SEASONAL VARIATION IN THE VOLATILE TERPENOIDS OF JUNIPERUS SCOPULORUM (CUPRESSACEAE)

Abstract

Fifteen trees in a natural population of Juniperus scopulorum Sarg. were sampled at 4‐week intervals throughout a year and the terpenoid constituents were extracted from the foliage. Several environmental variables were measured. Correlations with changes in volatile oil composition (computed as both relative percentages and as weights) were examined. Significant seasonal variations were discovered in both the relative percentage and weight data. These seasonal changes in the volatile oil composition were correlated with linear growth, temperature, yield of volatile oil, and dry weight of foliage. Seasonal variation in the terpenoids computed on a weight basis was found to be greater than the seasonal variation of the terpenoids computed as relative percents of the total oil. Evidence is presented which indicates that there is no stable period to sample on a weight basis, but sampling in the late fall and winter periods minimizes variation in the relative percentage data. The use of relative percentage data is thus encouraged for chemosystematic studies.