Features of photosynthesis and water regime of <i>Quércus pubéscens</i> Willd. in the conditions of autumn dry of the Southern Coast of the Crimea

Abstract

For Quércus pubéscens Willd. the zones of optimum and threshold values of soil moisture, temperature, illumination, limiting photosynthesis and transpiration, were determined. The dependences of the rate of net photosynthesis (P n ) and the intensity of transpiration (E) on stomatal conductance (g s ), leaf temperature (T l ) and soil moisture (W s ) are shown. The relationship between the speed of the xylem flow in the plant shoot (Sf, Rel. units), the change in the diameter of this shoot (d, mm) and soil moisture has been determined. The relationships between the processes of photosynthesis and respiration under the influence of soil drought made it possible to determine their optimal values: Ws = 26 - 28%, P n = 16 - 18 µmol/m 2 s, P t = 2 - 4 μmol/m 2 s. Changes in the ratio between the components of total respiration (P t , R d , R ph ) under the influence of soil drought were studied. The relationship between the rate of net photosynthesis, total respiration and leaf temperature made it possible to determine the temperature maximum of net photosynthesis (thermal compensation point): P n = P t = 2.0 μmol/m 2 s, at T = 37 ° C. It was found that in the absence of soil drought, the share of respiratory expenditure (R t /P g ) from true photosynthesis is 20 - 23%, and at soil moisture of 8-10% it increases to 55-58%. The obtained research results made it possible to determine the optimal and limiting conditions for the growth of this species and the possibility of its introduction to other regions.