Identification of volatile organic compounds emitted by Sitka spruce and determination of their emission pathways and fluxes

Abstract

Abstract. The biogenic volatile organic compounds (BVOCs) emitted by Sitka spruce (Picea sitchensis) trees, housed in a plant growth chamber, were characterised by a combination of on-line (time-of-flight chemical ionisation mass spectrometry) and off-line (gas chromatography-mass spectrometry) techniques. In total, 74 BVOCs were identified in the Sitka spruce emissions, 52 of which were oxygenated compounds, with piperitone (C10H16O), an oxygenated monoterpene, being the dominant emission. Other prevalent emissions included isoprene and five monoterpenes (myrcene, β-phellandrene, δ-limonene, α-pinene, and camphene). Temperature, photosynthetic photon flux density (PPFD) and stress were all found to alter the emission profiles, with different BVOCs exhibiting different responses. Three different plant growth cycles were used to identify the emission pathways (pooled or biosynthetic) for each BVOC, through determination of the relationships of the emission flux with temperature and with PPFD. The majority of the BVOCs emitted by Sitka spruce were found to originate from biosynthetic and pooled pathways simultaneously, with those from a stressed tree having a much lower contribution from the biosynthetic pathway than a healthy tree. Standardised emission fluxes (temperature 30 °C and PPFD 1000 µmol m-2 s-1) were calculated for all BVOCs using the appropriate standardisation model (pooled, biosynthetic or combined). Annual emission fluxes for all Stika spruce plantations in Ireland were determined for piperitone (8,200 tonne year-1), isoprene (13,000 tonne year-1) and monoterpenes (1,600 tonne year-1). At the current conditions of the Irish climate the annual BVOC flux for isoprene was found to exceed that for piperitone, although this is expected to change in a warming climate.