The increasing frequency of weather anomalies over the past few years, indicating the rising rate of global climate change, has a negative impact on vegetation communities, particularly in urbanized areas. Thus, plant communities of St. Petersburg experienced physiological stress under the weather anomalies of 2021, 2022 and 2023, which had a depressing effect on their ecosystem functions, such as photosynthetic activity, carbon dioxide assimilation and barrier functions with regard to a number of pollutants, especially such toxic as heavy metals. The work was devoted to the study of the plant communities physiological state both in green spaces along city streets and on the inner-city protected area under the stress caused by combined effect of anthropogenic factor and temperatures increased relative to the norm at different pheno-phases, and showed plants oppression under the described conditions, which expressed in specific and non-specific reactions, such as disturbed barrier functions with regard to pollutants, transition to respiration in a daytime with carbon dioxide emission, which leads to an increased risk of territories and their ecosystems due to pollutant concentrations potential reaching values corresponding to phytotoxicity and accumulation of CO2 in elevated amounts in residential areas.