The flora of the steppe Dnieper region is characterized by an abundance of naturalized alien species, some of which colonised over the last decade. Climate change, associated primarily with increasing temperature, became clearly manifested in this period. We tested the hypothesis that there is an association between climate change and the initiation of invasiveness of some alien plant species in the steppe Dnieper region. For this purpose, comparative studies of the distribution boundaries of naturalized alien trees, shrubs and herbaceous plants were conducted. Along the research route numerous 5-10-year-old broadleaf linden trees (Tilia platyphyllos Scop.) were found in the man-made plantation communities of Dnipro city in areas with moist soil; seeded undergrowth was located at a significant distance from the adult linden plants. Numerous groups of young 7-10-year-old plants of the smoke trees (Cotinus coggygria Scop.), which had a seed origin, were found in the shelterbelt and urban recreational plantations. Young 10-12-year-old virginal and generative plants of the black cherry (Padus serotina Ehrh.) were found in large numbers in both the seminatural and artificial plant communities at great distances from the adult trees. The alien plant species common hackberry (Celtis occidentalis L.) showed the ability to form fairly sparse seminal seedlings, which was presented by the plants at the age of 4-7 years in both the natural and urban plant communities. The perennial herbaceous plant common milkweed (Asclepias syriaca L.) was found in the course of the research in ruderal habitats, urban plant communities, and also in the agrocoenoses. The common milkweed reached its greatest abundance in fields of winter crops, where the spread of this species was accompanied by a sharp decrease in the number of other species of segetal plants. Our study results confirm that the extension of the distribution boundaries of alien species over the last decade was not related to the ground conditions of the steppe Dnieper region. At the same time, changes in climatic conditions were favourable for some naturalized alien species because they have created the opportunity for seed reproduction of species away from the maternal plants. Alien species C. coggigria, P. serotina and A. syriaca were also the most sensitive to the influence of the climate changes. Consequently, these species have the greatest potential for increasing their level of invasiveness and endangering the biodiversity in the steppe Dnieper region under conditions of climate change. We suggest that a simultaneous initiation of invasiveness of these several alien species leads to an increase in the degree of threat to the diversity of natural plants in the region. The study results confirm the urgent need for analysis and forecasting of the consequences of introduction of alien species, in order to prevent the undesirable effects that this would bring for the region's native vegetation.

Climatic change can influence the boundaries of the natural and alien plant species distribution. Fluctuations in air temperature, relative humidity and other factors can become a stimulus to initiation and / or intensification of the invasive nature of some adventive plant species, especially in areas with a high degree of anthropogenic transformation. This paper presents an analysis of the current state and a forecast of the invasiveness of the alien species Ulmus pumila L. (Asiatic elm) in the Northern Steppe Dnieper under conditions of climatic change. Two local U. pumila populations consisting of young different age trees were found during a route survey in the territory of the large industrial city Dnipro (48°28′00″ N, 35°01′05″ E) in its left-bank and right-bank parts.The seed origin of both local populations of Asiatic elm is confirmed by the fact that the young plants were spaced at a distance of 50 to 120 m from adult trees, which could potentially be parent plants. Both the left-bank and right-bank populations of U. pumila were located on abandoned construction sites, where there were numerous reinforced concrete slabs, piles and abundant construction debris. In both U. pumila local populations, 100 different-aged trees were randomly selected throughout the site, and their age and the morphometric parameters were measured to simulate the development process of the detected populations, provided the current trends of climate change continue. Analytical dependence of the number of trees in the left-bank local U. pumila population on development time was described by a polynomial model with a determination coefficient of 98.3%. The graphic representation of this model had a sinusoidal character, and a similar dynamic of left-bank population growth in the subsequent years was suggested. The dynamic of the number of trees in the right-bank local Asiatic elm population was described by an exponential model with a determination coefficient of 84.4%, and its graphical representation was exponential. According to the forecast, by 2020, the number of plants in the right-bank local population of U. pumila can increase 4-fold in comparison with 2015 while maintaining the current dynamic of population development. Thus, the created mathematical models adequately described the dynamics of development of both local populations during the last 15 years and predicted their subsequent intensive growth, confirming the initiation and intensification of the invasive nature of the alien species U. pumila by climatic change in the Steppe Dnieper.

