Responses of spruce seedlings (Picea abies) to exhaust gas under laboratory conditions - I - plant-insect interactions

The effects of motor vehicle exhaust gas on Norway spruce seedlings (Picea abies (L.) Karst) and plant-insect interaction of spruce shoot aphid (Cinar a pilicornis Hartig) was studied. The exhaust gas concentrations in the fum igation chambers were monitored and controlled by measuring the concentrati on of nitrogen oxides (NOx) with a computer aided feedback system. The conc entrations of major exhaust gas components (black carbon [BC], fine particl es, VOCs and carbonyl compounds) in the chamber air were also measured. Rep onses of Norway spruce seedlings to a 2 and 3-week exhaust gas exposure and subsequent performance of spruce shoot aphid were studied using realistic exposure regimes; 50, 100 and 200 ppb NOx. The feedback control system base d on NOx concentrations proved an adequate and practical means for controll ing the concentration of exhaust gases and studying plant responses in cont rolled environment chambers. The exhaust exposure resulted in increased con centrations of proline, glutamine, threonine, aspartic acid, glycine and ph enylalanine and decreased concentration of arginine, serine, alanine and gl ycine in young needles. No changes in soluble N concentrations were observe d. The results are interpreted as a stress response rather than use of NOx as a nitrogen source. No changes in total phenolics and only transient chan ges in some individual terpene concentrations were detected. The exhaust ga s exposure stressed the exposed seedlings, but had no significant effect on N metabolism or the production of defence chemicals. Aphid performance was not significantly affected. Soluble N, secondary metabolism and aphid perf ormance were not sensitive to exhaust gas exposure during shoot elongation in Norway spruce. (C) 1999 Elsevier Science Ltd. All rights reserved.