Washington, Feb 7 : A new study by ecologists has determined that excess nitrogen in tropical forests boosts plant growth by an average of 20 percent, with the most dramatic increases happening over the next century in rapidly developing tropical regions such as India, South America, Africa and Southeast Asia.
The study was conducted by LeBauer and Kathleen Treseder, associate professor of ecology and evolutionary biology at UCI (University of California, Irvine).
According to the study, faster plant growth means the tropics will take in more carbon dioxide than previously thought.
Nitrogen fertilizer, applied to farmland to improve crop yield, also affects ecosystems downwind by seeping into runoff water and evaporating into the atmosphere. Industrial burning and forest clearing also pumps nitrogen into the air.
For the study, the research team used data from more than 100 previously published studies to analyze global trends in nitrogen's effect on growth rates in ecosystems ranging from tropical forests and grasslands to wetlands and tundra.
What they found was that nitrogen increased plant growth in all ecosystems except for deserts.
Surprisingly, tropical forests that were seasonally dry, located in mountainous regions or had regrown from slash-and-burn agriculture also responded to added nitrogen.
According to the study, it is difficult to predict the long-term effects of nitrogen on global climate change.
One factor will be the degree to which humans change natural ecosystems, for example by cutting down or burning the tropical forests. Further, climate change may determine whether these areas grow back as forests or if they are replaced by grasslands or deserts.
It also is unknown how nitrogen will affect the fate of carbon once plants die and begin to decompose.
"What is clear is that we need to consider how nitrogen pollution interacts with carbon dioxide pollution," said LeBauer. "Our study is a step toward understanding the far-reaching effects of nitrogen pollution and how it may change our climate," he added.