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

EFFECT OF VARIOUS TEMPERATURES IN THE ROOT ZONE AND LIGHT INTENSITIES ON PHOTOSYNTHESIS AND TRANSPIRATION OF TOMATO PLANTS

Photosynthetic intensity, transpiration and stomatal resistance (R_s) of tomato plant leaves were studied at various light intensities and temperatures in the root zone. Temperature regime had an insignificant effect on a gas exchange of plants at an irradiation of 900μmol m^<-2> s^<-1>. Less irradiation, 180μmol m^<-2> s^<-1>, resulted in a relatively greater effect of temperature on CO_2 uptake. Transpiration rate and stomatal resistance to CO_2 varied slightly within a wide range of temperature changes. An increase and decrease of R_s were observed only at low (<14) and high (>28℃) temperatures, respectively. Reverse dependence was found for the process of transpiration. The highest transpiration coefficient Ph/T was observed at 20℃. The results indicate that it is necessary to take all the aspects of plant activity into account for determining optimal growth conditions