The effect of moisture deficiency on the photosynthesis of evergreen shrubs of the genus <i>Cotoneaster</i> L
The paper presents data on the features of the water regime (water deficit, water-retaining forces, and total hydration of leaf tissues) in four evergreen species of the genus Cotoneaster , as well as the effect of the growing water stress on the course of primary photosynthesis processes. It was found that during the periods of maximum impact of dry factors of the summer season on the Southern Coast of the Crimea, the species Cotoneaster salicifolius and Cotoneaster graucophyllus var. serotinus show signs of increased drought resistance, which is manifested in the ability to economically consume moisture by leaf tissues during wilting, and subsequently restore the normal turgescence of leaf tissues. These species maintained minimal levels of water deficit in the leaves, and the sublethal level was 12% water loss. The genotypes Cotoneaster × watereri 'Cornubia' and Cotoneaster franchetii showed relatively weak water retention capacity combined with low leaf repair capability. Water loss of more than 8-10% was already critical, after which the number of intact leaf blade tissues was unsatisfactory (less than 60%). It was found that the parameters of chlorophyll fluorescence induction (CPI) are most sensitive to lack of moisture and they are features of fast phase. Water deficiency within 10% leads to irreversible disturbances in the photosynthetic apparatus in Cotoneaster franchetii , which was expressed in a decrease in the ratio of variable and base fluorescence below the norm of vitality and the absence of pronounced peaks on the CPI curve. In the species Cotoneaster salicifolius and Cotoneaster graucophyllus var. serotinus , an increase in the level of water deficiency was accompanied by a decrease in the efficiency of the light phase of photosynthesis and an increase in the number of unrecoverable Q<sub>a</sub><sub />in the reaction centers of PS2. However, these changes were reversible. It is concluded that the species Cotoneaster salicifolius and Cotoneaster graucophyllus var. serotinus are relatively resistant to lack of moisture and are characterized by a high level of water-retaining forces and stable operation of the photosynthetic apparatus. Controlled wilting in combination with the CPI method can be used for quick diagnostics of the drought resistance of Cotoneaster species.