Wood hydraulic and mechanical properties induced by low water availability on two ornamental species Photinia×fraseri var. Red Robin and Viburnum opulus L.

In urban environments, trees are often faced with limiting physical factors at epigeous and hypogeum levels. These factors include poor air quality, and water and soil pollution that may differ substantially from the natural environment. When we consider the term “stress inducer,” this is meant as a limiting factor for the plant’s growth and development. While studies on urban climate and floristic analyses have often been published, studies on the physiological performance and growth of trees in urban sites are rather scarce. They are often in contradiction with the general opinion of the growth’s constraint. Generally, it is recognized that urban soils are made of poor landfill materials hampering soil water retention. Often, the soil is sealed by asphalted surfaces that prevent rain infiltration. Nevertheless, there is a gap of information to support the hypothesis by which such conditions determine plant water stress. This study will analyze the water relations and the performance of photosynthesis of Quercus ilex exemplars growing in three different conditions of urban green areas (urban park, outskirt/countryside and urban road) in the city of Florence (Italy) conducted in . The analysis and study was performed in the year 2002. Results have evidenced a decline in Pn in all three sites but a certain capacity of holm oak to acclimate to the worst site in terms of water relations, elasticity of tissues and in photosynthesis efficiency that .was higher in the urban road at the beginning of summer