Contribution of understorey vegetation and soil processes to boreal forest isoprenoid exchange

Mari Mäki, Jussi Heinonsalo, Heidi Hellén, Jaana Bäck
2016 Biogeosciences Discussions  
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. Our study takes one step forward, with the aim of separately determining whether the photosynthesized carbon allocation to soil affects the isoprenoid production by different soil organisms, i.e.
more » ... l 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&amp;thinsp;μm mesh size) or the ingrowth of roots and fungi (1μm mesh) into the soil volume, which is called the trenching approach. We measured isoprenoid fluxes using dynamic (steady-state flow-through) chambers from the different treatments. We also aimed to analyze how important the understorey vegetation is as a VOC sink. Finally, we constructed a statistical model 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. Our 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&amp;thinsp;μg&amp;thinsp;m<sup>&amp;minus;2</sup>&amp;thinsp;h<sup>&amp;minus;1</sup>. Our results 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. We also discovered that understorey vegetation is a strong sink of monoterpenes. Our statistical model, based on prevailing temperature, seasonality, vegetation effect, and the interaction of these parameters, explained 43% of the monoterpene fluxes, and 34&amp;ndash;46&amp;thinsp;% of individual α-pinene, camphene, β-pinene and Δ<sup>3</sup>-carene fluxes.
doi:10.5194/bg-2016-255 fatcat:u452g4mkqraabc7czfncrsphfe