Abstract. Denitriﬁcation is an anaerobic respiration process that is the primary contributor of the nitrous oxide (N O) produced from grassland soils. Our objective was to gain insight into the relationships between denitriﬁer community size, structure, and activity for a range of pasture soils. We collected 10 dairy pasture soils with contrasting soil textures, drainage classes, management strategies (efﬂuent irrigation or non-irrigation), and geographic locations in New Zealand, and measured their physicochemical characteristics. We measured denitriﬁer abundance by quantitative polymerase chain reaction (qPCR) and assessed denitriﬁer diversity and community structure by terminal restriction fragment length polymorphism (T-RFLP) of the nitrite reductase (nirS, nirK) and N O reductase (nosZ) genes. We quantiﬁed denitriﬁer enzyme activity (DEA) using an acetylene inhibition technique. We investigated whether varied soil conditions lead to different denitriﬁer communities in soils, and if so, whether they are associated with different denitriﬁcation activities and are likely to generate different N 2 O emissions. Differences in the physicochemical characteristics of the soils were driven mainly by soil mineralogy and the management practices of the farms. We found that nirS and nirK communities were strongly structured along gradients of soil water and phosphorus (P) contents. By contrast, the size and structure of the nosZ community was unrelated to any of the measured soil characteristics. In soils with high water content, the richnesses and abundances of nirS, nirK, and nosZ genes were all signiﬁcantly positively correlated with DEA. Our data suggest that management strategies to limit N O emissions through denitriﬁcation are likely to be most im- 2 2 2 portant for dairy farms on fertile or allophanic soils during wetter periods. Finally, our data suggest that new techniques that would selectively target nirS denitriﬁers may be the most effective for limiting N O emissions through denitriﬁcation across a wide range of soil types.
Biogeosciences, 2017, 2017, 14 (N/A), pp. 4243 - 4253 (10)