High chemodiversity in the structural and enantiomeric composition of volatiles emitted by Kermes oak populations in Southern France

Abstract

Investigating the intraspecific variability of volatiles produced by vegetation is of fundamental importance in the understanding of their ecological roles and in correctly assessing their fluxes from vegetation covers. We characterized foliar emissions and CO2/H2O-gas exchanges from 80 seed-grown Kermes oak (Quercus coccifera L.) saplings originating from 4 populations located on a northeast–southwest transect in Southern France. Emissions of a large range of volatiles including chiral isomers were determined under environmentally controlled conditions by online and offline gas chromatography. All saplings emitted principally α-, β-pinene, sabinene, myrcene, eucalyptol, and limonene plus traces of other monoterpenes (MTs), sesquiterpenes, and isoprene. The enantiomers of α- and β-pinene were highly correlated with a predominance of the (+)-forms in the emissions. On average, the total isoprenoid emission rate was 772 ± 398 ng m−2 s−1. The compositional fingerprint varied in a discontinuous manner among individuals unrelated to the emission quantity and little influenced by season and leaf age. Cluster analyses revealed 4 main chemotypes plus 2 subtypes, which could be explained by a combination of 5 putative MTs synthases producing predominantly myrcene, limonene, eucalyptol, (+)-pinenes, and sabinene plus (−)-pinenes, respectively. The frequency of chemotypes, the average fraction of single volatiles and the ratios of pinene enantiomers were significantly different among populations without clear geographic or climatic cline. However, plants of one chemotype, which was most abundant in the population of the driest site, expressed an increased photosynthetic water use efficiency. Overall, the results revealed a marked ubiquitous chemical polymorphism in Kermes oak populations with similarities to that observed in other MT producing oak species, especially with its closely related and sympatric congener Holm oak.