Volatile organic compound fluxes from northern forest soils

Abstract

Emissions of biogenic volatile organic compounds (BVOCs) cool down the global climate via their impacts on aerosol and cloud formation. Climate change will likely have a major impact on BVOC fluxes from the biosphere, including soils, due to temperature-driven plant biosynthesis of volatile organic compounds (VOCs), compound volatility and microbial activity. Soils are a poorly quantified source of VOCs, where the diversity of driving factors creates high spatial and temporal variability in soil VOC fluxes. The aim of this study was to analyse the magnitude and variability of forest floor VOC fluxes, to determine the role of the boreal forest floor in the forest stand BVOC exchange and to estimate plant ecophysiological and microbiological processes, which drive forest floor VOC exchange. Forest floor VOC exchange was determined using a steady-state flow-through chamber technique coupled with mass spectrometry in the boreal and hemiboreal climates. We revealed that the boreal forest floor contributes significantly to forest stand fluxes, but its importance varies between seasons. The forest floor accounted only a few per cent of the total forest stand fluxes of monoterpenes in summer, while in spring and autumn it could be up to 90%. The forest floor VOC exchange was stable between years, while fluxes had clear seasonal dynamic. Monoterpenes and oxygenated VOCs originated from fresh litter, microbial activity, and ground vegetation VOC biosynthesis. Air inside soil layers was found to contain diverse compounds. Forest floor VOC fluxes varied strongly depending on climate and tree species. Atmospheric chemistry may be strongly affected by soils during periods when plant-related BVOC biosynthesis and fluxes are low. In the future, we need continuous and simultaneous VOC exchange measurements from forest floors and forest stands in various ecosystems and climate zones. The global budget for soil VOC emissions should also be defined based on existing studies.

Biogenic Volatile Organic Compounds in Arctic Soil: A Field Study of Concentrations and Variability With Vegetation Cover

“…Rinnan et al (2013) found similar compounds as in our study, for example, 1-octene, to be induced by mechanical disturbance of subarctic heath vegetation. Furthermore, an increase in microbial release of BVOCs caused by an increased input of labile C from damaged roots and microbial communities might also have taken place (Mäki, 2019). Future research is encouraged to take into consideration the disturbance from installation equipment when designing experiments.…”

“…Most research on sBVOCs has focused on emissions, measured either from excavated soil samples in laboratories (Bourtsoukidis et al, 2018; Kramshøj et al, 2018; Leff & Fierer, 2008) or from soil surfaces, with or without a litter layer, in the field (Asensio, Peñuelas, et al, 2008; Kramshøj et al, 2016). Only few studies have examined BVOC concentrations in the soil, and sampling methods are not well established yet (Albers et al, 2011; Mäki, 2019; Smolander et al, 2006). A major concern associated with sampling in the soil environment is that sampling procedures may cause disturbance that affects the measured concentrations (Van der Putten et al, 2001).…”