Features Of Photosynthesis And Water Regime Of Quercus Pubescens Willd. Under The Conditions Of Autumn Drought Of The Southern Coast Of The Crimea

The Nikitsky Botanical Gardens – National Scientific Center of the RAS, 52 Nikitsky spusk street, Nikita village, Yalta 298648, Russia

^* Corresponding author: ilnitsky.oleg@mail.ru

Abstract

The objective of the research is to determine the optimal zones and thresholds of soil moisture, temperature, illumination, limiting photosynthesis and transpiration of Quércus pubéscens Willd. and allowing the introduction of the species to other regions. The dependences of the net photosynthesis rate (P_n) and the transpiration rate (E) on stomatal conductivity (g_s), leaf temperature (T_l), and soil moisture (W_s) are shown. The ratio of the processes of photosynthesis and respiration, under the influence of soil drought, allowed us to define their optimal values: W_s = 26 – 28%, P_n = 16 –18 μmol/m²c, Rt = 2 – 4 μmol/m²c. The relationship between the net photosynthesis rate, total respiration, and leaf temperature allowed us to determine the temperature maximum of net photosynthesis (the thermal compensation point): P_n = R_t = 2.0 μmol/m²c at T_l = 37ºC. It was found that in the absence of soil drought, the proportion of respiratory costs (R_t/P_g) from true photosynthesis is 20 – 23%, and with soil moisture of 8 – 10% increases to 55 – 58%.