Influence of elevated ozone and limited nitrogen availability on conifer seedlings in an open-air fumigation system: effects on growth, nutrient content, mycorrhiza, needle ultrastructure, starch and secondary compounds

Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies Karst.) see dlings were exposed to realistically elevated O-3 levels in open-air experi ments over three growing seasons. The total O-3 exposure doses were 1.2 x ( 1991), 1.5 x (1992) and 1.7 x (1993) ambient levels. During the 1992 and 19 93 growing seasons pine and spruce seedlings received two different levels of nitrogen supply. Effects on growth, mycorrhiza formation, needle ultrast ructure, primary and secondary compounds were studied. Ozone exposure had o nly slight effects on biomass production, growth height and nutrient conten t of studied conifers. Higher nitrogen availability improved growth of the seedlings and resulted in higher concentration of nitrogen in needles. In S cots pine O-3 exposure did not have effects on quantity of total mycorrhiza s and short roots, while higher nitrogen availability decreased quantity of mycorrhizas and short roots. In both tree species O-3 exposure induced O-3 -related ultrastructural symptoms, e.g. granulation and dark staining of th e chloroplast stroma in the needle mesophyll cells, at both nitrogen availa bility levels. Ozone exposure and nitrogen availability did not have signif icant effects on starch concentrations in either tree species. Concentratio ns of some individual terpenes were higher in O-3-exposed needles, while co ncentrations of individual and total resin acids, total phenolics and catec hins were not affected by O-3 exposure. Nitrogen availability did not have substantial effects on concentrations of monoterpenes. By contrast, concent rations of some individual and total resin acids were lower in pine needles and higher in spruce needles with higher nitrogen availability, while phen olic concentration in spruce needles decreased at higher nitrogen availabil ity. The results suggest that realistically elevated levels of O-3 in the f ield can have some negative effects on the mesophyll ultrastructure of coni fer needles, but carbon allocation to root and shoot growth and secondary m etabolites are not affected substantially.