Climate change threatens to alter methane emissions in the Amazon, study reveals

Methane absorbtion could reduce by as much as 70% in warmer conditions
Climate change is potentially increasing emissions from flooded areas while reducing the Amazon’s capacity to absorb the gas in upland forests
Climate change is potentially increasing emissions from flooded areas while reducing the Amazon’s capacity to absorb the gas in upland forestsiStock
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Climate change could significantly disrupt emissions and uptake of greenhouse gases in the Amazon rainforest, with wide-reaching global consequences. Rising temperatures and increased flooding are affecting microbial activity in floodplain and upland forest soils, leading to contrasting changes in methane dynamics, warns new research from the University of São Paulo.

The study, recently published in the journal Environmental Microbiome, points to an alarming shift in methane uptake and emissions. Given the Amazon’s critical role in regulating global methane levels, these changes could contribute to worsening greenhouse gas concentrations worldwide.

Contrasting responses in floodplains and upland forests

Floodplains in the Amazon, which cover over 800,000 square kilometres during the rainy season, contribute up to 29 per cent of global wetland methane emissions. In these waterlogged areas, methane-producing microbes thrive as they break down organic matter. However, new findings indicate that upland forests, which typically act as methane sinks, are highly vulnerable to changes in temperature and humidity levels.

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Climate change is potentially increasing emissions from flooded areas while reducing the Amazon’s capacity to absorb the gas in upland forests

Lead author Júlia Brandão Gontijo, currently a postdoctoral researcher at the University of California, Davis in the United States, and her colleagues subjected soil samples from both ecosystems to extreme conditions — temperatures of 27°C and 30°C and varying humidity levels — during a 30-day experiment. Their research demonstrated that while methane emissions in floodplains remained stable, the number of methane-producing microbes increased. 

In contrast, methane uptake in upland forest soils plummeted by 70 per cent in dry, warm conditions, pointing to the greater sensitivity of upland soil microbes to temperature fluctuations. Higher temperatures reduced the overall number of bacteria and archaea in upland forests, while increasing the proportion of specialist microbes, the study also revealed, highlighting the fragility of these ecosystems in the face of climate change.

The paper was supported by public institution São Paulo Research Foundation (FAPESP). 

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Climate change is potentially increasing emissions from flooded areas while reducing the Amazon’s capacity to absorb the gas in upland forests

Methane cycling in the Amazon

The research also delved into the role of methanotrophic microorganisms, which consume methane. Isotope analysis revealed that both aerobic and anaerobic methane-consuming microbes were active in floodplains, underscoring the complex interactions that govern methane cycling in the Amazon. 

“It means that the floodplain microbiome can adapt to climate change but the upland forest microbiome is sensitive to its effects, which could cause an alteration in the balance of greenhouse gas emissions in the Amazon region in future. In view of the Amazon Rainforest biome’s importance in proportion to global levels, this could represent a very serious problem,” Gontijo told news agency Agência FAPESP.

This difference in microbial activity between floodplains and upland forests highlights the need for a nuanced understanding of how climate, water conditions and microbial processes interact in the Amazon. The study underscores the importance of considering both temperature and flooding when assessing methane dynamics in these ecosystems.

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Climate change is potentially increasing emissions from flooded areas while reducing the Amazon’s capacity to absorb the gas in upland forests

The study’s findings raised concerns about the potential for increased emissions from the Amazon. The Amazon’s unique role as both a major methane source and sink makes its response to climate change particularly significant for global greenhouse gas regulation.

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