Effects of drought and canopy ozone exposure on antioxidants in fine roots of mature European beech (Fagus sylvatica)

We quantified ascorbate, glutathione and α-tocopherol in fine roots of mature Fagus sylvatica L. under free-air canopy ozone (O 3 ) exposure (twice ambient O 3 concentration, 2×[O 3 ]) during two growing seasons that differed in the extent of summer drought (exceptional drought year 2003, average year 2004). This design allowed us to test whether O 3 exposure or drought, or both, affected root antioxidants during the growing season. In both years, root ascorbate and α-tocopherol showed a similar relationship with volumetric soil water content (SWC): ascorbate concentrations on a root dry mass basis increased from about 6 to 12 μmol g −1 when SWC dropped from 25 to 20%, and a-tocopherol increased from 100 to 150 nmol g −1 at SWC values below 20%. Root glutathione showed no relationship with SWC or differences between the dry and the average year, but it was significantly and consistently diminished by 2×[O 3 ]. Our results were inconclusive as to whether shoot-root translocation of glutathione or glutathione production in the roots was diminished. Phloem glutathione concentrations in the canopy remained constant, but reduced transport velocity in the phloem and, as a consequence, reduced mass flow of glutathione cannot be ruled out.