Smithsonian Science » carbon dioxide

Scientists find excess nitrogen favors plants that respond poorly to rising CO2

John Barrat — Wed, 30 Jun 2010 17:09:21 +0000

As atmospheric carbon dioxide levels rise, so does the pressure on the plant kingdom. The hope among policymakers, scientists and concerned citizens is that plants will absorb some of the extra CO2 and mitigate the impacts of climate change. For a few decades now, researchers have hypothesized about one major roadblock: nitrogen.

Photo right: Scientist Adam Langley sprays plants in a test chamber with nitrogen. The additional nutrients changed the composition of the plants inside the chamber, spurring the growth of grasses that respond weakly to elevated levels of CO2.

Plants build their tissue primarily with the CO2 they take up from the atmosphere. The more they get, the faster they tend to grow—a phenomenon known as the “CO2 fertilization effect.” However, plants that photosynthesize greater amounts of CO2 will also need higher doses of other key building blocks, especially nitrogen. The general consensus has been that if plants get more nitrogen, there will be a larger CO2 fertilization effect. Not necessarily so, says a new paper published in the July 1 issue of Nature.

Adam Langley and Pat Megonigal, two ecologists at the Smithsonian Environmental Research Center, conducted a four-year study on plants growing in a brackish Chesapeake Bay marsh. In 2006 they began feeding sedge-dominated plots a diet rich in CO2 and nitrogen. Just as atmospheric CO2 levels are rising, so is nitrogen pollution in estuaries due farming, wastewater treatment and other activities. Because the sedge has previously shown a large CO2 fertilization effect, Langley and Megonigal expected that adding nitrogen could only enhance it.

Photo left: The Smithsonian’s Global Change Research Marsh is a tidal system. It sits on the western shore of the Chesapeake Bay in Edgewater, Maryland.

The sedge, Schoenoplectus americanus, initially reacted as expected. However, after the first year something unanticipated happened. Two grass species that had been relatively rare in the plots, Spartina patens and Distichlis spicata, began to respond vigorously to the excess nitrogen. Eventually the grasses became much more abundant. Unlike sedges, grasses respond weakly to extra CO2 and do not grow faster. Thus, the nitrogen ultimately changed the composition of the ecosystem as well as its capacity to store carbon.

The experiment unfolded on the Smithsonian Global Change Research Wetland, located on the Chesapeake’s western shore in Maryland. The Smithsonian site has a history of climate change research that dates back to the 1980s. For this study, Megonigal and Langley placed 20 open-top chambers over random plots of plants. The chambers were 6 feet in diameter and had 5-foot-tall transparent plastic walls.

Photo right: Open-top plastic chambers allow Smithsonian researchers to control and measure the amount of carbon dioxide and nitrogen that the plants receive.

The large, plastic pods allowed the scientists to manipulate CO2 concentrations in the air and nitrogen levels in the soil. Half of the plots grew with normal, background CO2 levels; the other half were raised in an environment with CO2 concentrations roughly double that amount. Similarly, half of the chambers were fertilized with nitrogen and the other half were untreated.

Langley and Megonigal began and ended each growing season with a census of the plants in each chamber. They noted the individual plant species, measured the above-ground biomass and the root growth. In the chambers that received the high-nitrogen diet, the plant composition changed dramatically; it went from 95 percent sedge in 2005 to roughly half grass in 2009. “It’s a fact that not all plants will be able to respond optimally to all changes,” said Megonigal. “The things they do respond to reflects their strategy for making a living in the environment.”

“The study underscores the importance of considering the mix of species when you’re trying to predict how terrestrial ecosystems will react to global climate change factors,” said Langley. Rising CO2 levels will favor some plants and excess nitrogen will favor others. This lesson will be important to understand as scientists consider additional global change factors such as precipitation, temperature and, in tidal wetlands, sea-level rise. The plant species that gain a competitive edge under these evolving conditions will determine how ecosystems respond to global change.

This study was supported by the U.S. Geological Survey and U.S. Department of Energy. The Smithsonian scientists recently received funding from the National Science Foundation that will sustain the research for another 10 years. Langley and Megonigal’s paper, “Ecosystem Response to Elevated CO2 Limited by
Nitrogen-Induced Plant Species Shift,” can be accessed on Nature’s website http://www.nature.com/nature/journal/v466/n7302/full/nature09176.html.

Smithsonian ecologists discover forests are growing at a faster rate

John Barrat — Mon, 01 Feb 2010 19:30:04 +0000

A new study published in the Feb. 2 issue of the Proceedings of the National Academy of Sciences indicates that forests in the Eastern United States are growing at a faster rate than at any time in the last 225 years. The chief culprit, researchers say, appears to be climate change, specifically: rising levels of atmospheric CO2, higher temperatures and longer growing seasons.

The study, conducted by Geoffrey Parker, a forest ecologist at the Smithsonian Environmental Research Center in Edgewater, Md., and Sean McMahon, a postdoctoral fellow at the Smithsonian Tropical Research Institute, utilizes data collected for more than 20 years by Parker from stands of mixed hardwood forest plots in Maryland. Data has revealed that the forests are adding an additional 2 tons per acre annually.

