Dynamics of the Rate of Photosynthesis in Juniperus excelsa M. Bieb and Environmental Factors during Growing Seasons in the Conditions of the Southern Coast of Crimea

Abstract

Abstract—The objectives of the work are to study the relationship between the rate of photosynthesis and transpiration, as well as temperature, in Juniperus excelsa M. Bieb and the main external environmental factors and determine the optimal and limiting growth conditions for this species in the conditions of the Southern Coast of Crimea (May–September). Similar studies have not yet been carried out in these conditions; therefore, this will allow the results to be extrapolated for introduction of the species to other regions. Finding the function of photosynthesis response to environmental factors in Juniperus excelsa M. Bieb allowed for estimating the numerical coefficients of nonlinear regression equations of these parameters. Juniperus excelsa Bieb M. has a high photosynthesis potential to acclimate to elevated temperatures. An increase in needle-leaf temperature above the optimum resulted in a dramatic reduction in the rate of photosynthesis; the critical temperature is 38°C. During the studied period of plant vegetation, external environmental factors and ecological–physiological characteristics of the species varied: rate of net photosynthesis decreased by 28.58%, while transpiration and needle-leaves temperature dropped by 50 and 6.67%, respectively. The temperature and light optimums similarly decreased, that is, temperature and humidity deficit by 10.72 and 60%, respectively, and illumination by 15.4%. The findings will serve to compare the obtained ecological–physiological characteristics with climate conditions in a specific region and assess the possibilities of introducing Juniperus excelsa M. Bieb into other regions.