In our increasingly carbon-rich atmosphere, the growth of the Amazon rainforest may be limited by a lack of phosphorus in the soil, new research suggests.
Higher concentrations of carbon dioxide (CO2) cause plants to grow faster, which means they store more carbon.
This storage—especially in large forests like the Amazon—helps limit rising carbon dioxide levels and slow climate change.
operate
However, plants also need nutrients to grow, and new research suggests that the availability of a specific nutrient, phosphorus, may limit the Amazon’s ability to increase productivity (growth rate) as carbon dioxide increases. It could also make tropical rainforests less resilient to climate change, the researchers warn.
The study was published in the journal natureconducted by an international team led by Brazil’s National Institute of Amazonian Research (INPA) and the University of Exeter.
Lead author Dr Hellen Fernanda Viana Cunha from INPA said: “Our results question the current potential of the Amazon to maintain high carbon uptake rates.”
“About 60 percent of the Amazon basin is located on older soils that are low in phosphorus, but the role of phosphorus in controlling productivity is unclear, as most fertilization experiments in other parts of the world have been conducted in systems with higher phosphorus levels .
“Our experiment, Amazon Fertilization Experiment (AFEX), examining the effects of adding phosphorus, nitrogen and base cations (other potential key nutrients) in an ancient low phosphorus area of the rainforest.
“Only phosphorus improved productivity in the first two years of the experiment. Such a rapid and strong response to phosphorus above and below ground indicates that the entire system was operating under severe phosphorus limitation.”
productivity
Soils in tropical regions like the Amazon are often formed millions of years ago, and some nutrients may be lost over time.
While microbes associated with certain plants and soils can absorb nutrients like nitrogen from the air, phosphorus is not available as a gas in the atmosphere—so once depleted, levels have little chance to increase.
In the new experiment, two additional years of phosphorus resulted in a significant increase in fine root growth (29 percent) and canopy productivity (19 percent).
Stem growth did not increase. This may be because roots and leaves require more phosphorus than stems, which are a slower process, Dr. Cunha said.
