Climate change may alter methane emissions and absorption in the Amazon

Extreme temperatures and humidity levels (excessive rain or drought) projected for the Amazon under climate change could increase the volume of methane-producing microorganisms in flooded areas and reduce potential uptake by 70% of this greenhouse gas in high altitude forests, with a global impact. impacts, according to a study led by researchers from the University of São Paulo (USP) in Brazil.

An article reporting their findings is published in the journal Environmental microbiome. Effective conservation and management policies are even more important in light of the findings, the researchers said.

For at least six months each year, more than 800,000 square kilometers of floodplains in the Amazon rainforest, equivalent to 20% of its total area, remain under several meters of water due to constant precipitation and rising levels of rivers in the region. Methane production increases as microbial communities break down organic matter.

Recent studies show that Amazon floodplains contribute 29% of global methane emissions from wetlands. On the other hand, the region’s high-altitude forests act as methane sinks, capturing gases from the atmosphere and playing an important role in regulating greenhouse gas emissions.

“While it has already been shown that factors such as air temperature and seasonal flooding can influence the composition of microbial communities and therefore affect methane flux in these environments, what should we expect in the context of climate change and projected changes in precipitation and temperature extremes, with more intense extremes,” said Júlia Brandão Gontijo, first author of the paper and currently a postdoctoral researcher at the University of California, Davis.

The study was part of Gontijo’s Ph.D. research at the Center for Nuclear Energy in Agriculture (CENA-USP), with Professor Tsai Siu Mui as thesis supervisor. “We know that atmospheric methane levels have increased by about 18% over the past four decades,” Tsai said.

In partnership with colleagues affiliated with the Netherlands Institute of Ecology of the Royal Netherlands Academy of Arts and Sciences (NIOO-KNAW), Stanford University, the University of Massachusetts and the At the University of Oregon in the United States, as well as the Federal University of Western Pará (UFOPA) in Brazil, Gontijo conducted a 30-day experiment in which soil samples from two floodplains and of a high altitude forest in Santarém and Belterra, municipalities located in the west of the state of Pará, were subjected to extreme temperatures (27 °C and 30 °C) and humidity.

Methane producers and consumers were identified and measured by genetic sequencing and quantitative real-time PCR.

“In both floodplains, although we did not observe significant changes in methane emission patterns, the number of methane-producing microorganisms increased, which could portend a future problem,” he said. Gontijo said.

Furthermore, methane consumption by upland forest soils fell by 70% under hot, dry conditions, while methane production increased significantly during periods of heavy rain, precisely because the soil n has not been regularly exposed to extreme humidity. For Gontijo, this is alarming.

“This means that the floodplain microbiome can adapt to climate change, but the upland forest microbiome is sensitive to its effects, which could lead to a shift in the balance of gas emissions in the future “Given the importance of the Amazon rainforest biome in proportion to global levels, this could represent a very serious problem,” she said.

Methanotrophs

The microbiota and the methane cycle in the Amazon will clearly be affected by climate change. In addition to their projections of increased methane emissions, the researchers also identified large numbers of methanotrophic microorganisms that use methane as an energy source and could potentially offset this increase. They now plan to conduct field experiments and laboratory tests involving microorganisms to better understand the dynamics of the methane cycle.

“Regardless, the information we have collected so far is extremely important and can be used in formulating public policies,” Gontijo said.