Effects of ozone (O) and ethylenediurea (EDU) on the ecological stoichiometry of a willow grown in a free-air exposure system.

Ground-level ozone (O) concentrations have been elevating in the last century. While there has been a notable progress in understanding O effects on vegetation, O effects on ecological stoichiometry remain unclear, especially early in the oxidative stress. Ethyelenediurea (EDU) is a chemical compound widely applied in research projects as protectant of plants against O injury, however its mode of action remains unclear. To investigate O and EDU effects early in the stress, we sprayed willow (Salix sachalinensis) plants with 0, 200 or 400 mg EDU L, and exposed them to either low ambient O (AOZ) or elevated O (EOZ) levels during the daytime, for about one month, in a free air O controlled exposure (FACE); EDU treatment was repeated every nine days. We collected samples for analyses from basal, top, and shed leaves, before leaves develop visible O symptoms. We found that O altered the ecological stoichiometry, including impacts in nutrient resorption efficiency, early in the stress. The relation between P content and Fe content seemed to have a critical role in maintaining homeostasis in an effort to prevent O-induced damage. Photosynthetic pigments and P content appeared to play an important role in EDU mode of action. This study provides novel insights on the stress biology which are of ecological and toxicological importance.