Long-term dynamics of BVOC production, storage and emission in boreal Scots pine

Abstract

Plants synthesise thousands of biogenic volatile organic compounds (BVOCs) as part of their secondary metabolism. Scots pine (Pinus sylvestris) particularly produces monoand sesquiterpenes, which are mainly stored in oleoresin in resin ducts. In this study, the monoterpene emission rate from stems was found to increase as a function of increasing resin pressure, which was positively correlated with the air temperature and foliage transpiration rate.Monoterpene synthase activity describes the maximum monoterpene production potential. The seasonal cycle and needle age were observed to explain the majority of the variation in needle monoterpene synthase activities, monoterpene storage pools and monoterpene emissions from shoots. Variation in the monoterpene concentration between seasons, different needle age classes and different trees was observed to be minor. Monoterpene synthase activity was higher in <1-year-old needles compared to older ones. Within a single tree, the compound-specific composition of monoterpene synthase activities and monoterpene storages was not reflected in the composition of emissions. For example, the share of δ-3-carene was substantially higher in the emissions than in the storage pools and synthase activities.An automated enclosure measurement system including a proton transfer reaction mass spectrometer was utilized to follow the VOC emissions from the woody compartments of trees over several years. This was the first study to quantify such emissions for an extended period. Scots pine stems were observed to emit monoterpenes and methanol into the ambient air. The fluxes displayed a seasonal cycle: methanol emissions were highest in the midst of the growing season, whereas monoterpene emissions peaked not only on the hottest summer days, but also in the spring when the photosynthetic capacity of trees recovered. The emissions of some monoterpenes exhibited distinct diurnal patterns in their enantiomeric compositions. The above-canopy air terpene concentrations reflected the emission rates from trees, the atmospheric reactivities of the compounds, the tree species composition of the measurement site and the abundances of different tree chemotypes.

Scots pine resin and BVOC emissions in relation to tree water dynamics

“…Abiotic stresses may also affect the emissions from stem: when subjected to drought, total monoterpene emissions from the stem of lodgepole x jack pine hybrids increased (Lusebrink et al 2013). Including the stem BVOC emissions into the context of the whole stand BVOC emissions for the first time, Vanhatalo (2018) calculated that the unwounded stem of Scots pine (Pinus sylvestris) trees contributed approximately 2% of the total stand BVOC emissions, while the foliage made up the largest part. Although 2% is a small proportion, omitting it will cause a bias when calculating emission sums over longer periods.…”

“…Measurements on the short and long-term VOC emission dynamics from tree stem are quite sparse. Temperature has been reported to drive the emissions of monoterpenes and methanol from pine stem at least at a daily scale (Vanhatalo 2018;Staudt et al 2019). However, at a longer time scale the effect may be different: Staudt et al (2019) reported largest monoterpene emissions from Maritime pine (Pinus pinaster) stem during humid rather than warm days.…”

“…The continuous measurements of VOC emissions from both Scots pine shoots and stem were based on a chamber system where chambers attached around shoots, stem and soil are cyclically measured and flushed (Kolari et al 2009(Kolari et al , 2012Aalto et al 2014;Aalto 2015;Vanhatalo et al 2015;Vanhatalo 2018). The chambers used in this study consisted of dynamic shoot chambers (study IV), steady state stem chambers (studies I, III and IV) and dynamic stem chambers (study III).…”

“…In addition, measurements on transpiration were used to analyse the effect of transport on the emissions of OVOCs (studies III and IV) and measurements on carbon dioxide (CO2) efflux from the stem were used to describe the metabolic activity in stem (study III). Transpiration was measured by the shoot chamber system described above (section 3.4.1) and by Kolari et al (2012), and stem CO2 flux using the stem chambers described above (section 3.4.1) and by Vanhatalo (2018). For analysis of water and CO2 concentrations, the sample air from the chambers was drawn to a URAS 4 infrared light absorption gas analyser (Hartman and Braun, Frankfurt am Main, Germany) or to a Li-840 A gas analyser (Li-Cor, Lincoln, NE, USA).…”

“…At the top, diffusion through thin bark is fast, and the xylem sap already may have high concentrations of OVOCs, enhancing their release. The top part of the stem is also more active (Vanhatalo 2018) and more exposed to the changes in temperature, contributing to higher emissions.…”