The entangled dynamics of eucalypt leaf and flower volatile emissions

Eucalypts (including Angophora, Corymbia, Eucalyptus) comprise a large and hyper-diverse group of ecologically important trees providing habitats for many forest dependent species. Eucalypts synthesize a plethora of specialized metabolites that moderate biotic and abiotic interactions. Until now, studies on eucalypt volatile organic compounds (VOCs) have primarily focused on isoprene and monoterpenoid emission from forest plantations. As a result, little is known about the volatile profile of adult eucalypt trees under natural conditions. Here we present an in-depth study of leaf and flower branch volatile emissions from mature trees of nine eucalypt species in south-eastern Australia. VOCs were captured using a non-invasive, dynamic flow-through enclosure technique enabling volatile collection into adsorbent cartridges, analyzed by GC-MS. For comparison, terpenoid extracts were also analyzed. Complex emission profiles composed of more than 100 different VOCs were recorded, including isoprene, mono- and sesquiterpenoids, and benzenoids. Emission profiles from eucalypts were highly species-specific, tissue dependent, diurnally regulated and affected by environmental conditions. The composition of stored terpenoids did not mirror the emission profiles, supporting differential regulation of formation, storage and emission of terpenoids. These results provide important knowledge about the entangled dynamics of eucalypt volatiles, and have wider implications for predictions of volatile emission from eucalypt forests and plantations.