nosZII communities influence soil N2O consumption potential in a long-term tillage and fertilization experiment

Emissions of N 2 O have an important environmental impact, with fertilization in agricultural systems contributing a substantial part. Understanding how different agricultural practices influence microbial processes governing N 2 O production and consumption is therefore urgently needed. This study aims to elucidate the underlying mechanisms driving N 2 O emissions in experimental plots subject to a combination of different tillage and fertilization practices. N 2 O consumption potential was evaluated in soil sampled from the field experiment by determining the genetic potential for N 2 O consumption/production and by measuring potential N 2 O production and denitrification activity (PDA) assays with and without carbon (C) substrate. The highest N 2 O consumption potential was observed in soil from organically fertilized no-till treatment. Addition of C to the PDA assay significantly increased N 2 O consumption in conventionally tilled soil, which exhibited higher proportion of nosZ II genes, coding for clade II nitrous oxide reductase, in the metagenome, and a more diverse microbial community. Correspondingly, the proportion and abundance of nosZ II genes as well as microbial diversity were significantly and positively related to N 2 O consumption potential. Gradients in soil physical and chemical properties reflected the tillage-driven differences in the composition of microbial communities, which however did not correlate with N 2 O consumption potential. Our findings suggest that overall taxonomy-based community structure had less importance for N 2 O consumption potential. Instead, the negative correlation between nosZ II gene and the N 2 O/(N 2 O + N 2 ) ratio emphasises the need to examine microbial functional capacity for better prediction of process outcomes.