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

Mari Mäki,Heidi Hellén,Jussi Heinonsalo,Jukka Pumpanen,Hermanni Aaltonen,Jaana Bäck

doi:10.1007/s11104-019-04092-z

Abstract

AimsVegetation emissions of volatile organic compounds (VOCs) are intensively studied world-wide, because oxidation products of VOCs contribute to atmospheric processes. The overall aim of this study was to identify and quantify the VOCs that originate from boreal podzolized forest soil at different depths, in addition to studying the association of VOC concentrations with VOC and CO2 fluxes from the boreal forest floor.MethodsThis is the first published study that measures belowground VOC concentrations at different depths in a podzol soil combined with simultaneous flux measurements from the boreal forest floor. The VOC concentrations were determined by sampling VOCs from air inside soil layers using the gas collectors and adsorbent tubes. Forest floor VOC fluxes were determined using a dynamic enclosure technique. All the VOC samples were analysed using a thermal desorption-gas chromatograph-mass spectrometer.ResultsMore than 50 VOCs, dominated by monoterpenes and sesquiterpenes, were detected in the air space in the soil during two measurement campaigns. The O-horizon was a significant monoterpene source, because it contained fresh isoprenoid-rich litter. 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 released from the forest floor. Both fluxes and concentrations of the monoterpenes and sesquiterpenes correlated with the CO2 fluxes in autumn, indicating that VOC release was driven by microbial activity.ConclusionsThis is the first study where below-ground VOC concentrations were quantified in situ, and for this reason, this study provides valuable insights to the VOC sources present in soils.

Highlights

Soil and understorey vegetation release volatile organic compounds (VOCs) from diverse storages and processes, including understorey vegetation, roots, decomposition processes, soil microbes, and vegetative litter concentrated in the O-horizon (Hayward et al 2001; Smolander et al 2006; Leff and Fierer 2008; Bäck et al 2010; Aaltonen et al 2011; Faubert et al 2012; Mäki et al 2017)
Belowground monoterpene concentrations were largely decoupled from forest floor monoterpene fluxes; it seems that production processes and storages of VOCs partly differ from those VOCs that are simultaneously released from the forest floor. Both fluxes and concentrations of the monoterpenes and sesquiterpenes correlated with the CO2 fluxes in autumn, indicating that VOC release was driven by microbial activity. This is the first study where below-ground VOC concentrations were quantified in situ, and for this reason, this study provides valuable insights to the VOC sources present in soils
Monoterpene concentrations and fluxes from the O-horizon are probably driven by the monoterpene-rich litter, in which the decomposition processes are regulated by litter quantity and quality, climate and soil microbial populations (Prescott et al 2000)

Summary

Introduction

Soil and understorey vegetation release volatile organic compounds (VOCs) from diverse storages and processes, including understorey vegetation, roots, decomposition processes, soil microbes, and vegetative litter concentrated in the O-horizon (Hayward et al 2001; Smolander et al 2006; Leff and Fierer 2008; Bäck et al 2010; Aaltonen et al 2011; Faubert et al 2012; Mäki et al 2017). CO2 uptake and respiration of ground vegetation is low in autumn (Kolari et al 2009). For this reason, CO2 fluxes from soils may be used to monitor microbial activity in autumn

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