Emission of herbivore-induced volatile terpenoids from two hybrid aspen (Populus tremula x tremuloides) clones under ambient and elevated ozone concentrations in the field

Tropospheric ozone levels are continuously rising due to human activities in the 21st century. Although the phytotoxic impact of ozone on plants has been well documented, the effect of ozone on plant emissions has received little attention. We have conducted a field-based investigation utilizing two clones of hybrid aspen (Populus tremula L. xP. tremuloides Michx.) in a free-air ozone concentration enrichment (FACE) facility. The effects of chronic exposure to moderately increased concentrations of ozone on insect-induced terpene emissions by these trees were investigated. We used two herbivore species, Phyllobius piri, and Epirrita autumnata, both of which can reach outbreak levels on deciduous trees in Northern Europe. Our results indicated only very small changes in emissions due to increased ozone levels, but showed induction of some terpenes, particularly the monoterpene trans-beta-ocimene and the homoterpene (E)-4,8-dimethyl-1,3,7-nonatriene, in response to insect feeding. Here, we consider the positive aspects of conducting this type of study in the field and consider the possible influences of other field-based environmental factors.