Interactions between temperature and light intensity on growth and photosynthesis of the cyanobacterium Oscillatoria agardhii

Abstract

Oscillatoria agardhii was grown in turbidostat cultures under a 16/8 h light/dark cycle at various combinations of light intensity and temperature. Temperature was found to influence only the maximal growth rate; this relationship was linear over the temperature range studied. An equation was derived describing the growth rate (.mu.) as a continuous function of light intensity and temperature. The light harvesting pigments chlorophyll a and C-phycocyanin increased in concentration when growth became light limited. The regulation patterns observed did not suggest any influence of temperature on their steady state concentrations. The initial slope of the P versus I curves (.alpha.) increased at lower culture irradiances. Values of .alpha. depended on pigment concentration without any influence of temperature. Therefore, .alpha. reflected only the efficiency of the light harvesting process in O. agardhii. From increasing values of .alpha. per chlorophyll a and an increasing C-phycocyanin: chlorophyll a ratio at lower culture irradiances, it was concluded that O. agardhii adapted to lower light intensities by increasing at least the size of its photosynthetic units (PSUs). The maximal photosynthetic activity (Pmax) was influenced by temperature. This was attributed to the influence of temperature on the rate of photosynthetic electron transfer. No indication was found that temperature on the rate of photosynthetic electron transfer. No indication was found that temperature invoked changes in the structure and organization of PSUs in such a way that it affected the functioning of the photosynthetic apparatus. From the pattrens of adaptation to changes in light intensity and temperature it was concluded that they may provide the basis for the survival of Oscillatoria populations during winter seasons, yielding a favourable position of Oscillatoria at the start of the growing season.