The conversion of primary rainforest (PF) (i.e., mature rainforest older than 150 years) to cattle pasture is a main cause of deforestation in Brazil and not only changes plant diversity but also the microorganisms that drive soil biogeochemical cycling.

In the Amazon rainforest particularly, over 1 Mha of forest has been lost in 2017 alone. However, rainforest deforestation to create cattle pastures or agricultural fields releases large amounts of stored carbon, converting former terrestrial carbon sinks into major carbon sources. In addition to being biodiversity hotspots of plants and animals, tropical rainforests are large terrestrial carbon sinks. Specifically, tropical deforestation in the last decade has released ~1 Pg C yr −1, an equivalent to 10% of anthropogenic carbon dioxide emissions, and 78% of total greenhouse gas emissions in Brazil are caused by land use change. Although the majority of greenhouse gases released to the atmosphere are associated with the industrial revolution and fossil fuel combustion, land-use change is a significant contributor. These findings are critical for informing land management practices and global tropical rainforest conservation.Ĭlimate change, caused by the anthropogenic release of greenhouse gases, is affecting every ecosystem on Earth.

Furthermore, we found that secondary rainforests had decreased methanogenic activity similar to primary rainforests, and thus a potential to recover as methane sinks, making it conceivable for forest restoration to offset greenhouse gas emissions in the tropics. We conclude that a significant increase in the abundance and activity of methanogens in pasture soils could drive increased soil methane emissions. At both locations, we observed a significant change in the composition of the isotope-labeled methane-cycling microbial community across land use types, specifically an increase in the abundance and diversity of active methanogens in pastures. We collected intact soil cores from three land use types (primary rainforest, pasture, and secondary rainforest) of two geographically distinct areas of the Brazilian Amazon (Santarém, Pará and Ariquemes, Rondônia) and performed DNA stable-isotope probing coupled with metagenomics to identify the active methanotrophs and methanogens. The biotic methane cycle is driven by microorganisms therefore, this study focused on active methane-cycling microorganisms and their functions across land-use types. Rainforest-to-pasture conversion stimulates the release of methane, a potent greenhouse gas. The Amazon rainforest is a biodiversity hotspot and large terrestrial carbon sink threatened by agricultural conversion.

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