The role of low-level ozone exposure and mycorrhizas in chemical quality and insect herbivore performance on Scots pine seedlings

The effects of low-level ozone exposure and suppression of natural mycorrhi zas on the above-ground chemical quality of Scots pine (Pinus sylvestris L. ) needles and insect herbivore performance were studied in a two-year field experiment. Seedlings were fumigated with the ozone doses 1.5-1.7 times th e ambient, and natural mycorrhizal infection level was about 35% reduced in roots with fungicide propiconazole. On ozone-exposed seedlings the mean re lative growth rate (MRGR) of Lygus rugulipennis Popp. nymphs was lower than on ambient ozone seedlings, but Gilpinia pallida Klug sawfly larvae grew b etter on elevated ozone seedlings than on ambient ozone seedlings. MRGR of Schizolachnus pineti Fabr. and Cinara pinea L. aphid nymphs or Neodiprion s ertifer Geoffr. sawfly larvae or the oviposition of L. rugulipennis and N. sertifer were not affected by ozone exposure. Although ozone exposure did n ot affect total phenolics, total terpene, total or individual resin acid, t otal free amino acid, nutrient or sugar concentrations in needles, MRGR of L. rugulipennis positively correlated with total terpenes and MRGR of G. pa llida positively with total amino acids. In addition, ozone exposure increa sed serine and proline concentration and marginally also starch concentrati on in needles. When mycorrhizas were reduced with fungicide, only MRGR of L . rugulipennis nymphs increased, but performance of other insect herbivores studied was not changed. However, number of L. rugulipennis eggs correlate d positively with mycorrhizal infection level and also with total sugars. R eduction of mycorrhizas did not strongly affect the concentrations of analy sed compounds in needles, because only phosphorus and potassium and some in dividual resin acids were reduced by fungicide treatment. These results sug gest that low-level ozone exposure and moderately declined mycorrhizal infe ction do not drastically affect either the above-ground chemical quality of Scots pine seedlings or performance of studied insect herbivores.