Mineralizable nitrogen and denitrification enzyme activity drive nitrate concentrations in well-drained stony subsoil under lucerne (Medicago sativa L.)

Nitrogen (N) inputs to agricultural systems contribute substantially soil nitrate (NO3−) concentrations, which increase NO3− leaching and contamination of groundwater. The influence microbes in regulating concentrations the topsoil are well studied but it is often assumed that microbial regulation subsoil negligible. aim this study was test assumption by determining relationships between properties both topsoil. We measured size mineralizable N (Nm) pool, (microbial biomass, bacterial richness), nitrifier gene abundance (amoA copy number), denitrifier (nirK nirS enzyme activity a well-drained stony under an established lucerne crop. used structural equation modelling (SEM) identify compare linkages with at each depth. In topsoil, we found higher Nm, abundance, denitrification activity, richness, biomass than those subsoil, there were no these variables (the SEM model explained 0.06% variability concentrations). contrast, strongly correlated amoA associated significantly Nm. richness also Nm subsoil. Our findings highlight 82% concentrations) suggest nitrification may contributes reducing conclude studies addressing drivers need consider potential for microbially-mediated attenuation (or increase) throughout profile.