Amazon rainforest emits new stress-defense molecules during El Niño drought

Amazon rainforest emits new stress-defense molecules during El Niño drought Gaby Clark Scientific Editor Robert Egan Associate Editor The Amazon rainforest responded to the most severe drought ever recorded in the basin with an unexpected defense mechanism. Researchers at the Max Planck Institute for Chemistry in Mainz, Germany, found that during and after the intense 2023–2024 El Niño cycle, the most intense drought ever recorded in the region, vegetation significantly changed its chemical emissions to cope with environmental stress. The study was published in Communications Earth & Environment. Sesquiterpenes act as stress signals and protective compounds The research team measured the forest's release of biogenic volatile organic compounds, or BVOCs, which are carbon-based molecules naturally emitted by vegetation. The results were striking. While isoprene and monoterpenoid levels showed little influence from El Niño conditions of drought and heat, emissions of sesquiterpenes increased by 122% over the course of the event. Sesquiterpenes are reactive airborne molecules that trees produce as stress signals and protective substances. A well-known example is caryophyllene, a peppery-smelling compound found in cloves and black pepper. Even more surprisingly, the study detected unexpected emissions of less volatile sesquiterpene alcohols, including beta-eudesmol, alpha-eudesmol, and gamma-eudesmol, during the wet season after the drought peak. These findings suggest an adaptive response to oxidative stress, revealing how vegetation metabolically adjusts to adverse conditions. Interestingly, the change persisted long after the immediate stressor had passed. "Our results show that severe drought shifts the atmosphere toward lower-volatility and more reactive compounds," explains Joseph Byron, the study's first author and a researcher at the Max Planck Institute for Chemistry. "This reflects underlying metabolic changes as the rainforest attempts to mitigate damage from abiotic stress." Project leader Jonathan Williams added, "Between El Niño events, which occur every 2–7 years, the rainforest can revert to the original non-stressed emissions. However, climate models suggest that El Niño events will increase in frequency and intensity in this century, so these emissions may become a permanent feature of the region, altering the overlying atmospheric chemistry." Air samples collected directly above the forest canopy The researchers collected canopy air samples at the Amazon Tall Tower Observatory (ATTO), 150 km northeast of Manaus, Brazil. Using sorbent cartridges, they gathered samples every 1.5 to 3 hours at 23 meters on an 80-meter tower. In the laboratory in Mainz, they later analyzed them offline using gas chromatography and mass spectrometry. The findings build on earlier work by the same team on chemical indicators of stress in the Amazon rainforest. In their previous research, they identified specific mirror molecules, or enantiomers, that can serve as indicators of stress within the rainforest ecosystem. The current study expands this understanding by showing which specific reactive volatile compounds are produced directly as part of the forest's defense response during extreme climate events. Implications for climate change and rainforest resilience Understanding these chemical responses is very important, as climate change is predicted to make El Niño events more intense and persistent. The shift toward more reactive compounds could have significant implications for atmospheric chemistry and the overall resilience of the Amazon rainforest. Publication details Joseph Byron et al, Intense El Niño provokes production of new reactive volatiles as stress defences in Amazon rainforest, Communications Earth & Environment (2026). DOI: 10.1038/s43247-026-03597-7 Journal information: Nature Communications Earth & Environment , Communications Earth & Environment Key concepts effects of climate changedroughtsEl Nino-Southern OscillationClimate ChangeExtreme WeatherProvided by Max Planck Society