Magnus Kramshøj:
Biogenic volatile organic compounds in a changing climate

Date: 30-01-2018    Supervisor: Riika Rinnan



All living organisms release non-methane biogenic volatile organic compounds (BVOCs), which are reactive gases that have both negative and positive climate forcing impacts. The atmospheric oxidation of these gases, contribute to particle growth potentially facilitating cloud formation, and affect the lifetime of the greenhouse gases methane and ozone. The Arctic is particularly sensitive to climate changes and is currently experiencing climate warming at twice the rate compared to the global mean. BVOC emission has previously been considered insignificant in the Arctic, however due to an extreme sensitivity of BVOCs to climate changes their importance in the region might increase. Arctic temperature and cloud cover is projected to increase in the future, and this could affect the release of BVOCs since emission from vegetation is dependent on temperature and light availability. Northern Hemisphere permafrost soils, that store more than 1500 Pg of organic carbon, are thawing due to climate warming. These soils release greenhouse gases, but if they also release BVOCs has so far not been studied. Soil BVOC fluxes are in general understudied even though they can take up BVOCs, which is a process only poorly understood. I use the enclosure technique and collect volatiles in adsorbent cartridges, later analysed by gas chromatography – mass spectrometry, in combination with direct measurements using Proton Transfer Reaction – Time of Flight – Mass Spectrometry. In this thesis I find that warming by 2-3 °C causes BVOC emissions from an Arctic heath to increase by 260%, while reduced sunlight causes emissions to decrease by 70%. The emission response to warming was driven by plants rather than soil, and warming increased emissions directly as opposed to via a growth in plant biomass. Furthermore, I show for the first time that thawing permafrost soils release a wide range of BVOCs. The majority of this release was however taken up by the active layer above the permafrost soil. The uptake was the result of a fast microbial BVOC degradation in the soil, that varied between specific compounds and ecosystem types. Melt water drainage of thawing permafrost soils influenced both the abundance and composition of BVOCs released, possibly due to altered microbial degradation and dissolution in the water. My results emphasize the high temperature and light sensitivity of Arctic plant BVOC emissions in response to climate changes, and the emission potential of thawing permafrost soil together with the importance of microbial uptake.