We compared the foliar antioxidant status of native Agrostis stolonifera L. communities growing at two distinct CO2-enriched sites of geothermal origin (E) and at a control field location with normal CO2. Compared to the control, plants from both E-sites showed an increased size of the GSH pool, essentially due to enhanced GSSG levels, and a consequent decrease in the ratio between reduced and oxidised glutathione forms. Such differences were maintained and even enhanced in the vegetatively-propagated progenies of control and E-plants, grown under both greenhouse conditions and normal CO2 levels. The above results confirmed previous observations on native and crop plants exposed to elevated CO2. It is therefore suggested that changes in the glutathione redox balance might be of adaptive significance under conditions of permanent exposure to high CO2.