QUANTIFICATION OF OZONE INFLUX AND APOPLASTIC ASCORBATE CONTENT IN NEEDLES OF NORWAY SPRUCE TREES (PICEA-ABIES L, KARST) AT HIGH-ALTITUDE

The objective of the present study was to investigate whether peak concentrations of ozone can deplete the apoplastic ascorbate pool of needles from Norway spruce trees (Picea abies I,, Karst,) and, thereby, contribute to damage to forest trees, Twigs of forest trees grown at high altitude (1950m above sea level; Mt Patscherkofel, Austria) were enclosed in situ in chambers and fumigated for 5.5 or 17h with ozone concentrations ranging from 60 to 798 nmolmol(-1). Adjacent branches were fumigated with filtered air, Ozone influx into the foliage ranging from 1.7 to 17 nmolm(-2)s(-1) had little effect on whole-needle ascorbate or glutathione contents, However, apoplastic ascorbate decreased by about 30% when the needles were exposed to environmentally relevant ozone concentrations and increased about 3-fold at higher ozone concentrations, This response suggests the induction of ascorbate as a protective system and may also be important under field conditions, Needles of spruce trees from high altitude that were exposed to chronically increased ozone concentrations contained significantly higher apoplastic ascorbate concentrations than needles from spruce trees from lower altitudes with lower mean atmospheric ozone concentrations, The results show that peak concentrations of ozone do not act in spruce via a depletion of the apoplastic ascorbate pool.