Stand type affects fluxes of volatile organic compounds from the forest floor in hemiboreal and boreal climates

Abstract

Aims The forest floor is a significant contributor to the stand-scale fluxes of biogenic volatile organic compounds. In this study, the effect of tree species (Scots pine vs. Norway spruce) on forest floor fluxes of volatile organic compounds (VOC) was compared in boreal and hemiboreal climates. Methods Monoterpenoid and sesquiterpene flux rates were determined during 2017-2018 using dynamic (steady-state flow-through) chambers placed on permanent soil collars on boreal and hemiboreal forest floors, where the canopy was formed by Scots pine (Pinus sylvestris), Norway spruce (Picea abies) or dominated by Scots pine with small coverage of Norway spruce and birches (Betula pendula and Betula pubescens). Results The total monoterpenoid fluxes were higher from the Scots pine forest floor (boreal 23 μg m −2 h −1 ) and from the mixed forest floor (hemiboreal 32 μg m −2 h −1 ) compared to the Norway spruce forest floor in both boreal (12 μg m −2 h −1 ) and hemiboreal (9 μg m −2 h −1 ) climates. Due to higher litterfall production, the forest floor seems to be a greater source of monoterpenoids and sesquiterpenes in the hemiboreal mixed stand dominated by Scots pine compared to the boreal Scots pine stand, although the difference was not statistically significant. Forest floor VOC fluxes followed a similar seasonal dynamic in different forest stands, with the highest flux rates in spring and summer. Significant VOC sources in the boreal forest floor were synthesis and release from vegetation and living roots together with litter decomposition of fungi and other microbes, where VOCs are released from needle storage pools. Ground vegetation in the hemiboreal forest is scanty under the dense tree canopy, meaning soil processes, such as litter decomposition, microbial metabolism and root release, were likely the dominating VOC sources. VOC fluxes from the hemiboreal forest floor were reduced by increases in soil moisture.Conclusions This study indicates that if the warming climate changes tree species' abundance and stand biomass, by increasing tree growth and coverage of broadleaf species, it may affect VOC fluxes from the forest floor and impact the total VOC emissions from northern soils.

Emissions of monoterpenes from new Scots pine foliage: dependency on season, stand age and location and importance for models

“…Scots pine (and ~25% other tree species), thus our results cannot be directly compared to Taipale et al (2011) and Rantala et al (2015), but these two studies provide the most suitable observations for validation of our results. We refer to Table A2 The reported canopy scale emission potentials agree very well with our suggested whole tree foliage emission potentials and the agreement is much better than that between Taipale et al 2011 Norway spruce (15 % of the stand) and deciduous species (~10 %) (Bäck et al, 2010;Aaltonen et al, 2011Aaltonen et al, , 2012Vanhatalo et al, 2015;Mäki et al, 2019).…”

“…In both studies, the micrometeorological measurements were conducted on the same ~50 year old Scots pine forest at the SMEAR II station (Station for Measuring Ecosystem-Atmosphere Relations). The canopy, within an area with a radius of 200 m, is made up by Scots pine (~75 %), Norway spruce (~15 %) and deciduous species (~10 %), mainly silver birch (Mäki et al, 2019). The potential of the forest to emit monoterpenes per ground area was in both cases shown to significantly decrease from spring and over the summer (Taipale et al, 2011;Rantala et al, 2015).…”

Overview: Recent advances on the understanding of the Northern Eurasian environments and of the urban air quality in China - Pan Eurasian Experiment (PEEX) program perspective

“…The abundance of tree species, stand biomass, increasing tree growth and coverage of broadleaf species may also affect biogenic volatile organic compound (BVOC) emissions from the forest floor and impact the total BVOC emissions from northern soils. At least the stand type has been shown to affect BVOCs fluxes from the forest floor in a hemi boreal -boreal region (Mäki et al, 2019). As a whole, BVOCs emitted by boreal evergreen trees are connected to the photosynthetic activity with a strong seasonality and have a crucial role to atmospheric aerosol formation processes over the boreal forest zone.…”

Emission of volatile organic compounds by plants on the floor of boreal and mid-latitude forests

“…In recent years, much attention has been paid to decaying deciduous litter as a source of atmospheric VOCs (Isidorov et al 1999;Isidorov and Janova 2002;Isidorov et al , 2005Isidorov et al , 2010Hellén et al 2006;Gray et al 2010;Aaltonen et al 2011Aaltonen et al , 2013Geenberg et al 2012;Mäki et al 2019aMäki et al , 2019bViros et al 2020Viros et al , 2021. Quantification of VOC emissions from the forest floor is mainly carried out using flow chambers installed on the soil (Janson 1993;Isidorov et al 1994;Hayward et al 2001;Hellén et al 2006;Asensio et al 2007;Greenberg et al 2012;Mäki et al 2017Mäki et al , 2019aKivimäenpää et al 2018;Wang et al 2018), but this technique allows the determination of gross fluxes without differentiation into individual elements such as deciduous litter, live plants, soil and root exudates from trees.…”