Dependence of Stomatal Conductance of Siberian Fir Needles on Illumination

A dependence of Siberian fir (Abies sibirica Ledeb.) needle transpiration on the intensity of photosynthetically active radiation (PAR) was studied. Stomatal conductance was estimated indirectly by analyzing the intensities of diffusion of water vapor and CO2 under conditions of controlled PAR. The study was performed using the LI-COR LI-6400XT infrared gas analyzer and opaque chamber for conifers on intact Siberian fir shoots in the middle taiga subzone of the North–East of the European part of Russia. It was demonstrated that in the absence of soil moisture deficiency, constant leaf temperature, and water vapor concentration in the atmosphere, a change in the transpiration intensity is determined by the size of the stomatal pore. An association between stomatal conductance and PAR intensity was established: at PAR intensity equal to zero, the stomatal conductance is minimal, but not zero; with an increase in the PAR intensity to 15 μmol quanta m–2 s–1, the conductance increases to maximal, corresponding to the environmental conditions and remains constant with any changes in the PAR intensity; with a decrease in the PAR intensity to 25 μmol quanta m–2 s–1, the conductance decreases to a level corresponding to zero PAR intensity and given external conditions. Thus, at a constancy of other environmental factors, the stomatal conductance is managed by the PAR intensity; however, the management is not regulatory in nature (at which a certain conductance value corresponds to a given intensity), but is a factor triggering the opening and closing of stomata.