Specific features of the water regime of the genus Chaenomeles introduced plants in the steppe zone conditions

Sufficient water supply for plants is one of the most important conditions for their vital activity, since most of the biochemical reactions that regulate the plants physiological functions take place in the water environment. The plants adaptive capacity to the influence of a complex of environmental factors in field conditions is largely determined by the ability to maintain water balance, which can be characterized by various features. Among them, the transpiration intensity and the level of water deficit are the most important indicators that are related to the mechanisms of plant resistance to water or high-temperature stress. The aim of the work was to evaluate the introduction success of plants according to the markers of water availability in a new environment. The objects of the study were plants of the genus Chaenomeles, introduced in the Botanical Garden of Oles Honchar Dnipro National University: three natural species (Ch. japonica, Ch. speciosa, and Ch. cathayensis), as well as two hybrids (Ch. × superba and Ch. × californica). Species Ch. japonica naturally grows in humid areas with moderate temperatures, while species of Chinese origin Ch. speciosa and Ch. cathayensis are adapted to mountainous terrain with sharp temperature fluctuations. Water deficiency in the leaves of introduced plants was determined by saturating leaf cuttings with water; the intensity of transpiration was studied by the method of rapid weighing. Both indicators of the water regime in the leaves of introduced plants were measured under contrasting levels of moisture supply during the growing season in the steppe zone conditions: in the wet period, the dry period, and the period of moisture restoration. It was found that during the drought, the intensity of transpiration increased significantly (P ˂ 0.05) compared to the wet period in the leaves of all introduced Chaenomeles plants, the most (by 1.6–1.7 times) in Ch. japonica, Ch. speciosa and Ch. × superba, the least (by 1.3 times) in the leaves of Ch. × californica. Water deficit in the dry growing season in the leaves of all studied Chaenomeles plants increased significantly (P ˂ 0.05), the most in the leaves of Ch. catayensis (2.8 times compared to the wet period), the least in the leaves of Ch. spesiosa (in 2.0 times compared to the wet period). The level of water deficit in the leaves of both Chinese species was lower than that of Ch. japonica (18.85%). In the leaves of Ch. japonica, Ch. speciosa and Ch. × superba was the fastest recovery of the water balance after drought, as well as the most effective regulation of the transpiration intensity level with the onset of drought and during the recovery period. Introduced plants of the species Ch. japonica, Ch. speciosa and Ch. × superba turned out to be the most adapted to vegetation in the conditions of the steppe climate, which is characterized by periods of drought.