Urban stress and plant adaptation: exploring the morphological, genetic and physiological changes in Populus alba

Cities are the greatest visible sign of human impact on the Earth’s ecosystem. Due to their dense population, transport networks, energy use and increased impermeable surface cover, they radically affect the carbon cycle, as well as the state of the atmosphere and climate. While comprising merely 3% of the Earth’s surface area, urban areas are accountable for a substantial 70% of global CO2 emissions. CO2 is the most worrying greenhouse gas (GHG) due to its rapid increase in concentration in the atmosphere (from the 280 ppm about 150 years ago to the current 420 ppm). Cities are also characterised by other stress conditions such as higher temperatures, increased surface water and rainwater runoff and pollution. The environmental parameter variation mentioned above ensures that urbanisation has a great impact on the environment, ecosystem processes and the ecology of all organisms. Despite numerous studies on the subject, we still know little about how urbanisation affects the organisms‘ evolution in general and plants in particular. Plant life is highly dependent on the environmental conditions in which they grow, so any prolonged stress generates an adap tive and subsequently evolutionary response on their part. In this context, our research aims to exploit plant adaption in urban areas where CO2 concentration has been reported to be higher than the extra-urban area. To evaluate the evolutionary rates of plants in Florence city, where high CO2 levels could accelerate the effects of positive selection on key adaptive strategies, we carried-out biochemical, microscopy and genetic analyses on Populus alba grown in urban and non-urban areas. Through more physiological approaches, we wish to determine how higher CO2 concentrations influence the photosynthetic processes. As the activity of the RuBisCO enzyme is sensitive to changes in CO2 concentrations, rubisco‘s activity is measured by a high-throughput enzyme essay applied to our model species sampledinside andoutsidethecity. Moreover, tocomparechloroplastgenomes,giventheirkeyrolein photosynthesis, we use molecular and genetic tecniques to analyse genome size, structure, gene content and sequence mutations at protein level. Using confocal microscopy, we determine how urban enviroment models the morphological structure of photosyntetic tissues and leaf cuticle. In the end, to assess the impact of the urban environment and the adaptation strategies adopted at the cellular level we use Trasmission Electron Microscopy. The proposed approach will deepen our understanding of the physiological responses of plants to urban climatic and environmental conditions. Furthermore, this research will introduce innovative methodologies for assessing the health of urban vegetation and implementing effective conservation strategies.