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 NH₄Cl at 0.5–4.75gL⁻¹ after pre-incubation. While NH₄Cl 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 NH₄Cl). 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.

铵对土壤甲烷氧化的刺激、抑制和/或中性影响归因于铵浓度和矿物质形式，被其他土壤特性（例如 pH 值、盐度）以及特定地点的土壤成分混淆甲烷营养社区。我们假设这种不一致可能源于土壤阳离子吸附能力的差异。我们假设，通过将甲烷吸收率与可溶性铵（生物可利用性）而不是可交换（总）铵相关联，可以更准确地描述铵对土壤中甲烷氧化活性的影响。为了减少稻田中铵的吸附（可交换）位点，引入了两个连续的预孵化步骤，导致土壤稀释（土壤富集）1000 倍，与土壤浆液（十倍稀释）培养相比较。铵以NH形式补充预孵育后0.5–4.75gL ^{-1 的}₄ Cl 。虽然 NH ₄ Cl 显着刺激了土壤浆液培养中所有浓度的甲烷氧化活性，但甲烷吸收在土壤富集中表现出剂量依赖性效应。甲烷吸收的趋势可以用可溶性铵浓度来解释，这与土壤富集中补充的铵成正比。在土壤泥浆培养中，一部分（36-63%）的补充铵被确定吸附到土壤上。因此，发现Methylosarcina在孵化后在甲烷氧化菌群落中占主导地位，这表明该甲烷氧化菌在铵水平升高（< 3.25gL ^-1 NH ₄CL）。总的来说，我们的结果表明，在确定铵对甲烷氧化的影响时，可溶铵浓度而不是可交换铵浓度是相关的，但这并不排除同时影响甲烷氧化活性的其他（a）生物因素。