Nanna Schrøder Baggesen:
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Bidirectional exchange of biogenic volatile organic compounds (BVOCs) in the subarctic tundra is largely unexplored. Climate warming will be more pronounced in the arctic regions, which will also have an effect on BVOC exchange. In this thesis, I study different BVOCs in relation to climate change and plant developmental stages in both field and laboratory experiments. I look at the effects of temperature changes, leaf litter addition, and flooding, together with the indirect effects following these treatments. Furthermore, this thesis contains the first dataset showing the variations in BVOC exchange during both day and night.
We found clear patterns in BVOC exchange across day, night, and plant developmental stage, and we saw that different BVOCs behaved differently. Some compound groups showed both release and uptake, whereas other groups were almost exclusively released. In general, increasing temperatures resulted in higher release, because plant and soil microbial activity were also enhanced with warming. In contrast, flooding increased the uptake of BVOCs because soil microbes and plant roots were drowned and thus, their productivity was inhibited. Leaf litter adds nutrients and carbon to the ecosystem, which could increase the microbial activity and, like increasing temperatures, result in release of BVOCs. However, microbes can also use BVOCs as a carbon source and the net balance in the soil community is therefore dependent on microbial uptake and release. Consequently, the effects of lead litter addition varied between BVOCs. When looking at BVOC exchange over longer periods, we saw that the BVOC exchange followed the plant developmental stage and greenness of the vegetation to some degree.
Changes in temperature, leaf litter input, and flooding will eventually change which plant species that will survive in the ecosystem. We studied two different plant species, willow and birch, and saw that the individual species released different BVOCs. Different BVOCs have different effects in the atmosphere and therefore, it is important to know the BVOC compositions associated with the dominant plant species.