Intense El Niño provokes production of new reactive volatiles as stress defences in Amazon rainforest

Why this matters for our future climate

The Amazon rainforest is often called the lungs of the planet, but it is also a giant chemical factory that quietly steers clouds, rain and climate. This study asks what happens to that factory when an intense El Niño brings record-breaking heat and drought. By tracking invisible gases released by trees before, during and after the 2023–2024 El Niño, the authors show that the forest changes the type of chemicals it breathes out, switching into a kind of stress mode that could alter both its own health and the atmosphere above it.

A forest under growing pressure

The Amazon normally recycles moisture into the air and locks away vast amounts of carbon. Yet rising temperatures, repeated droughts and fires are pushing parts of the forest toward becoming a source of carbon rather than a sink. Trees also release a small fraction of their carbon as volatile organic compounds, or VOCs, which help form airborne particles and clouds. Among these are isoprenoids, a family of plant scents that includes lighter, more common molecules and heavier, rarer ones. Although the heavier gases are scarce, they react very quickly in air and may strongly influence how new particles and clouds form over the forest.

Following the forest through an extreme El Niño

The researchers took detailed measurements of these plant gases from a tall tower deep in the central Amazon, spanning four key moments: a normal wet season before El Niño, the peak drought, a wet season still influenced by El Niño, and the following dry season after conditions eased. They combined careful sampling with advanced laboratory analysis, and also recorded temperature, humidity, soil moisture, light and ozone. As expected, the El Niño period brought hotter air, drier soils and much lower humidity. Ozone in the forest air also rose sharply during the driest months, a sign of stronger atmospheric chemistry at work.

A chemical pivot toward heavier stress gases

Not all plant gases responded in the same way. The more familiar isoprene and standard monoterpenes mostly followed the seasons, rising in dry months and falling in wet ones, rather than directly mirroring El Niño. In contrast, the heavier sesquiterpenes rose by more than 100 percent across the El Niño cycle. Most strikingly, during the wet season that followed the peak drought, the team detected a new group of even less volatile sesquiterpene alcohols in the air, including several compounds rarely, if ever, reported above intact rainforest. Their levels were comparable to the regular sesquiterpenes, suggesting that these newly seen gases briefly became a major part of the forest’s chemical output.

Signs of a stress-activated defence pathway

By examining which compounds rose and fell together, the authors uncovered a tightly linked cluster of sesquiterpenes and sesquiterpene alcohols that share a common carbon skeleton. These gases peaked in the mornings, when plant water flow and evaporation were strongest, and dropped rapidly at midday, implying that their release is controlled mainly by plant metabolism rather than simply being destroyed in the air. Calculations showed that changes in atmospheric chemistry alone could not explain their surge; the trees must have ramped up production. The pattern points to a metabolic pathway that turns on under severe heat and drought, then continues into the next wet season when water returns, before fading once the stress eases.

What this means for the forest and the sky above

The authors propose that these heavier, more reactive gases form part of a stress defence system, helping plants cope with harmful oxygen-containing molecules that build up in their tissues during extreme conditions. Because these vapors are stickier and less volatile, they may also be especially good at forming new airborne particles, subtly reshaping the mixture of chemicals and particles over the Amazon during and after droughts. As strong El Niño events and heatwaves become more common with climate change, the study suggests that the Amazon’s atmospheric “breath” may shift toward a greater share of these heavy stress gases, with consequences for cloud formation, rainfall patterns and the resilience of the forest itself.

Citation: Byron, J., Pugliese, G., de A. Monteiro, C. et al. Intense El Niño provokes production of new reactive volatiles as stress defences in Amazon rainforest. Commun Earth Environ 7, 419 (2026). https://doi.org/10.1038/s43247-026-03597-7

Keywords: Amazon rainforest, El Niño, volatile organic compounds, drought stress, atmospheric chemistry