Tracking transcription in soil microbial communities during the Birch Effect

In drought affected ecosystems, a large portion of the annually respired CO₂ from soil may occur in the short period following the first rain event after drought. This process, where the rewetting of dry soil results in a pulse of CO­₂, is commonly known as the Birch Effect. This pulse of activity influences the stability and persistence of soil carbon which, considering the large and growing extent of dryland and drought-impacted ecosystems, may have far reaching implications. It’s been shown that the consumption of the compounds driving the Birch Effect varies temporally and that different taxa grow over the course of wet-up; however, the transcriptional response of specific taxa during wet-up, and their associated characteristics, has not been fully explored.  In this study we map metatranscriptomes against metagenome-assembled genomes (MAGs) in order to assess the transcriptional response of taxa to wet-up at 0, 3, 24, 48, 72, and 168 h post rewetting. We found distinct temporal response patterns that were often conserved on the family-level. Based on response patterns, we grouped genomes into early, mid, and late responders. The average transcriptional profile of MAGs within these different response types did not vary substantially from each other. Instead, for a majority of MAGs, we found shifts in the transcriptional profile of functional genes over time. Together, these findings suggest that much of the temporal dynamics of microbial transcription during the Birch Effect are controlled by differences in within-taxa response time as opposed to stark differences in functional gene transcription between response groups.