Combined effects of ozone and nitrogen on secondary compounds, amino acids, and aphid performance in Scots pine

Combined effects of O-3 and N supply on Scots pine (Pinus sylvestris L,) we re studied in two separate growth chamber experiments exposing seedlings to 0, 0.075, 0.15, and 0.3 mu L/L of O-3 during 8 h/d, 5 d/wk for a period of 5 wk, Seedlings were fertilized with low, medium, and high levels of N. Oz one and N availability affected concentrations of several primary and secon dary metabolites, More changes on metabolites were detected in Exp, 1 (with seedlings ceasing their annual growth) than in Exp. 2 (with seedlings acti vely growing). Overall, high O-3 exposure levels significantly decreased co ncentrations of monoterpenes and increased concentrations of resin acids. C oncentrations of total phenolics were not affected by O-3 exposure. Mostly lower concentrations of monoterpenes and resin acids were found at a medium N-fertilization level than at low and high N-fertilization levels, while t otal phenolic concentration decreased by enhanced N availability. In Exp, 1 , significantly elevated concentrations of free amino acids were found at O -3 concentration of 0.3 mu L/L, Nitrogen availability did not have remarkab le effects on amino acid concentrations. in Exp. 1, both O-3 and N had a si gnificant effect on the MRGR of the aphid Schizolachnus pineti. In Exp. 2, the weight of the females and nymphs and the total number of reproduced nym phs were significantly affected by O-3 and N, Only a few interaction effect s were found, suggesting that the N supply does not significantly modify O- 3-induced effects on studied primary and secondary compounds and aphid perf ormance in Scots pine seedlings.