Features of Temperature Adaptation of Phaeodactylum tricornutum, Nitzschia sp., and Skeletonema costatum (Bacillariophyceae) under Different Light Conditions.

Two types of possible adaptive response of the photosynthetic apparatus of diatoms to the changes in growth temperature conditions are shown. The first type is a temperature-dependent change in the content of chlorophyll in the cell, aimed at matching the rates of light and dark reactions of photosynthesis (noted in Phaeodactylum tricornutum and Nitzschia sp. 3). At the limiting light intensity, a temperature decrease from 20 to 5°C leads to an increase in the initial slope of light dependence of the C/Chl ratio; under the optimal light conditions at a temperature decrease from 20 to 10°C and from 10 to 5°C, the C/Chl ratio increases 1.5-fold in both species. The second type of response to the changes in growth temperature conditions was observed in Skeletonema costatum, for which the chlorophyll content in the cell does not depend on the temperature in the range of 10-20°C. The adaptation of the photosynthetic apparatus in this case probably occurs due to the changes in the activity of enzyme systems and in the rate of enzyme processes. The potential productivity of all studied species of algae at 10°C, calculated as the increase in biomass per unit of chlorophyll per day, does not differ significantly. Under the conditions of light inhibition, a temperature decrease leads to a progressive decrease in the content of chlorophyll in the cells of all algal species under study due to a decrease in the rate of pigment synthesis against the background of its intense photooxidation.