DYNAMICS OF PHYSIOLOGICAL INDICATORS OF TANGERINE IN THE HUMID SUBTROPICS OF RUSSIA

The paper assessed functional state of tangerine plants and the influence of regulatory agrochemicals on this process according to the following indicators: water deficiency and changes in the thickness of leaf blade, changes of the main photosynthetic pigment in leaves (Ca), relative fluorescence quenching index or viability index (Fm/F_T) and photosynthetic activity index calculated by the extrapolation algorithm (Kf_T). It is noted that the graph of water deficiency dynamics shows a clear dependence on the plants’ water availability. It is shown that the onset of water deficiency and recovery from stress does not develop immediately due to the anatomical and morphological features of tangerine leaves (the presence of a cuticle layer and leaf blade’s curling in drought). The introduction of agrochemicals of regulatory and stress-protective action changes the strength of water stress manifestation in different ways, which affects the amount of water deficiency in leaves. A long period of drought and water deficiency developing in tangerine leaves leads to a decrease in the thickness of the leaf apparatus by 1.2–1.4 times. The curve of the photosynthetic activity index (Kf_T) practically does not change during the growing season and completely repeats the change of chlorophyll content in leaves, while the viability index (Fm/F_T) is quite variable (on average V = 25 %) and closely correlates with hydrothermal factors. The viability of plants (Rfd = Fm /F_T) can be regulated by non-root treatments with agrochemicals of growth-stimulating and stress-protective action. The experimental data obtained in the work contribute to the development of effective ways for regulating the functional state of plants and obtaining high-quality fruits under stress.