OF GROWTH RATE OF VARIOUS STRAINS OF UNICELLULAR ALGAE UNDER NATURAL LIGHT- AND TEMPERATURE-CONDITIONS

Abstract

(1) Using a simple method of test cultures, seasonal variation of growth rate of various strains of unicellular algae under natural light- and temperature -conditions was investigated.
(2) The strains of ordinary temperature tolerance ("mesophilic"), such as Chlorella ellipsoidea, showed positive growth in all months throughout the year, although their growth was considerably suppressed in the hottest month, August. In contrast, the thermophilic strains grew actively in summer months, but showed no growth in winter months, December, January and February.
(3) Taking into consideration the quantity of solar radiation and the energy content of algal cells, the efficiency of solar energy conversion shown by some algal strains was calculated. In the case of Chlorella ellipsoidea the efficiency (on a total radiation basis) was highest in October and November (5.3 percent) and lowest in January and August (1.3-1.4 percent).
(4) It was shown that the growth rate of algae determined by the test cultures agreed fairly well with the actual yield obtained from the open outdoor cultures in each season. It was inferred that from large-scale outdoor cultures using mesophilic and thermophilic strains adequately according to the season, a yield of 18 metric tons (dry weight) of algae may be obtained per acre per year.