The frequency of extreme heat effects has recently increased in European cities due to climate change. The problem appears to be critical in urban areas where manmade structures significantly alter the temperature balance, thus highlighting the importance of sustainable management and proper inventory of urban green zones. Based on this, the paper provides a case study on using a combination of open-access and low-cost urban greenery inventory methods that could be used by municipal governments and private land managers to estimate the contribution of urban trees to the mitigation of urban heat impacts. The research focuses on the urban greenery inventory of courtyards in high-rise residential districts of the city of Kyiv (Ukraine), aiming to estimate the adapting potential of urban vegetation against heatwaves. Visual and thermal satellite images of Kyiv enabled us to estimate how the density of buildings and greenery is distributed and analyze the surface temperature in residential districts. A UAV thermal imaging survey was made in four selected locations with varying vegetation coverage, followed by leaf-based field instrumental analysis of photosynthetic activity in selected city tree species at hot temperatures. In addition, 16 portable temperature and humidity sensors were installed in shaded and sunlight-exposed areas of the locations in focus to assess the microclimate formation impact of trees in a high-rise residential courtyard. The Ukrainian legislation on the management of green spaces in cities was reviewed to find out whether it promotes the shaping of comfortable microclimates in residential districts; follow-up recommendations were made on how to improve the applicable provisions.

Climate change and nutrient pollution are echoed by worldwide increasing trends in the frequency, duration, and toxicity of cyanobacterial (blue-green algal) blooms. Therefore, searching for the best options to mitigate blooms is relevant and timely. Aquatic vascular plants offer a promising solution through biological control. In this study, we use reservoirs regularly affected by intensive blooms (the Kyiv and Kaniv Reservoirs of the Dnipro River, Ukraine) to investigate whether macrophytes may inhibit or reduce the massive development of cyanobacteria. Special attention was paid to plants with floating leaves and free-floating plants since data on their effects on cyanobacteria are controversial. On the basis of field and satellite observations, the spatial distribution of cyanobacterial blooms and aquatic macrophyte patches was assessed. Multispectral images captured by satellites Sentinel-2a (S2A) and Sentinel-2b (S2B) were used. In addition, based on data from field observations, a comparative analysis of phytoplankton and physical and chemical parameters between areas of the reservoirs overgrown and not overgrown by macrophytes was carried out. The obtained results indicate that in macrophyte patches phytoplankton structure differed from that observed in open waters. However, in areas of reservoirs dominated by floating-leaf plants or free-floating plants, a significant decrease in phytoplanktic or cyanobacterial biomass was not observed. This is most likely due to the fact that these macrophytes did not reduce the concentration of biogenic substances to a level that would limit cyanobacterial growth. On the contrary, intensive overgrowth of floating-leaf plants (in particular, Trapa natans) along the river sections of the reservoirs, as well as other factors, contributed to nitrogen and phosphorus enrichment. Therefore, in the face of relevant nutrient supply, these ecological groups of macrophytes (floating-leaf plants and free-floating plants) have not shown statistically significant effectiveness in controlling the process of cyanobacterial blooms in reservoir ecosystems.

Chlororespiration is the uptake of oxygen into the respiratory electron transport chain (ETC) localized in the thylakoid membranes of chloroplasts. The chlororespiratory ETC interacts with photosynthetic electron transport and participates in the non-photochemical reduction/oxidation of the plastoquinone pool (PQP) accompanied by O₂ consumption. The two key thylakoid enzymes in chlororespiration are the plastid-encoded NAD(P)H dehydrogenase complex (NDH) and the nucleus-encoded terminal plastoquinol oxidase (PTOX). The contribution of chlororespiratory electron flux to the total electron flow in non-stressed plants is considered insignificant. In contrast, under abiotic stresses, chlororespiration appears to be triggered, at least in some photosynthetic organisms, acting as a protective alternative electron transport pathway. There is evidence of NDH complex and PTOX increasing their activity and/or abundance when plants experience high light, drought, heat, or low-temperature stresses. Alternative electron transfer to oxygen via PTOX protects PQP from over-reduction under stress conditions. For instance, it was shown that PTOX-dependent electron drainage accounted for up to 30% of total PSII electron flow in salt-stressed plants. PTOX is not bound to the thylakoid membrane in dark-adapted leaves but is associated with it at intense illumination and high transmembrane proton gradient (ΔpH) or membrane potential (Δψ). It was also shown that PTOX is capable of lateral translocation from stromal lamellae to granal thylakoid stacks under salt stress. Such changes in PTOX localization increase the accessibility of the substrate (plastoquinol) and the turnover rate of the enzyme. The available data allow considering PTOX as a possible target for manipulation to increase stress tolerance in sensitive plants.

Throughout the world, river basins are directly or indirectly affected by human activities, reducing local and global biodiversity and preventing the ecosystem from properly functioning. Our research focused on the Irpin River basin (Ukraine), whose water bodies have experienced various impacts due to human activities, including the unexpected extremes caused by military operations in the catchment area: long-term flooding, disturbance of free flow, significant water level fluctuations, etc. The study hypothesized that the primary factors determining the structural and spatial distribution of quantitative indicators of microalgae and aquatic macrophytes are the result of various hydromorphological changes, that lead to changes in the physical and chemical parameters of the aquatic environment. Very high values of chlorophyll a in the water column (59–106 µg · L⁻¹), an increase in the abundance (number of cells) and biomass of algae (due to the predominance of certain groups in the transformed sections), as well as saprobic index were recorded in the sections of the Irpin River basin that underwent significant hydromorphological changes. Our results revealed a strong correlation between phytoplanktonic (in the water column) chlorophyll a levels and water temperature (r = 0.76, p < 0.001), as well as organic phosphorus and polyphosphate concentrations (r = 0.61, p < 0.01). ANOVA and Monte Carlo permutation tests in a Canonical Correspondence Analysis (CCA) showed that the abundance of different divisions of phytoplankton and phytobenthos were significantly and similarly related to several environmental variables. We observed a positive correlation between the number of cyanobacteria and the concentration of ammonium nitrogen, nitrites, and phosphorus compounds. An increase in dissolved organic matter in the water can explain the increase in the biomass of Dinoflagellata and Euglenophyta. Species richness and the cover values of the macrophytes also clearly reflected changes in vegetation activity in sections of the Irpin River caused by hydromorphological changes. The results indicated that long-term flooding had the most negative impact on macrophyte communities. At some sites, the impact was so severe that the number of macrophyte species was very low. The total number of macrophyte species showed a significant negative correlation with total suspended solids (r = −0.51, p < 0.05) and phytoplankton chlorophyll a concentration (r = −0.73, p < 0.001). Our results provide a scientific basis for predicting changes in riverine microalgal and aquatic macrophyte communities due to extreme hydrological events.