Essential oil content of Rhododendron tomentosum responds strongly to manipulation of ecosystem resources in Arctic Alaska

The essential oils of the widely distributed boreal/Arctic dwarf shrub, Rhododendron tomentosum ssp. subarcticum (Harmaja) G.D. Wallace, have important ecological, cultural, medicinal, and commercial roles. To understand the relationship between resource limitation and essential oil content of this species we measured the amount and diversity of terpenes from shoots of plants exposed to a 14-year ecosystem resource manipulation experiment in Arctic Alaska. Treatments tested interactive effects of nitrogen (N) and phosphorus (P) addition, warming and N + P fertilization, and shading and N + P fertilization. The controls and NP fertilization had the highest essential oil content, whereas shading and P addition had less than 20% of the control content. Warming reduced essential oil content to <65% of that of the controls. Essential oil components varied greatly among the treatments, with significant differences in the expression of specific essential oil components. Large changes in plant community composition and ecosystem structure in response to treatments likely played a large role in the response of R. tomentosum. Our data suggest that resource changes in response to climate warming and its secondary effects on light and nutrient availability have the potential to change the profiles of essential oils in R. tomentosum, with important ecological and cultural impacts.