Nitrite accumulation and impairment of N2O reduction explains contrasting soil denitrification phenotypes. (March 2022)

• Record Type: Journal Article
• Authors: Highton, Matthew P.; Bakken, Lars R.; Dörsch, Peter; Molstad, Lars; Morales, Sergio E.
• Is Part Of: Soil biology and biochemistry. Volume 166(2022)
• Publication Date: 2022-03
• Subjects: Denitrification -- Nitrite -- Inhibition -- N2O reduction; Soil biochemistry -- Periodicals; Soil biology -- Periodicals; Sols -- Biochimie -- Périodiques; Sols -- Biologie -- Périodiques; Sols -- Microbiologie -- Périodiques; Bodembiologie; Biochemie; 631.46
• DOI: 10.1016/j.soilbio.2021.108529
• Languages: English
• ISSNs: 0038-0717

Abstract

Abstract: Soil denitrification produces the potent greenhouse gas and ozone depleter nitrous oxide (N2 O). We previously linked soil N2 O emission potential (N2 O/N2 O + N2 ) to a continuum of denitrification phenotypes in 20 pasture soils but were unable to determine their proximal cause. At one end of the continuum, soils carried out completely concurrent production and reduction of N2 O (concurrent phenotype) while at the other end soils delayed N2 O reduction until almost all added nitrate (NO3 − ) was accumulated as N2 O (sequential phenotype). In an unsealed environment, the later phenotype is predicted to emit most added N as N2 O. Here we tested the role of delayed N2 O reductase synthesis and nitrite (NO2 − ) based impairment of N2 O reduction as determinants of delayed N2 O reduction in soils with sequential phenotypes. Nitric oxide (NO), N2 O and N2 accumulation were measured in response to added NO3 −, NO2 − and N2 O in anoxic batch incubations of fresh or pre-incubated soil using automated gas chromatography. Successive NO3 − additions drove 6 of 7 soils towards increasingly concurrent N2 O production/reduction, suggesting delayed production of N2 O reductase may be the cause of delayed N2 O reduction in initially sequentially denitrifying soils. NO2 − addition (2 mM NO3 − + 1 mM NO2 − vs. 3 mM NO3 − control) to sequentially and concurrently denitrifying soil demonstrated that NO2 − impairs N2 O reduction, even when N2 O reductase was fully induced (pre-incubated soils, 1 mM NO2 − + 42 μmol N2 O vs. 42 μmol N2 O control). Further, 2 pieces of evidence suggest that differences in NO2 − accumulation are a probable cause of the previously observed denitrification phenotypes. 1) 48 fold higher NO2 − accumulation in the sequential vs. concurrent soil in response to 3 mM NO3 − addition. 2) the concurrent timing of NO2 − depletion/N2 O reduction in the sequential soil. However, these observations should be confirmed in a greater number of soils. Inhibition of N2 O reductase by NO is proposed as a potential proximal cause of impaired early N2 O reduction which could link separate effectors (NO2 −, carbon, successive NO3 − additions) to a common inhibitory mechanism. Highlights: A soil with delayed N2 O reduction accumulated high levels of nitrite. Nitrite addition impaired N2 O reduction regardless of the soils original status. Soils with pre-synthesised N2 O reductase were still susceptible to nitrite inhibition. NO accumulation may be linked to impairment of N2 O reduction.