The influence of elevated CO₂ and O₃ concentrations on Scots pine needles: changes in starch and secondary...

Scots pine (Pinus sylvestris L.) trees, aged about 20 years old, growing on a natural pine heath were exposed to two concentrations of CO₂ (ambient CO₂ and double-ambient CO₂) and two O₃ regimes (ambient O₃ and double-ambient O₃) and their combination in open-top chambers during growing seasons 1994, 1995 and 1996. Concentrations of foliar starch and secondary compounds are reported in this paper. Starch concentrations remained unaffected by elevated CO₂ and/or O₃ concentrations during the first 2 study years. But in the autumn of the last study year, a significantly higher concentration of starch was found in current-year needles of trees exposed to elevated CO₂ compared with ambient air. There were large differences in concentrations of starch and secondary compounds between individual trees. Elevated concentrations of CO₂ and/or O₃ did not have any significant effects on the concentrations of foliar total monoterpenes, total resin acids or total phenolics. Significantly higher concentrations of monoterpenes and resin acids and mostly lower concentrations of starch were found in trees growing without chambers than in those growing in open-top chambers, while there were no differences in concentrations of total phenolics between trees growing without or in chambers. The results suggest that elevated concentrations of CO₂ might increase foliar starch concentrations in Scots pine, while secondary metabolites remain unaffected. Realistically elevated O₃ concentrations do not have clear effects on carbon allocation to starch and secondary compounds even after 3 exposure years.