Smoke from wildfires provides an unexpected fertilizer to the Amazon rainforest

A new international study published today in Nature Geoscience has discovered a positive side effect of wildfires in the tropics: smoke carries phosphorus—a key nutrient for tree growth—into the heart of the Amazon rainforest. This influx of nutrients creates a fertilizing effect that can partially offset the carbon loss caused by fires and deforestation.

“Phosphorus is a limiting nutrient for tropical vegetation. When an additional supply arrives with the smoke, we observe an increase in photosynthesis and leaf growth; this allows the trees to make better use of sunlight and capture more atmospheric carbon,” explains the lead author, Adrià Descals, a Marie Curie researcher at the University of Antwerp and a researcher at CREAF and CSIC at the time of the study.

Specifically, each additional milligram of phosphorus per square meter translates, on average, into an annual increase of 7.4 grams of stored carbon. Given the vastness of the Amazon basin, this effect results in very significant amounts of carbon, "although it doesn't completely offset the emissions or ecological losses associated with fires and deforestation," Descals explains.

To conduct the research, the scientific team combined twenty years of satellite data (2001–2021), including direct indicators of vegetation photosynthetic activity, with field measurements and atmospheric models that simulate the long-distance transport of smoke. This approach allowed the researchers to identify a clear gradient: intact forest areas that receive more smoke exhibit higher productivity.

Most of the fires are concentrated in what is known as the 'arc of deforestation,' the area in the southern Amazon where logging and the use of fire to convert forest to agricultural land intensify during the dry season. According to the findings, the smoke travels thousands of kilometers from this region, carried by the wind, deep into the intact rainforest. The aerosols contained in the smoke, which include phosphorus among other compounds, are deposited on the forest floor through rain and ash, and are absorbed by the roots and leaves.

According to researchers, this does not mean at all that the increase in fires is 'good'. But it does show the extent to which ecosystems are strongly interconnected, even through air pollution, since, while fires release large amounts of carbon on a local scale, the smoke can increase the capacity of forests located hundreds or thousands of kilometers away to absorb CO₂.

“These results are crucial for improving climate models. If we want to accurately predict how tropical forests will slow global warming, we must take into account invisible factors such as the transport of nutrients through smoke,” concludes Josep Peñuelas, a CSIC researcher at CREAF and co-author of the study.

The article was led by Adrià Descals thanks to the Leonardo Grant awarded by the BBVA Foundation; it is also signed by Ivan Janssens, researcher at the University of Antwerp and co-director of his thesis, along with Josep Peñuelas.

Reference article: Descals, A., Janssens, I., Peñuelas, J., et al. (2026). Distant fires co-determine gross primary productivity in the Amazon rainforest. Nature Geoscience.