Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 14, 1055-1073, 2017
http://www.biogeosciences.net/14/1055/2017/
doi:10.5194/bg-14-1055-2017
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
08 Mar 2017
Contribution of understorey vegetation and soil processes to boreal forest isoprenoid exchange
Mari Mäki1, Jussi Heinonsalo2, Heidi Hellén3, and Jaana Bäck1 1Department of Forest Sciences, P.O. Box 27, 00014 University of Helsinki, Helsinki, Finland
2Department of Food and Environmental Sciences, P.O. Box 66, 00014 University of Helsinki, Helsinki, Finland
3Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, Finland
Abstract. Boreal forest floor emits biogenic volatile organic compounds (BVOCs) from the understorey vegetation and the heterogeneous soil matrix, where the interactions of soil organisms and soil chemistry are complex. Earlier studies have focused on determining the net exchange of VOCs from the forest floor. This study goes one step further, with the aim of separately determining whether the photosynthesized carbon allocation to soil affects the isoprenoid production by different soil organisms, i.e., decomposers, mycorrhizal fungi, and roots. In each treatment, photosynthesized carbon allocation through roots for decomposers and mycorrhizal fungi was controlled by either preventing root ingrowth (50 µm mesh size) or the ingrowth of roots and fungi (1 µm mesh) into the soil volume, which is called the trenching approach. Isoprenoid fluxes were measured using dynamic (steady-state flow-through) chambers from the different treatments. This study aimed to analyze how important the understorey vegetation is as a VOC sink. Finally, a statistical model was constructed based on prevailing temperature, seasonality, trenching treatments, understory vegetation cover, above canopy photosynthetically active radiation (PAR), soil water content, and soil temperature to estimate isoprenoid fluxes. The final model included parameters with a statistically significant effect on the isoprenoid fluxes. The results show that the boreal forest floor emits monoterpenes, sesquiterpenes, and isoprene. Monoterpenes were the most common group of emitted isoprenoids, and the average flux from the non-trenched forest floor was 23 µg m−2 h−1. The results also show that different biological factors, including litterfall, carbon availability, biological activity in the soil, and physico-chemical processes, such as volatilization and absorption to the surfaces, are important at various times of the year. This study also discovered that understorey vegetation is a strong sink of monoterpenes. The statistical model, based on prevailing temperature, seasonality, vegetation effect, and the interaction of these parameters, explained 43 % of the monoterpene fluxes, and 34–46 % of individual α-pinene, camphene, β-pinene, and Δ3-carene fluxes.

Citation: Mäki, M., Heinonsalo, J., Hellén, H., and Bäck, J.: Contribution of understorey vegetation and soil processes to boreal forest isoprenoid exchange, Biogeosciences, 14, 1055-1073, doi:10.5194/bg-14-1055-2017, 2017.
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Short summary
The paper demonstrates which different biological factors and physico-chemical processes are important regulators of soil isoprenoid emissions at different times of the year. With the obtained knowledge on soil VOC sources, it will be possible to add soil VOC production into air chemistry models and thus improve the understanding on climatic feedback mechanisms between secondary organic aerosol formation, clouds, and radiative forcing.
The paper demonstrates which different biological factors and physico-chemical processes are...
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