Discrepancy in exchangeable and soluble ammonium-induced effects on aerobic methane oxidation

a microcosm study of a paddy soil

authored by
Hester van Dijk, Thomas Kaupper, Clemens Bothe, Hyo Jung Lee, Paul L. E. Bodelier, Marcus A. Horn, Adrian Ho

Ammonium-induced stimulatory, inhibitory, and/or neutral effects on soil methane oxidation have been attributable to the ammonium concentration and mineral forms, confounded by other edaphic properties (e.g., pH, salinity), as well as the site-specific composition of the methanotrophic community. We hypothesize that this inconsistency may stem from the discrepancy in the cation adsorption capacity of the soil. We postulate that the effects of ammonium on the methanotrophic activity in soil are more accurately portrayed by relating methane uptake rates to the soluble ammonium (bioavailable), rather than the exchangeable (total) ammonium. To reduce adsorption (exchangeable) sites for ammonium in a paddy soil, two successive pre-incubation steps were introduced resulting in a 1000-fold soil dilution (soil enrichment), to be compared to a soil slurry (tenfold dilution) incubation. Ammonium was supplemented as NH

4Cl at 0.5–4.75gL

−1 after pre-incubation. While NH

4Cl significantly stimulated the methanotrophic activity at all concentrations in the soil slurry incubation, methane uptake showed a dose-dependent effect in the soil enrichment. The trend in methane uptake could be explained by the soluble ammonium concentration, which was proportionate to the supplemented ammonium in the soil enrichment. In the soil slurry incubation, a fraction (36–63%) of the supplemented ammonium was determined to be adsorbed to the soil. Accordingly, Methylosarcina was found to predominate the methanotrophic community after the incubation, suggesting the relevance of this methanotroph at elevated ammonium levels (< 3.25gL

−1 NH

4Cl). Collectively, our results showed that the soluble, rather than the exchangeable ammonium concentration, is relevant when determining the effects of ammonium on methane oxidation, but this does not exclude other (a)biotic factors concurrently influencing methanotrophic activity.

Institute of Microbiology
External Organisation(s)
Kunsan National University
Netherlands Institute of Ecology
Biology and fertility of soils
No. of pages
Publication date
Publication status
Peer reviewed
ASJC Scopus subject areas
Agronomy and Crop Science, Soil Science, Microbiology
Electronic version(s)
https://doi.org/10.1007/s00374-021-01579-9 (Access: Open)