Boreal forest soil is a significant and diverse source of volatile organic compounds

Abstract

Abstract. Vegetation emissions of volatile organic compounds (VOCs) are intensively studied world-wide because oxidation products of VOCs contribute to atmospheric processes, but the quantities by which different species of VOCs are produced by soil, or how effectively belowground VOCs are released into the atmosphere from soil remains largely unknown. This is the first published study that measures belowground VOC concentrations at different depths in a podzol combined with simultaneous soil surface flux measurements in a boreal coniferous forest. More than 50 VOCs, dominated by monoterpenes 15 and sesquiterpenes, were detected in the air space in the soil during the two measurement campaigns. Organic forest soil was a significant monoterpene source as it contained fresh isoprenoid-rich litter, and the concentrations of monoterpenes were comparable to the VOC concentrations in the air above the coniferous forest. Belowground monoterpene concentrations were largely decoupled from forest floor monoterpene fluxes; thus, it seems that production processes and storages of VOCs partly differ from those VOCs that are simultaneously emitted from the soil surface. Relatively high isoprenoid concentrations were 20 measured under snow cover, which indicates that snow and ice cover hinders gas diffusion and causes belowground accumulation of VOCs when the activity of vegetation is very low.

Soil Uptake of Volatile Organic Compounds: Ubiquitous and Underestimated?

“…Until recently, attention has focused on the quantification of VOC emissions, which influence local air quality, as a result of ozone and particle formation, and climate, via complex contributions to climate‐aerosol feedbacks (Arneth et al, 2010). Vegetation is the primary source of biogenic VOCs to the atmosphere, but soils also contribute significant emissions, at least in specific situations, like the dry season in the Amazonas (Bourtsoukidis et al, 2018), permafrost thaw in the Arctic (Kramshøj et al, 2018), or shoulder seasons in boreal forest (Mäki et al, 2019). More recently, advances in instrumentation that have allowed for continuous measurements in situ have led to observations of bidirectional ecosystem VOC fluxes (Millet et al, 2018; Park et al, 2013) that have highlighted the importance of both emissions and deposition .…”

The role of soils in the regulation of air quality

“…signalling for synchronous activities such as sporulation in fungi [22], and can be detectable at local levels, e.g. boreal forests [23]. Emissions from plants (see §4b) and anthropogenic sources rather than direct emissions from soil are generally considered to be a greater concern for air quality itself.…”

Plant Secondary Compounds in Soil and Their Role in Belowground Species Interactions

“…Concentrations of PSCs can be high and persistent in the soil. For instance, mono-and sesquiterpenes released from pine needles, litter, and roots are detectable in forest soil throughout the year [18] and can reach high concentrations especially in topsoil but also lower mineral soil, being highest in late summer, and in the winter during snow cover [19]. Glucosinolates, produced by all cruciferous plants, are hydrolyzed in the soil to highly bioactive compounds, notably isothiocyanate, nitriles, and thiocyanate.…”

“…However, the concentration of VOCs from soil may be b10 μg m -3 , which is below the detection limit for head-space analysis. This limitation may be overcome with purge-and-trap methods recommended for analysis when concentrations are b200 μg kg -1 [113], which were recently applied for sampling isoprene, monoterpenes, and sesquiterpenes in forest soil [19].…”