Changes in the Essential Oil Composition in the Needles of Scots Pine (Pinus sylvestris L.) Under Anthropogenic Stress

Unfavorable anthropogenic factors, such as air pollution, lead to biochemical responses in trees. Changes in the amounts of secondary metabolites may be early indicators of invisible injuries. The aim of this study was to evaluate composition of the essential oils in the needles of Scots pine (Pinus sylvestris L.) growing in the areas affected by pollutant emissions of main factories in Lithuania: a nitrogen fertilizer factory (NFF), a cement factory (CF), and an oil refinery (OR). Totally, 14 pine stands were examined along transects from the factories (July 2005). Volatile components of the needles were extracted and analyzed by GC and GC/MS. Over 70 components of the essential oils were identified in current-year and 1-year-old needles. Along the CF transect for current-year needles, the percentage of diterpenes was decreasing with the increasing pH of the pine bark (r = -0.582; p < 0.05) or with the increasing concentration of SO(2) (r = -0.573; p < 0.05); for 1-year-old needles, the percentage of diterpenes was decreasing with the increasing pH of the bark (r = -0.534; p < 0.05). Along the OR transect, in both the current-year and 1-year-old needles, the percentage of diterpenes was decreasing with the increasing SO(2) (respectively, r = -0.773; p < 0.01; r = -0.486; p < 0.05); an opposite relation was true for sesquiterpenes (respectively, r = -0.751; p < 0.01; r = 0.785; p < 0.01). The view was different along the NFF transect. For current-year needles, the percentage of monoterpenes was decreasing with the increasing NH(3) (r = -0.669; p < 0.01); while the percentage of sesquiterpenes or oxysesquiterpenes was increasing with the increasing NH(3) (respectively, r = 0.540; p < 0.05 and r = 0.688; p < 0.01). For each transect, cluster analysis of the percentages of components of essential oils in the needles allowed us to distinguish the most contrasting stands according to the concentration of air pollutants. Current-year needles were more effective as indicators of the effects of pollution than 1-year-old needles in the case of the NFF and the OR transects, and both-aged needles were equally valuable in the case of the CF transect. The changes detected in the proportions of components of the essential oils in the needles of the trees affected by the industrial emissions may play a significant role in modifying the susceptibility of the pine stands to the biotic factors, and also may alter emissions of terpenes from the stands to the atmosphere.