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

Abstract

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.

Organisation(s)

Institute of Microbiology

External Organisation(s)

Kunsan National University
Netherlands Institute of Ecology

Type

Article

Journal

Biology and fertility of soils

Volume

Pages

873-880

No. of pages

ISSN

0178-2762

Publication date

08.2021

Publication status

Published

Peer reviewed

Yes

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)