BVOC fluxes in boreal forest floor and associated soil microbiome after forest fire

Boreal forests play a crucial role in emitting biogenic volatile organic compounds (BVOCs), which have both warming and cooling effects on the Earth's climate. These forests are among the primary sources of secondary organic aerosols (SOAs). Plant-emitted BVOCs, such as isoprenoids (including isoprene, monoterpenes, and sesquiterpenes), serve as precursors to SOAs, significantly affecting air quality and climate. Recent research indicates that forest fires also have long-term impacts on BVOC emissions, which are influenced by the frequency and severity of these fires, exacerbated by climate warming. Despite their importance, the effects of forest fires on BVOC emissions, their production and consumption by plants and associated soil microbes, as well as the underlying genetic mechanisms, remain poorly understood.

In this study, we quantify post-fire BVOC emissions from the forest floor, including above-ground plantlets, below-ground plant parts, and soil microbes by trapping forest floor BVOCs using a dynamic headspace technique. To investigate belowground BVOCs, we established mesocosms—blocks of soil with intact vegetation on top—within strictly controlled climate chambers. BVOCs were collected from mesocosm soil, as well as from root-free soil, using a dynamic enclosure technique. Soil DNA was extracted for amplification of 16S rRNA and ITS region from the samples and sent for sequencing to detect changes in microbial composition between pre- and post-fire conditions. We designed BVOC-specific probes for targeted metagenomics, such as those for monoterpene synthesis, isoprene synthesis, and monoterpene degrading enzymes, to analyze the production and consumption of BVOCs by the soil microbiome and to correlate these findings with forest floor BVOC flux data.

We have identified various volatile chemical groups, such as monoterpenes and isoprene, and quantified their fluxes in forest floor vegetation before and after fires. This study provides a clearer understanding of BVOC emissions and their consumption in the atmosphere from the boreal forest floor and soil microbiome under pre- and post-fire conditions.