The influence of elevated CO2 and O3 concentrations on Scots pine needles: changes in starch and secondary metabolites over three exposure years.

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.