Highly diverse emission of volatile organic compounds by Sitka spruce and determination of their emission pathways

Abstract

The diversity of biogenic volatile organic compounds (BVOCs) emitted by Sitka spruce (Picea sitchensis) saplings, housed in a plant growth chamber, has been investigated using a combination of on-line (time-of-flight chemical ionisation mass spectrometry) and off-line (gas chromatography-mass spectrometry) measurement techniques. In total, 74 BVOCs were identified in the Sitka spruce emissions, considerably more than reported previously. Among the emitted BVOCs, 52 were oxygenated compounds, with piperitone (C₁₀H₁₆O), an oxygenated monoterpene, being the most abundant. Other prevalent emissions included isoprene, five monoterpenes (myrcene, β-phellandrene, δ-limonene, α-pinene, and camphene), cinnamaldehyde and camphor. Temperature and photosynthetic photon flux density (PPFD) were found to be the main drivers of emissions, with BVOCs exhibiting a range of responses to these factors. 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. During these cycles, all BVOCs showed clear diurnal patterns that were highly reproducible during consecutive days. The majority of the BVOCs emitted by Sitka spruce were found to originate from biosynthetic and pooled pathways simultaneously, with those from one sapling having a much lower contribution from the biosynthetic pathway. 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). Standard emission factors were calculated to be 17.29 μg g_dw⁻¹ h⁻¹ for piperitone, 6.3 μg g_dw⁻¹ h⁻¹ for isoprene and 0.93 μg g_dw⁻¹ h⁻¹ for monoterpenes, indicating that Sitka spruce is a strong BVOC emitter.