Extreme droughts in the Amazon rainforest are disrupting an important natural process that helps regulate Earth’s atmosphere, according to a new study by researchers at the Max Planck Institute for Chemistry. The findings reveal that severe heat and drought significantly reduce the rainforest soil ability to absorb isoprene, a naturally produced gas that plays a critical role in atmospheric chemistry and climate regulation.
The research, published in Communications Earth & Environment examined how rainforest soils behaved during the record breaking 2023 El Niño drought. Scientists monitored isoprene exchange between the soil and the atmosphere across multiple seasons at the Amazon Tall Tower Observatory (ATTO), one of the world’s leading tropical climate research sites.
Isoprene is a volatile organic compound released by plants, particularly in tropical forests. Every year, forests emit more than 500 million tonnes of this gas into the atmosphere. Under normal conditions, rainforest soils absorb a significant portion of the isoprene released by vegetation, helping maintain a delicate balance between plant emissions and atmospheric chemical reactions.
However, the new study found that this natural balancing mechanism weakens dramatically during extreme drought.
Researchers discovered that the soil’s ability to absorb isoprene dropped by more than four times during the 2023 El Niño event. As drought intensified and soil moisture fell below 20%, the microorganisms responsible for breaking down isoprene became much less active, sharply reducing the soil’s capacity to remove the gas from the atmosphere.
Lead author Giovanni Pugliese explained that during the extreme drought, rainforest soils no longer responded to rising levels of atmospheric isoprene. The findings suggest that the microbes responsible for consuming the gas experience physiological stress when the soil becomes too dry.
At the same time, drought causes trees to release even more isoprene into the air. According to project leader Jonathan Williams, the Amazon responds to heat stress by increasing isoprene emissions from its forest canopy while the soil simultaneously loses its ability to absorb the gas. This combination leads to a sharp rise in atmospheric isoprene levels.
Scientists believe plants produce additional isoprene as a protective mechanism against high temperatures and oxidative stress. While this helps vegetation survive extreme weather, it also creates broader consequences for the atmosphere.
Isoprene reacts with hydroxyl radicals and ozone, two key atmospheric oxidants that influence the breakdown of greenhouse gases. Higher isoprene concentrations reduce the atmosphere’s ability to remove methane, one of the most powerful greenhouse gases, allowing it to remain in the atmosphere for longer periods. The gas also affects the formation of secondary organic aerosols, tiny particles that act as cloud condensation nuclei and influence cloud formation and rainfall.
Previous experiments conducted in controlled rainforest environments had already shown that when soil moisture drops below approximately 19%, rainforest soils not only lose their ability to absorb volatile organic compounds but can actually begin releasing them back into the atmosphere. The latest field observations confirm that similar processes occur under real world drought conditions in the Amazon.
The researchers warn that increasingly frequent and intense El Niño events driven by climate change could further weaken this important natural climate feedback. Although scientists are still investigating whether soil microbes may adapt to hotter and drier conditions over time, the current findings highlight a growing vulnerability in one of Earth’s most important ecosystems.
To improve future climate predictions, the team says global climate models should include the role of rainforest soils in absorbing isoprene. Accounting for this process will help scientists better understand how tropical forests influence atmospheric chemistry, greenhouse gas lifetimes, cloud formation, and climate feedbacks as global temperatures continue to rise.
The research was carried out at the Amazon Tall Tower Observatory, a German Brazilian research project launched in 2009 and jointly managed by the Max Planck Institutes, Brazil’s National Institute of Amazonian Research (INPA), and the Amazonas State University (UEA). The findings add to growing evidence that climate driven droughts are altering the Amazon rainforest’s ability to regulate Earth’s atmosphere, making the protection of tropical ecosystems increasingly important in the fight against climate change.