New Perspectives on CO2, Temperature, and Light Effects on BVOC Emissions Using Online Measurements by PTR-MS and Cavity Ring-Down Spectroscopy.

Volatile organic compounds (VOC) play important roles in atmospheric chemistry, plant ecology, and physiology, and biogenic VOC (BVOC) emitted by plants is the largest VOC source. Our knowledge about how environmental drivers (e.g., carbon, light, and temperature) may regulate BVOC emissions is limited because they are often not controlled. We combined a greenhouse facility to manipulate atmospheric CO2 ([CO2]) with proton-transfer-reaction mass spectrometry (PTR-MS) and cavity ring-down spectroscopy to investigate the regulation of BVOC in Norway spruce. Our results indicate a direct relationship between [CO2] and methanol and acetone emissions, and their temperature and light dependencies, possibly related to substrate availability. The composition of monoterpenes stored in needles remained constant, but emissions of mono-(linalool) and sesquiterpenes (β-farnesene) increased at lower [CO2], with the effects being most pronounced at the highest air temperature. Pulse-labeling suggested an immediate incorporation of recently assimilated carbon into acetone, mono- and sesquiterpene emissions even under 50 ppm [CO2]. Our results provide new perspectives on CO2, temperature and light effects on BVOC emissions, in particular how they depend on stored pools and recent photosynthetic products. Future studies using smaller but more seedlings may allow sufficient replication to examine the physiological mechanisms behind the BVOC responses.