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The influence of transport fumes and industrial waste on the activity of catalase, benzidine-peroxidase and guaiacol-peroxidase was studied in the dormant buds, leaves and seeds of the following species of the genus Tilia:T. platyphyllos Scop., T. europaea L., T. amurensis Rupr. and T. begoniifolia Stev. We tested the hypothesis that the action of pollutants changes the state of antioxidant protection at different stages of tree development in contaminated phytocenoses. An increase in catalase activity was observed in leaves of all linden species, and the action of transport fumes caused excess over control level by 118, 118, 196, and 61% respectively for T. platyphyllos, T. europaea, T. amurensis and T. begoniifolia. The action of industrial waste was accompanied by a slight decrease in catalase activity in T. europaea leaves, and increase in activity in leaves of T. amurensis and T. begoniifolia (143% and 115%). Benzidine-peroxidase activity increased due to the influence of transport fumes on leaves of T. amurensis and T. begoniifolia (103% and 44%), but decreased due to the effect of industrial waste on leaves of T. europaea, T. amurensis and T. begoniifolia (46%, 30%, and 44% respectively), and was suppressed in the seeds of T. europaea, T. amurensis and T. begoniifolia both under the influence of transport (42%, 47% and 33% below control) and industrial emissions (19%, 19% and 45%), and was reduced in buds of T. platyphyllos, T. europaea and T. amurensis due to the effect of transport fumes (21%, 9% and 20% respectively). Guaiacol-peroxidase activity decreased due to the influence of transport fumes in buds of T. platyphyllos, T. europaea and T. amurensis (41%, 14% and 47% below control), while it increased in the seeds of T. platyphyllos and T. amurensis (104% and 83%), as well as in leaves of T. amurensis and T. begoniifolia both due to the effect of transport (129% and 144%) and of industrial emissions (respectively, 34% and 40% above control). The substantial restructuring of the antioxidant system components in leaves, dormant buds and seeds confirms the hypothesis that metabolic processes in Tilia trees adapt throughout all stages of their development in response to the polluted conditions in urban phytocenoses.

The paper presents the results on resistance of Aesculus hippocastanum Linnaeus, 1753 trees to Cameraria ohridella Deschka & Dimić, 1986 (Lepidoptera, Gracillariidae) impact under conditions of a modern urban environment on the example of Dnipro city as the largest industrial city in Ukraine. Field experiments were conducted in all park areas of the city, which allowed covering the full gradient of the existing urban environment and considered the different degrees of the tree settlement by the invasive insect species. The research of the impact of C. ohridella caterpillars’ vital activity on the photosynthetic apparatus state was carried out by applying a chlorophyll fluorescence induction technique. Diagnosis of photosynthetic dysfunction of fresh Ae. hippocastanum leaves was conducted using a portable “Floratest” fluorometer manufactured in Ukraine. Interpretation of the obtained Kautsky curves showed that significant changes in their critical parameters associated with the degree of leaf damage by C. ohridella caterpillars were not detected. The influence of tree growth site conditions on the following 4 main indicators of chlorophyll fluorescence induction was established: the initial value of fluorescence induction after irradiation; the value of “plateau” fluorescence induction; the maximum value of fluorescence induction; the stationary value of fluorescence induction after light adaptation of the plant leaf. It was found that the efficiency coefficients of photochemical processes in Ae. hippocastanum trees growing in low terrain levels differed significantly, which can probably be interpreted as their response to the specific characteristics of the urban environment.

The complex of invasive species of phytophagous insects that can adapt to novel living conditions is constantly increasing. The ecological effect of their vital activity in the new environment is almost impossible to predict. As a result, invasions undesirable in the economic sense are often observed. The horse -chestnut leaf miner (Cameraria ohridella Deschka & Dimič, 1986, Gracillariidae) is one of these problematic invader species in the introduced range of the horse chestnut (Aesculus hippocastanum (Linnaeus, 1753), Sapindaceae). We studied the effect of C. ohridella on the state of the photosynthetic apparatus in Ae. hippocastanum leaves. Photosynthesis is the one of the processes most vulnerable to stress factors, so information about the state of photosynthetic apparatus in a plant under the influence of phytophage feeding obtained with fluorescence analysis can be significant. The feeding effect of C. ohridella caterpillars on the functional state and activity of Ae. hippocastanum photosynthetic apparatus was studied. We studied critical parameters of chlorophyll fluorescence induction reflecting the effect of a single C. ohridella generation (feeding the caterpillar for the five stages of this species’ development) on the functional links of the photosystem II in Ae. hippocastanum leaves. The data obtained show a decrease in PS II quantum efficiency (inhibition of photosynthetic activity) in the leaves from different parts of the crown; it suggests the destructive effect of C. ohridella caterpillar feeding on Ae. hippocastanum photosynthetic apparatus. Values of all key parameters of chlorophyll fluorescence indication evidence inhibition of photophysical and photochemical processes of photosynthesis and impaired coherence of Calvin cycle reactions. Study of the feeding effect of C. ohridella caterpillars on the efficiency of the main enzyme in the Calvin cycle (which closely correlates with the coefficient of fluorescence induction that characterizes the efficiency of dark photosynthetic processes) showed a significant decrease in its activity in the leaves of both the illuminated and shaded parts of the crown. Our study has shown that the method of chlorophyll fluorescence induction allows one to determine the general state of a plant in an express regime by evaluating the main process of plant life as photosynthesis. Analysis of chlorophyll fluorescence parameters is a powerful and effective tool for determining the effect of phytophages on the plant body. The obtained data allow us to apply the method of analyzing chlorophyll fluorescence induction in practice to establish the physiological state of tree flora in forests and garden farms.

