1. Impact of nitrogen compounds on fungal and bacterial contributions to codenitrification in a pasture soil.
- Author
-
Rex D, Clough TJ, Richards KG, Condron LM, de Klein CAM, Morales SE, and Lanigan GJ
- Subjects
- Agriculture, Bacteria metabolism, Fungi metabolism, Grassland, Nitrogen Compounds metabolism, Nitrous Oxide metabolism, Soil chemistry, Denitrification physiology, Nitrogen metabolism, Soil Microbiology
- Abstract
Ruminant urine patches on grazed grassland are a significant source of agricultural nitrous oxide (N
2 O) emissions. Of the many biotic and abiotic N2 O production mechanisms initiated following urine-urea deposition, codenitrification resulting in the formation of hybrid N2 O, is one of the least understood. Codenitrification forms hybrid N2 O via biotic N-nitrosation, co-metabolising organic and inorganic N compounds (N substrates) to produce N2 O. The objective of this study was to assess the relative significance of different N substrates on codenitrification and to determine the contributions of fungi and bacteria to codenitrification.15 N-labelled ammonium, hydroxylamine (NH2 OH) and two amino acids (phenylalanine or glycine) were applied, separately, to sieved soil mesocosms eight days after a simulated urine event, in the absence or presence of bacterial and fungal inhibitors. Soil chemical variables and N2 O fluxes were monitored and the codenitrified N2 O fluxes determined. Fungal inhibition decreased N2 O fluxes by ca. 40% for both amino acid treatments, while bacterial inhibition only decreased the N2 O flux of the glycine treatment, by 14%. Hydroxylamine (NH2 OH) generated the highest N2 O fluxes which declined with either fungal or bacterial inhibition alone, while combined inhibition resulted in a 60% decrease in the N2 O flux. All the N substrates examined participated to some extent in codenitrification. Trends for codenitrification under the NH2 OH substrate treatment followed those of total N2 O fluxes (85.7% of total N2 O flux). Codenitrification fluxes under non-NH2 OH substrate treatments (0.7-1.2% of total N2 O flux) were two orders of magnitude lower, and significant decreases in these treatments only occurred with fungal inhibition in the amino acid substrate treatments. These results demonstrate that in situ studies are required to better understand the dynamics of codenitrification substrates in grazed pasture soils and the associated role that fungi have with respect to codenitrification.- Published
- 2019
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