[eng] Plants, as sessile organisms, have developed complex strategies that allow them to evolve and interact with biotic and abiotic environmental factors. In addition to floral display and providing nutritional rewards, plants synthesise and emit a wide range of volatile organic compounds (VOCs) that perform various physiological and ecological functions. The chemical attraction of pollinators, allelopathic phenomena or the synthesis of toxic substances as a defence mechanism against herbivores are some of VOCs' most distinguished ecological functions.
VOCs can be synthesised in different plant tissues by complex and diverse physiological processes. In addition, a large temporal and spatial variability of VOCs emission rates has been corroborated due to the complexity of internal (genetic and biochemical) and external (abiotic and biotic) factors that regulate them. These scent mixtures allow plants to provide detailed information about their physiological and phenological state (flower condition, herbivore attack, microbial infection, available floral reward, etc.), which can be processed by other organisms, both beneficial and detrimental, that interact directly or indirectly with them.
This thesis aims to contribute to the knowledge of the Balearic flora, from a biochemical perspective, by studying the volatile profiles, using different extraction and analysis techniques, of a group of Mediterranean species selected to consider and evaluate various ecological aspects.
The first chapter of the thesis contributes to the knowledge of the strategies developed by rupicolous species against invertebrate predators. Clinopodium rouyanum (Briq.) Govaerts is a species endemic to Mallorca (Balearic Islands), in danger of extinction (VU), which grows between 900-1400 m. For this species, the micromorphological characteristics of green parts were described by scanning electron microscopy, essential oils were identified by SDE distillation, and VOCs emitted from green parts, whole flowers, and isolated corollas by HS-SPME-GC-MS, as well as internal volatiles from corolla tubes by ST-TD-GC-MS. Finally, the deterrent effects of essential oils and VOCs emission against invertebrates were evaluated. From an ecological perspective, we conclude that the composition of essential oils and VOCs emitted by C. rouyanum are key to its defence against invertebrate herbivores, and knowledge of these could contribute to the conservation of this endangered species.
The variety of angiosperm floral forms and the diversity of floral scents have been described as evolutionary characteristics defining their interactions with floral visitors. In the second chapter, we identify and analyse, by HS-SPME-GC-MS, the floral VOCs emitted by two sympatric and asynchronous climbing shrub species: Clematis cirrhosa L. and C. flammula L. We documented floral visitors and tested the degree of pollinator dependence on the reproductive success of the plants as a function of floral characteristics (shape and arrangement), floral phenology, scent and flowering time of each. The flowering of these species during periods of increased stress for pollinators due to the low availability of flowering species is essential for the survival of an important part of the pollinating entomofauna.
The third chapter focused on plant chemistry's taxonomic and phylogenetic value and the recent use of VOC in taxonomic studies. Floral VOCs were identified for two species of the genus Rhamnus (Rh. alaternus L. and Rh. ludovici-salvatoris Chodat.) and for the hybrid between these taxa (Rh. Xbermejoi Fraga & Rosselló). The volatile profiles obtained showed significant quantitative and qualitative differences, which corroborated their chemotaxonomic value as a discriminant character between closely related taxa.
Finally, in the fourth chapter, VOCs emitted by whole flowers were captured and identified by HS-SPME-GC-MS from two Mediterranean synchronous asparagus species: Asparagus acutifolius L. and A. albus L. For these species, different natural populations of the Balearic Islands were monitored, and their floral phenology, pollinators and reproductive success were studied. In addition, the phenomenon of gynodioecy in A. acutifolius was discussed. Finally, the evolution of scent and diversification of floral VOCs between sympatric and synchronous species is an important biological strategy to coexist in an ecosystem where competition for pollinators may be a key factor for reproductive success.
Thus, the present thesis provides new knowledge on different roles played by VOCs in a representation of Mediterranean plants, as well as their impact on interactions with other organisms and their potential application in chemotaxonomy.