Terpene deployment in Eucalyptus polybractea; relationships with leaf structure, environmental stresses, and growth

Terpene deployment was examined in a population of Eucalyptus polybractea (R.Baker) trees. Eucalyptus polybractea is a terpene-accumulating species, which stores terpenes in oil glands beneath the leaf surface. Using regression analysis, we showed that leaf thickness, measured as leaf mass per area (LMA), influenced terpene content, apparently through regulation of gland dimensions, and thus, gland volume. We also examined how environmental factors affected terpene content through regulation of both LMA, and therefore, storage capacity, and the supply of resources for terpene synthesis. Neither water stress, measured using carbon isotope ratios as an indicator, nor nutrient stress, measured as foliar nitrogen and phosphorus content, accounted for observed variation in either terpene content or LMA. Phenolic content, measured as a possible competing carbon sink, did not account for variation in terpene content, and variation in environmental stresses could not account for differences in growth rate. However, both terpenes and total carbon-based secondary metabolites (terpenes and phenolics) showed positive correlations with growth, suggesting plants gain a growth advantage by deploying greater amounts of secondary metabolites.