Actions and Interactions of Temperature, Light Intensity and Nutrient Concentration on the Growth of the Green Alga, Chlamydomonas reinhardi Dangeard

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Abstract
The unicellular green alga, Chlamydomonas reinhardi, was cultured at several temperatures in Chu's No. 10 medium under 150 foot-candles illumination. Specific growth rates based on cell counts were found to fit a typical activity curve. The range of temperature tolerance was 6 °C to 35 °C and the optimum was 28°.The culture series was repeated at light intensities of 75, 110 and 200 f-c in turn. These changes in illumination did not alter the limits of temperature tolerance or the optimum, though the reduced intensities caused decreases in growth rates. At the reduced intensities light acted as the typical limiting factor. At 200 f-c the growth temperature relation was the same as that for 150 f-c, indicating that some factor other than light intensity had become limiting at the latter levels.The series was then repeated with the light intensity held at 200 f-c but with the total concentration of nutrient salts doubled. This accelerated growth between 12° and 30°, showing that some nutrient salt was indeed the limiting factor in the experiments with 200 f-c. However, the increase in salt concentration also shifted the lower limit of temperature tolerance up to 12° and moved the optimum down to 18°. Hence the salt concentration must have played some role besides that of limiting factor.Finally, the results of this investigation are discussed from the standpoint of the system of environmental factors described by Fry (1947) and some of the ecological implications of the observations are considered.