Foliar antioxidant status of adult Mediterranean oak species (Quercus ilexL. and Q-pubescens Willd.) exposed to permanent CO2-enrichment and to seasonal water stress

Foliar antioxidants were measured in adult individuals of holm oaks (Quercu s ilex L.) and white oak (Q. pubescens Willd.) growing in the field either within the vicinity of natural CO2 springs or at a nearby control site unde r ambient CO2, which had been previously exposed to either daily irrigation or no irrigation. In oak trees permanently exposed to elevated CO2 the act ivities of antioxidant enzymes tended to be lower and the ascorbate pool wa s larger and more in reduced form, suggesting an attenuation of the oxidati ve risk in the CO2-enriched trees. In the enriched individuals of both spec ies, the imposition of water shortage significantly increased the size of t he glutathione pool and the total superoxide dismutase activity in a specie s-specific manner. Moreover, water-stressed trees exposed to elevated CO2 t ended to have higher catalase and ascorbate peroxidase activities than wate r-stressed control trees. Such changes may reflect the need for an enhanced compensatory effort when trees acclimated to elevated CO2 are exposed to o xidative stress-promoting environmental factors. such as water shortage. (C ) 2001 Elsevier Science Ltd. All rights reserved.