We examined the vital condition of the common oak (Quercus robur L.) in plantations of different categories in Dnipro-city. In the investigated plantations, differences in the individual resistance of plants were recorded. The patterns of changes in the pigmented complex of leaves exposed to atmospheric pollution from motor vehicle emissions were studied in connection with the life state of oak trees. The content of chlorophyll a had, in all variants of the experiment, significantly higher values than chlorophyll b. Chlorophyll a accounted for 52.4–75.0% of the total content of chlorophylls, and chlorophyll b (25.0–47.6%). Regardless of the level of air pollution, relatively healthy oak plants were characterized by a high content of pigments activity in the photosynthetic apparatus of the leaves. A chronic moderate influence of motor vehicle emissions had a positive effect on the content of green pigments and carotenoids. Increase in the intensity of transport emissions resulted in a significant reduction in the accumulation of chlorophylls and to an increase in carotenoids. The stability of the chlorophyll a / chlorophyll b ratio under the influence of motor vehicle emissions was been registered. Only severely damaged common oak trees showed a decrease of this parameter by 29.3% compared with healthy and moderately weakened specimens of oak. The values of the coefficients of variation in the content of chlorophylls, their amounts and ratios, as well as carotenoids were low and represent less than 19.0%, while the amplitude of the variability of the studied parameters of the pigment complex, depending on the life state of plants and the intensity of transport emissions, was quite significant: the highest fluctuations in the сontent indexes were recorded for chlorophyll a, the sum of chlorophylls a + b in trees from the park area and the area with a medium level of pollution, chlorophyll b only in oaks from the street with an average level of air pollution by transport emissions. The smallest variability was a characteristic of the ratio of chlorophylls a / b and the content of carotenoids. Low values of the ratio of the sum of chlorophylls a + b to carotenoids (4.3–5.2) indicate the stress state of oak plants in urban environments.

Climatic changes observed around the world in recent years are associated with an increase in the solar radiation intensity and temperature and reduction in the humidity. Fluctuations of environmental factors significantly change the conditions for the existence of plants, which dictates the need for adaptive reactions of plant organisms at the different levels of their organization. Such dangerous processes as excessive heating of the surface of plant leaves and water loss can be prevented by the formation of a cuticle, which is a complex composition consisting of cutin and the soluble intracuticular and epicuticular waxes. We suggested that the structure, component composition and properties of the cuticle of trees undergo adaptive changes due to microclimatic conditions in different parts of the tree crown. The study was aimed at the identification and evaluation of light-induced differences in the accumulation and composition of leaf epicuticular waxes of Ulmus trees (native U. minor Mill. and alien U. pumila L.), and was conducted in 2018–2019 in Dnipro city located in the steppe zone of Ukraine. Analysis of the waxes’ chloroform extracts was carried out using GC Shimadzu 2010 PLUS equipped with a flame ionization detector and capillary column SP-2560. The highest amount of epicuticular waxes (12.23 ± 0.39 µg/cm2) was on the sunlit leaves of U. pumila, and wax deposits on the sunned leaves exceeded twice those on the shaded leaves in both U. minor and U. pumila. Long-chain hydrocarbons detected in the epicuticular waxes of both elm species were represented by free fatty acids, aldehydes, alcohols, and n-alkanes in various ratios. In the epicuticular waxes of U. minor, fatty acids dominated both on shaded and sunned leaves, while alkanes together with alcohols were the main components in U. pumila waxes, especially on the sunlit leaves. According to our results, local high illumination of leaves in the crown of both elm species caused increase in share of long-chain alkanes (1.2–1.9 times), but simultaneous reduction of the content of free fatty acids (1.5–16.8 times) in the epicuticular waxes’ composition. General patterns of the leaf epicuticular waxes’ modification due to increased solar radiation and air temperature can indicate the adaptive metabolic responses of woody plants to changing climatic conditions.