Ecophysiological and biochemical traits of Quercus ilex trees growing under urban stress conditions

The metabolic regulations of evergreen Mediterranean Quercus ilex trees growing at extra-urban and urban sites with different percentages of surrounding impervious pavements and distance to major traffic roads were investigated at the peak of the summer drought season. Plants from extra-urban site experienced lower water stress due to a fine regulation of reactive oxygen species (ROS, concomitant rise of anion superoxide and hydrogen peroxide content, +55 and +44%), abscisic acid and water soluble carbohydrates (+111 and +9%). The level of ROS was kept under the injury threshold by both enzymatic and metabolic antioxidants. Plants from the sub-urban site followed a different strategy, with a lower production of ROS and the concomitant reduction in phenols and carotenoids. Despite these differences, indications for stress induced injury were not observed in any of the sites. Our work shows new relations between urban stress conditions and metabolic regulations of trees growing under such harsh environments.