Ammonium sorption and ammonia inhibition of nitrite-oxidizing bacteria explain contrasting soil N2O production.

Rodney T. Venterea,Ping Wang,Florence Breuillin-Sessoms,Michael J. Sadowsky,Jeffrey A. Coulter,Timothy J. Clough

doi:10.1038/srep12153

Rodney T. Venterea, Ping Wang + Show 4 more

Open Access

https://doi.org/10.1038/srep12153

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Abstract

Better understanding of process controls over nitrous oxide (N2O) production in urine-impacted ‘hot spots’ and fertilizer bands is needed to improve mitigation strategies and emission models. Following amendment with bovine (Bos taurus) urine (Bu) or urea (Ur), we measured inorganic N, pH, N2O, and genes associated with nitrification in two soils (‘L’ and ‘W’) having similar texture, pH, C, and C/N ratio. Solution-phase ammonia (slNH3) was also calculated accounting for non-linear ammonium (NH4+) sorption capacities (ASC). Soil W displayed greater nitrification rates and nitrate (NO3−) levels than soil L, but was more resistant to nitrite (NO2−) accumulation and produced two to ten times less N2O than soil L. Genes associated with NO2− oxidation (nxrA) increased substantially in soil W but remained static in soil L. Soil NO2− was strongly correlated with N2O production, and cumulative (c-) slNH3 explained 87% of the variance in c-NO2−. Differences between soils were explained by greater slNH3 in soil L which inhibited NO2− oxidization leading to greater NO2− levels and N2O production. This is the first study to correlate the dynamics of soil slNH3, NO2−, N2O and nitrifier genes, and the first to show how ASC can regulate NO2− levels and N2O production.

Highlights

The presence of sufficiently high NH3 levels because NOB are unable to fully process the NO2− produced by AOB
Multiple regression models with c-slNH4+ and c-H+ as independent variables explained 93 and 89% of the variance in c-NO2− and c-actual N2O production rate (aN2O), respectively (Figs 5c,d). This is the first study to correlate the dynamics of slNH3, NO2−, N2O and nitrifier genes in incubating soil
The strong relationship (r2 = 0.87) between c-slNH3 and c-NO2− suggests that NH3 toxicity acting more strongly on NOB than AOB, and more strongly in soil L than in soil W, was responsible for the contrasting NO2− and N2O dynamics in the two soils[11,12,13,14]

Summary

Introduction

The presence of sufficiently high NH3 levels because NOB are unable to fully process the NO2− produced by AOB. Simultaneous quantification of genes associated with activities of NOB, AOB and NH4+ oxidizing archaea in soil following amendment with N has been reported in a few studies[16,17,18], but more data are needed to understand the role of nitrifier responses in regulating NO2− and N2O dynamics. Limited understanding of these and other factors limits our ability to predict NO2− dynamics for a particular soil, management practice, or climate condition, and our ability to predict N2O emissions resulting from NO2− transformations[19,20]. We conducted a series of experiments designed to elucidate controls over NO2− and N2O production under conditions representative of concentrated BU patches or Ur bands, and to explain the differences in N2O production between these soils

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Results

Conclusion