Soil biochar amendment affects the diversity of nosZ transcripts: Implications for NO formation.

Microbial nitrogen transformation processes such as denitrification represent major sources of the potent greenhouse gas nitrous oxide (NO). Soil biochar amendment has been shown to significantly decrease NO emissions in various soils. However, the effect of biochar on the structure and function of microbial communities that actively perform nitrogen redox transformations has not been studied in detail yet. To analyse the community composition of actively denitrifying and NO-reducing microbial communities, we collected RNA samples at different time points from a soil microcosm experiment conducted under denitrifying conditions and performed Illumina amplicon sequencing targeting nirK, typical nosZ and atypical nosZ mRNA transcripts. Within 10 days, biochar significantly increased the diversity of nirK and typical nosZ transcripts and resulted in taxonomic shifts among the typical nosZ-expressing microbial community. Furthermore, biochar addition led to a significant increase in transcript production among microbial species that are specialized on direct NO reduction from the environment. Our results point towards a potential coupling of biochar-induced NO emission reduction and an increase in microbial NO reduction activity among specific groups of typical and atypical NO reducers. However, experiments with other soils and biochars will be required to verify the transferability of these findings to other soil-biochar systems.