Washington, Feb 7 : A new study by ecologists has determined that nitrogen pollution is expected to steadily rise over the next century, with the most dramatic increases in rapidly developing tropical regions such as India, South America, Africa and Southeast Asia.
The study, conducted at the University of California, Irvine, found out that excess nitrogen in tropical forests boosts plant growth by an average of 20 percent.
Faster plant growth means the tropics will take in more carbon dioxide than previously thought, leading to an increase in atmospheric pollution in the regions.
For the study, LeBauer and Kathleen Treseder, associate professor of ecology and evolutionary biology at UCI, 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 the research team 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.
Scientists earlier believed added nitrogen would have little effect in the tropics because plants there typically have ample nitrogen and are constrained by low levels of phosphorus.
But if one necessary plant nutrient is in short supply - in this case phosphorus - plant growth will be poor, even if other nutrients such as nitrogen are abundant.
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.