Isoprenoid emissions of Quercus spp. (Q-suber and Q-ilex) in mixed stands contrasting in interspecific genetic introgression

Among oak species, Quercus ilex is classified as a monoterpene emitter and Q. suber is mainly known as a nonisoprenoid emitter. The extent and origin of this diversification is unknown. We examined intra- and interspecific emission variability in two mixed stands which differed in their level of hybridization and reciprocal genetic introgression based on variations in cytoplasmic (chloroplast DNA) and nuclear (allozyme) markers. At both sites all trees identified as Q. ilex, or as recent descendants from Q. ilex x Q. suber hybrids, emitted monoterpenes. Of Q. suber trees (genetically introgressed or not by Q. ilex), 91% were also monoterpene emitters, and the remainder nonemitters. One tree identified as a Q. canariensis x Q. ilex hybrid emitted both isoprene and monoterpenes. Compared with Q. ilex, the standard emission rate of Q. suber was higher in summer and lower in autumn. Both species emitted the same monoterpenes, proportions of which showed significant intra- and interspecific variability. The results suggest that Q. suber populations in the French Mediterranean intrinsically emit monoterpenes, and that gene flow between oak species contributes to diversification of emission signatures.