Urban forests, provenance matters: Investigating its influence on growth and physiological responses to drought in Quercus robur and Acer pseudoplatanus

Although the selection and use of different provenances within a tree species geographical distribution is an established practice in forestry, the same cannot be said for urban forestry. Understanding provenance-specific responses is crucial for selecting suitable planting materials to enhance urban forest resilience under environmental changes. Therefore, the purpose of this work, through the setting of two pot trials, was to a) assess the growth, physiology and phenology, during the entire growing season, of northern, central and southern Italian provenances of two species used in urban contexts across Europe, Q. robur (five provenances) and A. pseudoplatanus (four provenances); b) test if the provenance influences the physiological response to water stress and subsequent rewatering. The study represents an innovative effort to implement a forestry approach to addressing new challenges in urban environments. We observed a significant impact of provenance on phenology, height and biomass, encompassing both root- and shoot-system components, particularly evident in A. pseudoplatanus. Regarding water stress trials, A. pseudoplatanus plants from north Italy and Q. robur plants from a central Italy site, showed a higher tolerance to water stress than other provenances. The physiological mechanisms underpinning drought tolerance were revealed by the examination of leaf traits and plant nutritional status, underscoring the possibility of applying useful measurements like whole plant cuticular conductance (g_{min (plant)}) analysis to identify, in the nursery, seedling provenances that are potentially tolerant to drought. Our results help to inform decision-making policies and green planners to enhance the resilience and ecological function of urban green spaces.