GROWTH AND REPRODUCTION OF APHIDS AND LEVELS OF FREE AMINO-ACIDS IN SCOTS PINE AND NORWAY SPRUCE IN AN OPEN-AIR FUMIGATION WITH OZONE

To estimate the susceptibility of conifer seedlings to aphids under fu ture tropospheric ozone levels, Scots pine (Pinus sylvestris L.) and N orway spruce (Picea abies (L.) Karst.) seedlings were exposed to ambie nt and elevated ozone levels in an open-air exposure system. Growth an d reproduction of the aphids Schizolachnus pineti and Cinara pinea on Scots pine and Cinara pilicornis on Norway spruce were monitored. Leve ls of free amino acids in foliage and young shoots were used as indica tors of host plant quality. In elevated treatment plots the ozone dose s were between 1.2 and 1.7 times the dose in ambient plots in 1990-93. Half of the seedling material in 1992-93 was subjected to nitrogen fe rtilization treatment to evaluate the effects of increased N depositio n. In 1990, population density of S. pineti on pine did not differ bet ween ambient and elevated ozone treatments during growing season, but remained higher in the elevated ozone plot than in the ambient plot at the end of the growing season. This was associated with elevated leve ls of glutamic acid in foliage. In August 1992, the numbers of S. pine ti were consistent between the two ambient ozone plots, but deviated h ighly between the two ozone-fumigated plots. Glycine concentration in pine foliage was elevated by ozone, but free amino acid concentrations were not related to aphid performance. In 1993, ozone and nitrogen di d not significantly affect the relative growth rate (RGR) of S. pineti or C. pinea nymphs on Scots pine, but glutamic acid concentration in foliage was increased by nitrogen fertilization. On Norway spruce, fec undity of C. pilicornis females was higher in elevated ozone treatment , but RGR of nymphs was not affected in 1992. In 1993, RGR of C. pilic ornis nymphs was increased by nitrogen fertilization in June, but not affected by ozone. Nitrogen fertilization increased the levels of tota l free amino acids, aspartic acid, glutamic acid and proline in elonga ting shoots of Norway spruce, and ozone reduced the concentrations of valine and gamma-butyric acid. Our results suggest that availability o f nitrogen from soil has a stronger impact on the concentrations of fr ee amino acids in conifer seedlings than ozone. Some episodes of high ozone concentration may increase free amino acids in foliage. Aphid re sponse to ozone was extremely variable, in agreement with previous lab oratory experiments. The expected 20-70% increase in ambient concentra tions of tropospheric ozone may in some occasions enhance aphid perfor mance on Scots pine and Norway spruce seedlings, but in most cases the ozone effect on the susceptibility of conifer seedlings to sucking in sect pests is not important.