Soil pH modulates the activity of low-affinity methane oxidation in soils from the Amazon region.

Aims: In the Amazon region, pastures are the main land use subsequent to deforestation and this change can result in soil acidification and degradation. Liming is a management practice to increase soil pH, important to recover degraded lands and increase soil fertility, but its impacts on soil methane cycling in tropical soils are unknown. Here we investigate the role of soil pH on methane uptake under high concentrations of the gas, manipulating pasture and forest soils pH by liming and evaluating the active methane cycling microbial community.

Methods And Results: Top layer of forest and pasture soils were subjected to liming treatment and incubated with ∼10 000 ppm of 13CH4. Soil DNA was evaluated with Stable Isotopic Probing (SIP-DNA), methanotrophic abundance was quantified (pmoA gene), and high throughput sequencing of 16S rRNA was performed. Liming increased the methane uptake in both forest (∼10%) and pasture (∼25%) soils. Methanotrophs Methylocaldum spp. (type I) and potential methanotrophs in Beijerinckiaceae (type II) were identified to actively incorporate carbon from methane in limed pasture soils. In limed forest soils, Nitrososphaeraceae were identified as 13C-enriched taxa, indicating that ammonia oxidizers can oxidize methane in these soils.

Conclusions: Liming Amazonian pasture soils not only contributes to the fertility and recovery of degraded areas but also has the potential to improve the oxidation of methane at high concentrations of this gas.