Differences in the uptake of biogenic volatile organic compounds (BVOCs) between habitat types and peat layers in boreal peatlands

Biogenic volatile organic compounds (BVOCs) released by boreal vegetation have a net cooling impact on climate, both in the boreal and Arctic regions. While boreal forests play a major role in this process, the release and uptake of BVOCs in peatlands is poorly understood, even though they cover up to 28% of the boreal region. Furthermore, soil BVOC sinks and sources are an understudied component of the boreal BVOC budget. Recently, microbial uptake of BVOCs has been found to regulate BVOC release from the soil into the atmosphere. In peatlands, methane emissions from the peat are known to be controlled by microbial oxidation within the living mosses, but it is unknown whether similar uptake occurs with BVOCs. Our aim was to quantify the release and uptake of BVOCs across different boreal peatland habitats. We collected peat samples, including the living moss layer, from four peatland habitats varying in fertility, wetness, and vegetation composition (bog hollow, bog hummock, fen, bog peat). The samples were split into the living moss layer, as well as the oxic and anoxic peat layers, above and below the water table, respectively. First, we investigated the potential uptake of peat-derived BVOCs in the living moss layer by incubating the peat and moss layers in glass jars both separately and together with other layers from the same habitat. Next, we quantified the uptake of four specific compounds by introducing 13C-labeled BVOCs into jars containing peat or moss layers. The magnitude and compound composition of BVOCs was measured with proton transfer reaction–time of flight–mass spectrometry (PTR-TOF-MS). Contrary to our expectations, BVOC uptake of peat-derived compounds was observed in the living moss layer, as well as in the oxic and anoxic peat layers. The most important layer for BVOC release and uptake varied between the peatland habitats. For example, the number of released compounds and the total BVOC emissions were largest for anoxic peat in the fen, while it was the living mosses in the bog hollow. Anoxic bog peat had the largest BVOC uptake of all of the habitats and layers. BVOC uptake varied between the studied compounds; while ethanol was taken up by all layers in every habitat, we observed no uptake of acetic acid. Acetone was mostly consumed in the peat layers, while acetaldehyde uptake occurred in bog hummock and fen habitats, regardless of the layer. According to our results, BVOC emissions from boreal peatland soil into the atmosphere are a net outcome of production and consumption both in the peat and moss layers. As these patterns vary even within habitats of the same site, changes in vegetation have the potential to modify BVOC fluxes in boreal peatlands.