Rainforests can buffer rising CO₂ in the short term—but this comes at a cost

Rainforests may be able to buffer rising carbon dioxide in the short term, but only by drawing harder on limited nutrients, according to a new study of Amazon understory forests.

Nature Communications published the paper on April 28. The researchers used open-top chambers in an Amazonian understory forest and simulated elevated atmospheric CO₂ by roughly 300 parts per million. They found that the extra CO₂ changed how roots in the forest floor searched for phosphorus, an essential nutrient.

Under elevated CO₂, litter-layer roots increased specific root length, while soil-based roots reduced productivity and showed higher arbuscular mycorrhizal colonization. The study also found a decline in soil organic phosphorus, suggesting the forest was tapping deeper into limited nutrient stores.

The result points to a short-term carbon-buffering effect: the forest can take up more carbon when CO₂ rises, but the gain comes with nutrient costs that may limit how far the benefit can go over time.

That matters because tropical forests are often discussed as a natural climate sink. This study suggests that the sink may be real, but not unlimited, and that phosphorus availability could determine how long rainforest buffering lasts.

Phys.org’s same-day coverage described the finding in similar terms, emphasizing that the short-term boost in carbon uptake is constrained by nutrient limits. The broader takeaway is that more CO₂ does not automatically translate into a durable long-term climate benefit for rainforest ecosystems.

The study does not settle how this effect scales across mature Amazon forests or how long the short-term response can persist. But it does add fresh evidence that rainforest carbon storage is tightly bound to soil chemistry as well as atmospheric change.