Isoprenoid emission in hygrophyte and xerophyte E uropean woody flora: ecological and evolutionary implications

Abstract

Aim The relationship between isoprenoid emission and hygrophily was investigated in woody plants of the I talian flora, which is representative of E uropean diversity. Methods Volatile isoprenoids (isoprene and monoterpenes) were measured, or data collected from the literature, for 154 species native or endemic to the M editerranean. The E llenberg indicator value for moisture ( EIVM ) was used to describe plant hygrophily. Phylogenetic analysis was carried out at a broader taxonomic scale on 128 species, and then refined on strong isoprene emitters ( S alix and P opulus species) based on isoprene synthase gene sequences ( I sp S ). Results Isoprene emitters were significantly more common and isoprene emission was higher in hygrophilous EIVM classes, whereas monoterpene emitters were more widespread and monoterpene emission was higher in xeric classes. However, when controlling for phylogeny, isoprene emission was not associated with EIVM , possibly due to the large presence of Salicaceae among hygrophilous isoprene emitters. Moreover, the distribution of isoprene emitters among EIVM classes was not related to I sp S ‐based phylogenesis in P opulus and S alix , suggesting that the gene has not undergone evolution linked to ecological pressure. In contrast, the monoterpene emission pattern is independent of phylogeny, suggesting that the evolution of monoterpenes is associated with transitions to more xeric habitats. Main conclusions Our results reveal an interesting ecological pattern linking isoprenoids and water availability. We suggest that isoprene is a trait that: (1) evolved in plants adapted to high water availability; (2) is replaced by more effective protection mechanisms, e.g. more stable isoprenoids, in plants adapting to more xeric environments; and (3) being strongly constrained by phylogeny, persists in S alicaceae adapted to more xeric environments.

Bibliographic Information