Why Do Tropical Forests Release So Much Nitrogen Back into the Atmosphere?

In findings that could influence our understanding of climate change, a Princeton research team has learned that tropical forests return to the atmosphere up to half the nitrogen they receive each year, thanks to a particular type of bacteria that lives in those forests.

The authors aimed at answering the following question: Why do tropical forests release higher levels of nitrogen than temperate biomes, and why is there a decrease in nitrogen with increasing rainfall? Authors remarked that this trend has been reported, for example in Hawaiian rainforests, "but never conclusively explained".

Scientists fount that bacteria, referred to as "denitrifiers," exist in forest soil, where they live by converting the nitrates fed upon by tree roots back into nitrogen gas, which is lost to the atmosphere. The researchers who recently discovered this behavior say the findings are important for our understanding of how tropical forests fit into the earth's climate system.

"Tropical forests play a major role in regulating the planet's climate, and these findings indicate that we are still working on our basic understanding of the nitrogen cycle," said Lars Hedin, a researcher on the team and professor of ecology and evolutionary biology at Princeton. "That a group of bacteria can have such a dramatic impact on forest nutrition debunks our previous theories about how nitrogen behaves in forests, and shows us that these microorganisms affect soil nutrients and forest growth."