INTERACTIONS BETWEEN EXPOSURE TO O-3 AND NUTRIENT STATUS OF TREES - EFFECTS ON NUTRIENT CONTENT AND UPTAKE, GROWTH, MYCORRHIZA AND NEEDLE ULTRASTRUCTURE

The responses of Norway spruce and Scots pine to the effects of increased O-3 and Ca or Mg deficiency stress, singly and in combination, for two growing seasons, were investigated in this study. The combination of open-air exposure to O-3 concentrations of 1.3-1.6 times higher than ambient, and an inadequate supply of Ca or Mg, did not affect root uptake and leaching of minerals from the needles of 3-yr-old seedlings, indicating that they had not developed severe nutrient deficiency. However, concentration of N decreased in the 1-yr-old needles of seedlings exposed to O-3. The height of the new shoots was promoted without an increase in shoot dry weight, which together with stimulated mycorrhiza development and decreased shoot-to-root radio indicated allocation of carbon from shoots to roots as an early effect of low-level O-3 exposure. Although the ultrastructural study did not reveal clear O-3 related injuries in cells, starch accumulated in chloroplasts of the fumigated seedlings grown with adequate, but not with deficient nutrients. The outcome of this study suggests that in medium-term exposure of conifer seedlings to low concentrations of O-3 and nutrient deficiency, stress can be tolerated by activated defence metabolism and compensation reactions, but adverse effects may be apparent in long-term continuous exposure.