Variation in birch (Betula pendula) shoot secondary chemistry due to genotype, environment, and ontogeny

Plant secondary chemistry is determined by both genetic and environmental factors, and large intraspecific variation in secondary chemistry has frequently been reported. The heritability of specific tree secondary metabolites is, however, mostly unknown. We tested the effect of plant genotype, environment, and ontogeny on the variation in shoot secondary chemistry of juvenile and mature European white birches (Betula pendula). Phenolic compounds and triterpenoids were analyzed in 30 naturally regenerated 20-year-old parental trees and micropropagated plantlets that originated from 14 of those same parental trees, planted at four growing sites. Most of the variation for phenolic compounds was explained by differences between parental trees, whereas triterpenoids had a high variation both between parental trees and within the canopy of individual tree. The effect of ontogeny was strong for some individual compounds. In mature trees, the amount of triterpenoids was less than 1 mg/g (DW), whereas the concentration in juvenile plantlets was up to 64 mg/g (DW). Clonal plantlets and parental trees were generally quite similar in their phenolic contents, but there were significant differences for all analyzed compounds among clones. Environment had no significant effect on the accumulation of some compounds, whereas for others, a significant environmental effect and/or significant genotype by environment interaction was found. These results suggest that birch shoot secondary chemistry is under strong genetic control and that the environmental effects depend on the studied chemical trait.