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How one group of plants help regrow an entire forest

A team of researchers report in Nature that legumes grow faster than other trees in the earliest phase of a forest’s re-growth, pumping into the soil enough nitrogen to support the rest of the forest's burgeoning plants.

Cattle graze in farmland in Palmas Bellas, Panama, that had been forest about thirty years earlier. Researchers now report in Nature that one variety of plants plays a critical role in helping a pulled-down forests in Panama make a comeback.

Mary Knox Merrill/The Christian Science Monitor

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Legumes rise to meet the challenge of deforestation, scientists have found.

A team of researchers report in Nature that legumes, which fix atmospheric nitrogen into a useable form for other plants, grow faster than other trees in the earliest phase of a forest’s re-growth. The find highlights the pivotal role that just one group of plants – in collaboration with some useful bacteria – plays in growing up an entire forest that, as a carbon dioxide absorber, ultimately becomes the entire planet’s ally against global warming.

“This is a group of species that are helpers to the rest of the forest,” says Lars Hedin, a professor at Princeton University and a co-author on the paper.

“It’s super cool,” he adds.

For decades, the Americas’ forests, once unfurling like rumpled blankets across the continent, have been cut into to make room for booming cities and sprawling commercial farms and ranches. Those cuts, scientists note, have brought about the extinction of an unknown amount of species, as well as troubling losses in the ranks of an efficient carbon dioxide reducer: the tree.

Forests, as it is now well known, are prodigious sappers of the atmospheric carbon dioxide that would otherwise contribute to global warming. And as countries now work to replace the forests, bean or seed producing plants called legumes have been increasingly fingered as critical to the success of those efforts.

It has long been known that legumes are nitrogen fixers, converting atmospheric nitrogen into a soil-based version that plants depend on for growth, since tropical soil is, on its own, nitrogen-poor. The process begins with bacteria called rhizobia that take up residence in the plant’s root nodules (pods inside the tree's roots) to feed on the carbohydrates the plant manufactures. At the same time, the bacteria sequester nitrogen from the air and fix it into a form palatable to plants. Excess nitrogen in that process is churned into the soil, to the benefit of non-nitrogen-fixing plants.


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