Dependency of a Photosynthesis Rate in Nerium oleander L. on Environmental Factors, Leaf Temperature, Transpiration, and Their Change During Vegetation in Subtropics

Abstract

Dependence of net photosynthesis rate in Nerium oleander L. on environmental factors, leaf temperature, transpiration, and also on the changes of these factors during vegetation has been studied under conditions of the Southern Coast of Crimea. The mapping of a photosynthesis response function onto environmental factors in a three-dimensional coordinate system represents a convex surface with the maximum at the top point. This fact makes it possible to obtain numerical coefficients for nonlinear regression equations (simulators) describing interrelations between the net photosynthesis and the main environmental factors, leaf temperature, and transpiration. The data obtained provide a possibility to interpret a photosynthesis rate as a potential ecophysiological characteristic of this species that makes it possible to compare different plant species growing under similar conditions using parameters measured by the same method. Nerium oleander L. has a high photosynthetic potential for acclimatization to high temperatures. If air temperature exceeds the optimum value, photosynthetic intensity sharply decreases. The threshold temperature for leaves is 36.5°С. After the termination of the active growth phase, the maximum net photosynthesis rate decreased during August–October by 51.73%, while transpiration intensity and leaf temperature decreased by 78 and 28.58%, respectively. Compared to August, the optimums of the air temperature, air humidity deficit, and PAR illumination in October shifted to lower values by 17, 89.14, and 31.58%, respectively.