Nitrous oxide (N 2 O) is a major long-lived greenhouse gas with rising atmospheric concentration. Denitrifiers are important sources and sinks of N 2 O in soils when oxygen becomes limited. Denitrification potentials highly depend on various environmental factors and microbial community traits might be key determinants controlling denitrification rates. However, robust links between microbial community structures and process potentials across systems are lacking. We hypothesize that contrasting edaphic factors shape dissimilar denitrifier communities in soil that have dissimilar kinetic traits, thus constraining the soil’s anaerobic denitrification and N 2 O consumption capacities. Consequently, we determined apparent Michaelis-Menten kinetics of nitrate and N 2 O consumption in anoxic microcosms of three contrasting soils. Apparent maximal reaction velocities for nitrate and N 2 O ranged from 40 to 340 and 20 to 540 nM min -1 , respectively. Nitrogen mass balances indicated a significant contribution of denitrification rather than dissimilatory nitrate reduction to ammonium (DNRA) to NO 3 - reduction. Quantitative PCR and amplicon sequencing of 16S rRNA and marker genes coding for enzymes involved in denitrification and DNRA demonstrated contrasting denitrifier and DNRA communities in the three soils. Bradyrhizobium sp. was the most discriminative denitrifying taxon, while Opitutaceae and Gemmatimonadaceae were decisive for N 2 O reducers. Estimated “cell”-specific maximal reaction velocities ranged from 1-10 and 5-90 fmol gene -1 h -1 for soil denitrifiers and N 2 O reducers, respectively. Abundances of genes encoding the cytochrome dependent nitrite reductase ( nirS ) and of those encoding N 2 O reductase ( nosZII ) correlated well with apparent maximal reaction velocities. Such data suggests that denitrification activity and N 2 O emissions are modulated within the boundary conditions defined by the capabilities of a given denitrifier community, which (i) has consequences for modelling of the N-cycle, (ii) can help to reveal important ecological drivers of microbial guilds and their activities, and provides a basis for developing management strategies tailored to the level of activity of the microbiome.
Dijk et al. (Fri,) studied this question.