Nitrogen pollution boosts plant growth in tropics by 20 percent

A study by UC Irvine ecologists finds that excess nitrogen in tropical forests boosts plant growth by an average of 20 percent, countering the belief that such forests would not respond to nitrogen pollution.

Faster plant growth means the tropics will take in more carbon dioxide than previously thought, though long-term climate effects are unclear. Over the next century, nitrogen pollution is expected to steadily rise, with the most dramatic increases in rapidly developing tropical regions such as India, South America, Africa and Southeast Asia.

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.

“We hope our results will improve global change forecasts,” said David LeBauer, graduate student researcher of Earth system science at UCI and lead author of the study.

The research results appear in the February issue of the journal Ecology.

Using data from more than 100 previously published studies, LeBauer and Kathleen Treseder, associate professor of ecology and evolutionary biology at UCI, analyzed global trends in nitrogen’s effect on growth rates in ecosystems ranging from tropical forests and grasslands to wetlands and tundra. Nitrogen, they found, 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. Although these are not the tropical forests that typically come to mind, they collectively account for more than half of the world’s tropical forests.

Scientists 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. 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. Experiments in the study added nitrogen at the high end of ambient nitrogen pollution to test the maximum potential response.

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,” LeBauer said. “Our study is a step toward understanding the far-reaching effects of nitrogen pollution and how it may change our climate.”

Source: University of California - Irvine

Related stories:

Microbe diet key to carbon dioxide release
As microbes in the soil break down fallen plant matter, a diet "balanced" in nutrients appears to help control soil fertility and the normal release of the greenhouse gas carbon dioxide into the atmosphere.
Scientists may have solved an ecological riddle
In a paper published this week in Nature, the authors – including Dr Ying Ping Wang from The Centre for Australian Weather and Climate Research – say that nitrogen fixation has long been recognised as an important process in controlling responses of many ecosystems – particularly boreal and temperate forests – to global environmental change.
Researchers explain nitrogen paradox in forests
Nitrogen is essential to all life on Earth, and the processes by which it cycles through the environment may determine how ecosystems respond to global warming. But certain aspects of the nitrogen cycle in temperate and tropical forests have puzzled scientists, defying, in a sense, the laws of supply and demand. Trees capable of extracting nitrogen directly from the atmosphere often thrive where it is readily available in the soil, but not where it is in short supply. Now scientists from the Carnegie Institution have explained the paradox by recognizing the role of two other factors: temperature and the abundance of another key element, phosphorous.
UC Davis researcher leads climate-change discovery
A team of researchers led by a first-year UC Davis faculty member has resolved a longstanding paradox in the plant world, which should lead to far more accurate predictions of global climate change.
Invading trees put rainforests at risk
To the list of threats to tropical rainforests you can add a new one — trees. It might seem that for a rainforest the more trees the merrier, but a new study by scientists at the Carnegie Institution warns that non-native trees invading a rainforest can change its basic ecological structure — rendering it less hospitable to the myriad plant and animal species that depend on its resources. Results are published in the Proceedings of the National Academy of Sciences.
Tropical plants go with the flow ... of nitrogen
Tropical plants are able to adapt to environmental change by extracting nitrogen from a variety of sources, according to a new study that appears in the May 7 early online edition of The Proceedings of the National Academy of Sciences.
Rotting leaf litter study could lead to more accurate climate models
Over the past decade, in numerous field sites throughout the world, mesh bags of leaf and root litter sat exposed to the elements, day and night, throughout the four seasons, gradually rotting away.
An Elephant Tail: New Method Tracks Endangered Critters
By analyzing chemicals in tail hair from elephants that wore radio collars, researchers tracked the diet and movements of elephants in Kenya – a method aimed at reducing human-elephant conflicts and determining where to establish sanctuaries to protect the endangered creatures.

News discussion:

Space & Earth science news