Calluna vulgaris volatile emissions suggest varying anti-herbivore defence strategies with plant ontogeny

Abstract

ABSTRACT Background Calluna vulgaris (heather) is native to Europe, where it dominates several plant communities, but is invasive in countries like Australia and New Zealand (NZ). In its native ranges, including the United Kingdom (UK), heather provides habitat to arthropods of several feeding guilds and recent studies in its invaded and native ranges show that this plant is a prolific producer of volatile organic compounds (VOCs). These defensive metabolites can modify the behaviours of neighbouring plant and insect species. However, differences in VOC emissions between growth stages (ontogeny) have not yet been explored. Aims The aim of this study was to explore the role of plant growth stages (pioneer, building and mature) and arthropods on VOC emissions of heather plants on a managed stand in Scotland during the summer season. Methods We applied the contact insecticide deltamethrin to exclude arthropods from half of the tested plants for each growth stage, collected above-ground volatiles from plants in each treatment, and analysed them using gas chromatography – mass spectrometry (GC-MS). Data were statistically analysed using sparse partial least square discriminant analysis (sPLS-DA) and general linear models (GLM). Results Results showed differences in volatile emission between growth stages, whereas the effect of arthropod removal was only observed for plants at the building stage. The results suggest that heather plants display different defence strategies as they mature, showing high phenotypic plasticity. Pioneer plants released fewer, ubiquitous compounds in relatively high amounts, building-unprayed plants were the most prolific VOC emitters showing herbivore-induced responses, and mature plants released a higher number of compounds but not in higher quantity than building plants. Thus, mature plants possibly rely more on mechanical and structural defences. Conclusion: These results highlight the complex and changing nature of heather’s volatile emissions during plant ontogeny and contribute to understanding the chemical ecology of heather in heathland ecosystems.