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'Nitrogen fixing' trees could help tropical forests bounce back, research suggests

2026-02-04 15:31
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'Nitrogen fixing' trees could help tropical forests bounce back, research suggests

On the narrow isthmus of Panama, scientists discovered adding nitrogen to the soil doubled tree growth, providing new insights into forest restoration.

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'Nitrogen fixing' trees could help tropical forests bounce back, research suggests

News By Corey Kane published 4 February 2026

On the narrow isthmus of Panama, scientists discovered adding nitrogen to the soil doubled tree growth, providing new insights into forest restoration.

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Photograph of a grassy hill with cows in the background and a tall tree. Many tropical forests are regenerating on land where forests have previously been chopped down for cattle grazing. Practices like these cause nitrogen to be lost from the soil, which can slow the regrowth of forests. (Image credit: Sarah Batterman / Cary Institute of Ecosystem Studies)
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An extra helping of nitrogen can double the growth of tropical trees in a recovering forest, vastly boosting the amount of carbon dioxide (CO2) they can absorb for a decade, according to a new study.

Researchers found that adding a nitrogen fertilizer to the soil in the youngest forests — those that had been pastures less than a year ago — increased their tree biomass by 95% compared with a non-fertilized control group. Ten-year-old forests also bounced back with the nitrogen treatment, showing a 48% increase in growth compared with the control group.

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Researchers with the Smithsonian Tropical Research Institute (STRI) tracked the growth of trees and woody vine lianas across a four-year period, monitoring how fertilizers of nitrogen, phosphorus or a combination of both would impact growth. Working in plots around the Panama Canal watershed, they also tested responses across a gradient of forest types, including areas that had been cattle pastures less than a year prior, 10-year-old recovering forests, 30-year-old recovering forests and 600-year-old forests.

For three months each year, field teams fertilized the trees at regular intervals. "You're driving up and down these steep hills to get to the field site," Batterman said. "And it's super beautiful. You can see the Panama Canal in the distance, with the big ships driving through. And then you're driving through this landscape of pastures with cows and some forests in different stages of recovery."

A team member spreads fertilizer on a recently abandoned pasture plot.

A team member spreads fertilizer on a recently abandoned pasture plot. White tubes mark locations in the plot so researchers can locate trees as they grow back. After four years, the trees in this plot were taller than the researchers, and the forest stored twice as much carbon when they had sufficient nitrogen compared to when they did not. (Image credit: Sarah Batterman / Cary Institute of Ecosystem Studies)

After hikes ranging from five minutes to an hour and a half, the field teams would fertilize the trees and measure their trunks. "It's superhot and sweaty, lots of mosquitoes and insects," Batterman said.

From the diameter of the tree trunks, researchers can extrapolate the aboveground biomass of the trees and, importantly, their carbon storage.

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The team's findings, published Jan. 13 in the journal Nature Communications, showed that nitrogen almost doubled growth in the areas that had been agricultural land until a year prior and boosted growth by almost 50% in forests that had been recovering for 10 years.

A root nodule on a legume tree where symbiotic bacteria fix nitrogen from the atmosphere into a form of nitrogen that the trees can use to grow.

A root nodule on a legume tree where symbiotic bacteria fix nitrogen from the atmosphere into a form of nitrogen that the trees can use to grow. Legume trees are abundant in tropical forests and can be used in reforestation efforts to naturally enrich the soil with nitrogen that speeds up carbon sequestration and storage. (Image credit: Sarah Batterman / Cary Institute of Ecosystem Studies)

Older forests showed no response to the extra nitrogen, and no forests showed a response to the phosphorus fertilizer.

When trees are harvested from tropical rainforests, the soil below is also degraded, with nutrients like nitrogen and phosphorus being depleted. This degradation is still detectable decades after deforestation.

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But rather than suggesting we physically fertilize vast tropical forests with nitrogen, the new findings can be used to plan forest recovery projects that prioritize tree species that can convert atmospheric nitrogen into a nutrient. This is known as "nitrogen fixing trees," study co-author Jefferson Hall, director of the Agua Salud project at STRI, which provided some of the forest plots where the experiment took place.

A tropical forest.

A tropical forest that is about thirty years old following deforestation and agricultural use. By thirty years, the forests show no evidence of nutrient limitation on carbon accumulation. Orange paint on tree trunks allows researchers to find and measure the same trees every year to track their growth and carbon storage. (Image credit: Sarah Batterman / Cary Institute of Ecosystem Studies)

"It's not practical that people are going to go out and, you know, fertilize all the forests of the world to capture CO2," Hall told Live Science. "The natural way of enhancing the nitrogen system would be to plant more nitrogen-fixing trees."

Richard Birdsey, a senior scientist at the Woodwell Climate Research Center who was not involved in the study, said the findings confirmed a long-standing observation about nutrients. "When I went to school, 50 years ago, the issue of nutrient depletion in tropical forests was known at that time. But no experiments like this had been done. It was simply some observations," he told Live Science.

Related stories

—Trees in Panama's tropical forests are growing longer roots in the face of drought

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Former tropical forests that had been removed, most often for agriculture, lack nutrients in the soil, and it often takes a long time for these nutrients to rebuild — even when the land is reforested. "The study, in a way, confirms these long-held beliefs about how tropical forests operate and what happens to them when they're harvested," Birdsey said.

Birdsey, who was with the U.S. Forest Service for over four decades, said recovering tropical forests are a vital global carbon sink, meaning they absorb more carbon than they release.

"They take up about 2.5 pentagrams of carbon per year," he said. "Globally, forests take up something like 3.5 pentagrams. So tropical forests, overall, are the biggest component of the carbon sink. And tropical regrowth forests, or regenerating forests, are the biggest part of the tropical forest sink."

Article Sources

Tang, W., Hall, J. S., Phillips, O. L., Brienen, R. J. W., Wright, S. J., Wong, M. Y., Hedin, L. O., Van Breugel, M., Yavitt, J. B., Hannam, P. M., & Batterman, S. A. (2026). Tropical forest carbon sequestration accelerated by nitrogen. Nature Communications, 17(1), 55. https://doi.org/10.1038/s41467-025-66825-2

Corey KaneCorey KaneLive Science Contributor

Corey Kane is a freelance reporter based in Panama City, Panama. He writes about science, environmental issues, immigration, politics and crime in the region. His work has appeared in EcoAmericas, the Tico Times, Al-Jazeera English and the Houston Chronicle. 

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