In an unprecedented study conducted during the record-breaking 2023–2024 El Niño event, scientists uncovered groundbreaking insights into how the Amazon rainforest responds chemically to severe environmental stress. This intense El Niño, which precipitated the most severe drought ever recorded in the Amazon basin, has prompted an extraordinary shift in the forest’s volatile organic compound emissions, revealing a complex and previously unrecognized defensive biochemical strategy in the world’s largest tropical forest.
Researchers from the Max Planck Institute for Chemistry in Mainz, Germany, meticulously analyzed air samples collected directly above the forest canopy at the Amazon Tall Tower Observatory (ATTO), situated approximately 150 kilometers northeast of Manaus. Utilizing an 80-meter measurement tower with sampling ports positioned at 23 meters above the canopy, the team employed sorbent cartridges to capture air samples every 1.5 to 3 hours. These samples were later subjected to rigorous offline analysis via gas chromatography coupled with mass spectrometry to quantify the presence and concentrations of biogenic volatile organic compounds (BVOCs).
The study’s central focus was on sesquiterpenes, a class of reactive carbon-based molecules produced by vegetation, which function as stress indicators and protective compounds. The data revealed a dramatic 122 percent surge in sesquiterpene emissions during the El Niño-induced drought period, a stark contrast to the relatively stable emission rates of other volatile compounds such as isoprene and monoterpenes. This selective amplification underscores the forest’s sophisticated metabolic response aimed at mitigating oxidative damage and enhancing resilience during periods of abiotic stress.
Sesquiterpenes are known for their chemical reactivity and role in atmospheric processes, with caryophyllene—a compound known for its distinctive peppery aroma and found in spices like cloves and black pepper—being a prototypical example. The elevated emission of these compounds implies a shift towards producing lower-volatility, more reactive molecules that may participate in complex atmospheric interactions. Such changes in volatile emissions influence not only the plants’ physiological state but also the broader atmospheric chemistry, potentially affecting cloud formation and regional climate dynamics.
Intriguingly, the study extended beyond the drought period, capturing data during the subsequent wet season. Researchers detected emissions of sesquiterpene alcohols, specifically beta-eudesmol, alpha-eudesmol, and gamma-eudesmol, which were not anticipated in such quantities during non-stressed periods. These sesquiterpene alcohols are less volatile than their hydrocarbon counterparts, suggesting a sustained activation of the forest’s defense metabolism well after the immediate environmental stress had abated. This persistence hints at a prolonged state of metabolic adjustment and recovery within the rainforest ecosystem.
The implications of these findings are profound, as they suggest that the Amazon rainforest possesses a dynamic capacity for biochemical adaptation that extends its defense mechanisms beyond the acute phase of stress. Joseph Byron, the study’s lead author, elucidated that the shift toward more reactive volatile compounds signifies a fundamental change in the forest-atmosphere interface, reflecting internal metabolic modifications as the ecosystem endeavors to cope with escalating drought stress.
Jonathan Williams, project leader at the Max Planck Institute for Chemistry, emphasized the broader climatic context, noting that while the rainforest typically rebounds between El Niño cycles—which occur every two to seven years—the intensification and increased frequency of these events projected under climate change scenarios could render such biochemical shifts a permanent feature. This permanent alteration in volatile emissions could lead to significant transformations in atmospheric chemistry, with cascading effects on regional climate patterns and ecosystem resilience.
The methodology incorporated cutting-edge analytic techniques to ensure the precision and robustness of the findings. Sampling directly above the canopy captures a representative snapshot of the BVOCs that ultimately influence local and regional air quality and chemistry. The use of gas chromatography-mass spectrometry (GC-MS) allowed for the detailed characterization of complex mixtures of volatile compounds, crucial for distinguishing closely related chemicals such as isomers and enantiomers implicated in plant stress responses.
This research builds upon prior studies by the same scientific team, which identified specific enantiomers—mirror-image molecules—as precise markers of stress within the Amazon ecosystem. The current work expands this understanding by pinpointing the exact reactive volatile compounds synthesized by the forest as part of a well-coordinated defensive response mechanism triggered by extreme climatic events. Hence, it underscores the interplay between atmospheric science, ecology, and plant physiology.
From a biogeochemical perspective, the pronounced increase in sesquiterpenes and sesquiterpene alcohols may lead to enhanced production of secondary organic aerosols (SOAs). These aerosols are critical components that influence cloud condensation nuclei, which in turn affect precipitation patterns. Thus, the chemical signature imprinted by stressed vegetation feeds back into the regional climate system, potentially altering rainfall regimes and ecosystem productivity in a feedback loop exacerbated by global warming.
The Amazon Tall Tower Observatory serves as a pivotal platform facilitating this research, operating as a collaborative German-Brazilian initiative involving the Max Planck Institutes for Biogeochemistry and Chemistry, the Brazilian National Institute of Amazonian Research (INPA), and the Amazon State University (UEA). Since its inception in 2009, ATTO has been instrumental in advancing the understanding of biogeochemical cycles, forest-atmosphere interactions, and climate dynamics in this megadiverse ecosystem.
Funding and support from multiple national and international agencies, including the German Federal Ministry of Education and Research (BMBF), Ministério da Ciência, Tecnologia e Inovações (MCTI), and Brazilian state organizations, underscore the global recognition of the Amazon’s critical role in climate regulation and biodiversity conservation. The integration of interdisciplinary expertise across atmospheric chemistry, ecology, and environmental physics continues to propel breakthroughs in understanding the complex responses of tropical forests to climate extremes.
This seminal study not only unravels previously uncharted biochemical strategies employed by rainforest vegetation to combat oxidative stress caused by intense drought but also signals critical shifts in the ecological and atmospheric dynamics of the Amazon. As climate models forecast escalating severity and frequency of El Niño events, these findings furnish valuable insights into the adaptive capacity of tropical forests and highlight the urgent need for sustained monitoring and research to better predict and mitigate climate change impacts on these vital ecosystems.
Subject of Research: Not applicable
Article Title: Intense El Niño provokes production of new reactive volatiles as stress defences in Amazon rainforest
Web References: http://dx.doi.org/10.1038/s43247-026-03597-7
Image Credits: Dom Jack, Max Planck Institute for Chemistry
Keywords
Amazon rainforest, El Niño, drought stress, sesquiterpenes, biogenic volatile organic compounds, atmospheric chemistry, oxidative stress, reactive volatiles, climate change, Amazon Tall Tower Observatory, gas chromatography-mass spectrometry, tropical forest resilience
