Sources of variation in concentration and composition of foliar monoterpenes in tamarack (Larix laricina) seedlings: Roles of nutrient availability, time of season, and plant architecture

The effects of foliage class, time of season, and nutrient availability on monoterpene composition and concentration were evaluated. In the first expe riment, we compared foliar monoterpenes of long shoots versus short shoots, which differ in age and origin, and differences due to nutrient availabili ty and time of season. Both the concentrations and compositions of these mo noterpenes were higher in the foliage of the long shoots. The only exceptio ns were the concentration of Delta-3-carene and the composition of beta-pin ene. Within a foliage class, the concentrations of seven monoterpenes and t he percentages of five monoterpenes changed over the season. Of these, almo st all declined, with the exceptions of beta-pinene and an unknown. Nutrien t availability significantly affected the concentration or composition of s ome monoterpenes, but only to a slight extent. beta-Pinene and the unknown increased with nutrient availability, whereas alpha-pinene and myrcene decr eased. A more comprehensive analysis of four foliage classes on a separate cohort of trees showed that all monoterpenes, except sabinene and terpinole ne, differed between foliage classes, but there were few general patterns. Overall, within-tree variation in tamarack monoterpenes related to foliage class and age appears more important than between-tree variation due to nut rient availability. These results suppport the view that products of mevalo nic acid biosynthesis, such as terpenes, do not follow predictions of the c arbon-nutrient balance and growth differentiation hypotheses. Our overall r esults show that individual hosts need to be considered as phytochemical mo saics when interpreting herbivore-plant interactions.