Volatile emissions of six New Zealand fern species in response to physical damage and herbivory

Volatile compounds (scents) play an important role in mediating ecological interactions between plants and other organisms, including defence against biotic and abiotic stressors, such as herbivory or physical damage. Seed plants respond to wounding and herbivory by changing their volatile emissions and producing complex blends of compounds; this process is mediated by the phytohormone jasmonic acid (JA) that acts as a signalling molecule activating plant defence pathways. Exogenous application of JA can mimic the plant’s responses to herbivory and is used in agriculture to enhance plant defences. Although this phenomenon has been well documented for seed plants, our knowledge on non-seed plants is scarce, leading to question whether the observed patterns are ubiquitous to all vascular plant species. This study aimed to characterise the volatile emissions of six native New Zealand fern species (Cyathea dealbata, Cyathea medullaris, Dicksonia squarrosa, Asplenium bulbiferum, Asplenium oblongifolium, and Microsorum pustulatum), and explore their changes in response to physical damage, exogenous application of JA, and herbivory. Physical damage caused a significant increase in volatile emissions, with odour blends dominated by green leaf volatiles (as observed in seed plants); whereas JA application only caused a moderate increase in volatile release and (unlike seed plants) did not produce a substantial increase in terpenoid emission. Compounds (E)-2-hexene and (E)-2-pentenol were unique to the headspace of herbivore-damaged plants, indicating that ferns may have specific responses to herbivory. This work suggests that changes in volatile emissions are common responses to biotic and abiotic stress in vascular plants, but prompts further research to elucidate the signalling and regulatory mechanisms in ferns.