Chemotype diversity of foliar volatile emissions in Cork oak suggests independent geographic variations in quality and quantity

Knowledge of the intraspecific variability of volatiles produced by plants is central for estimating their fluxes from ecosystems and for understanding their evolution in an ecological and phylogenetic context. Past studies suggested that leaf volatile emissions from Cork oak ( Quercus suber L.) exhibit a particular high degree of qualitative and quantitative polymorphism. However, the extent of inherent emission variability across its range is not known.

We investigated leaf emissions and ecophysiological variables of 241 Cork oak seedlings from ten provenances. To minimize environmental influences, emissions were determined at 30 °C and saturating light on seed-grown saplings of similar age grown under the same conditions. All individuals, except for three apparent non-emitters, released the same five monoterpenes at a rate of 2559 ± 120 ng m ^-2 s ^-1 . Northern provenances tended to have higher mean emission rates and lower photosynthetic rates than southern populations, resulting in significant differences in their apparent carbon losses by volatile emissions. Independently, the emission composition varied discontinuously among individuals according to three distinct chemotypes, indicating inherent differences in the activity of two types of monoterpene synthases: one producing α-, β-pinene and sabinene, and the other limonene (plus myrcene as a by-product). Chemotype frequencies differed among provenances, particularly between South-Eastern Mediterranean and South-Western Atlantic provenances. Regarding ecophysiological leaf traits, we found no significant difference between chemotypes.

The study confirms that Cork oak is a strong monoterpene emitter, showing independent intraspecific variability in emission quality and quantity, with non-emitters being rare. Comparison of the emission variability with those reported for other oak species suggests that an ancestral Pinene/sabine chemotype has diversified within the oak subgenus Cerris during its radiation. This diversification is less pronounced in Cork oak than in other sympatric oaks, possibly due to differential fragmentation and expansion of their ranges in the past.