EFFECT OF ENVIRONMENTAL FACTORS ON OPTIMUM TEMPERATURE AND PHOTOSYNTHETIC INTENSITY OF PLANTS ADAPTED TO VARIOUS CONDITIONS

Effects of short-term light of various intensities, CO_2 and temperature changes on the reaction of photosynthetic apparatus of cucumber plants grown for a long time at various levels of irradiation and temperature were studied. A shift of photosynthetic optimum temperature towards higher temperatures was observed with increase in light intensity. Temperature control is more efficient within a range of light intensities, limiting a linear part of photosynthetic light curve. For the plants grown at higher irradiation levels the maintenance of the optimum temperature provided more efficient utilization of the light of low intensities by them. At all the levels of irradiation an increase of growing air temperature of plants by 5℃ led to a shift of the photosynthetic optimum temperature by 1℃ towards higher temperature. The plants grown at 15℃ had a higher photosynthetic rate as compared with those grown at other temperatures. Low rates of CO_2 uptake were observed at a temperature of 30℃. An increase of CO_2 content up to 0.1% at irradiation of 70W/m^2 insignificantly affected the rates of CO_2 uptake as compared with natural concentration. Simultaneous rise of the irradiation level and temperature provided an increase of CO_2 positive effect on photosynthesis. The result indicates that it is necessary to control temperature regime taking into account CO_2 concentration in the air and the preceding light and temperature conditions of plant growth