Photo left: Smithsonian forest ecologist Geoffrey Parker began his tree censuses his first day on the job, Sept. 8, 1987. Here he measures a tree on the grounds of the Smithsonian Environmental Research Center. (Photo by Kirsten Bauer)

Forests and their soils store the majority of the Earth’s terrestrial carbon. Small changes in the growth rate of the forest scientists believe, can have a significant impact on weather patterns, nutrient cycles, climate change and biodiversity.

In forest plots at SERC, Parker has meticulously tracked the growth of trees 5 to 225 years old. Data show that more than 90% of the stands grew two to four times faster than predicted from the baseline data.

By grouping the forest stands by age, McMahon and Parker were also able to determine that the faster growth is a recent phenomenon. If the forest stands under study had been growing this quickly their entire lives, the stands would be much larger than they presently are.

Photo right: Jess Parker, his colleagues and a team of citizen scientists have tagged more than 20,000 trees at the Smithsonian Environmental Research Center. These metal bands expand as the diameter of the tree increases, recording its growth. (Photo by Kirsten Bauer)

Parker began his tree census work Sept. 8, 1987—his first day on the job at the Smithsonian. He recorded and tracked trees 2 centimeters or more in diameter, identifing them to species and marking each tree’s exact coordinates on a map.

By knowing its species and diameter, McMahon, who specializes in data-analysis and forest ecology, is able to calculate the biomass of a tree. “Walking in the woods helps, but so does looking at the numbers,” he says.

“We made a list of reasons these forests could be growing faster and then ruled half of them out,” Parker says. The reasons that remained included increased temperature, a longer growing season and increased levels of atmospheric CO2.

Photo right: The tulip poplar, shown here, is a common tree in the temperate forests surrounding the Smithsonian Environmental Research Center. Other species include sweetgum, American beech, and southern red oak. (Photo by Kirsten Bauer)

During the past 22 years CO2 levels at SERC have risen 12%, the mean temperature has increased by nearly three-tenths of a degree and the growing season has lengthened by 7.8 days. The trees now have more CO2 and an extra week to put on weight. Parker and McMahon suggest that a combination of these factors has caused the forest’s accelerated biomass gain.

The findings are also important for policymakers trying to address climate change. Future carbon cap-and-trade rules will need to quantify the amount of carbon forests hold. If faster growth rates prove the norm, this could affect the formulas and the dollar value assigned to forests that are cut or conserved.

Parker and McMahon don’t expect SERC’s forest to continue growing at this accelerated rate forever. Some day the growth rate will level off. When that happens, they wonder how that will affect carbon dioxide levels. If trees are sponges that absorb CO2, what will happen to CO2 levels in our atmosphere when the trees become saturated? It’s a question for further exploration. In the meantime, Parker will continue walking through the SERC woods, tape measure in hand, carefully tracking the growth of the trees. –Tina Tennessen

Smithsonian to host online Climate Change conference Sept. 29-Oct. 1

John Barrat — Wed, 23 Sep 2009 12:17:34 +0000

The Smithsonian Center for Education and Museum Studies is hosting “Climate Change,” a three-day, free, education online conference Tuesday, Sept. 29 through Thursday, Oct. 1. This is the second in a series of Center for Educatin and Museum Studies conferences where researchers and curators from around the Smithsonian Institution come together to address a single subject.

“Climate Change” will feature sessions everyone will find thought provoking and relevant. Some sessions will be of special interest to educators while others will engage entire classrooms and the general public. Throughout the conference, participants will explore Smithsonian research and collections related to the evidence, impact and response to climate change. Alongside Smithsonian scientists and curators, the public will examine the issues surrounding climate change from the perspectives of science, history and art.

Photo: Scott Wing has used ginko fossils like this to estimate the amount of carbon dioxide in the atmosphere during the Eocene. (James DiLoreto)

“We’re excited to offer this online seminar on such an important and timely topic as climate change. The Smithsonian, with its experts, collections and partners is uniquely qualified to do so,” Wayne Clough, Secretary of the Smithsonian, says. “Our first seminar, on Abraham Lincoln, was a resounding success that started an online dialogue that continues today—here and abroad.” Presenters include:

*Bert Drake, senior scientist at the Smithsonian Environmental Research Center, who leads two major studies of the impact of atmospheric carbon dioxide on ecosystems;

*Don Moore, associate director for animal care at the Smithsonian’s National Zoological Park, who helps create conservation-management plans for wildlife; and

*Scott Wing, paleontologist at the Smithsonian’s National Museum of Natural History, who specializes in prehistoric plant life and its reactions to climate change.

The conference will show the depth of research that the Smithsonian is conducting on climate change. Smithsonian scientists and other experts will lead participants in explorations of Smithsonian research on this important issue via live presentations, moderated forums and demonstrations. Through live streaming, speakers will respond to questions and comments from the audience. All of the conference sessions will be recorded and archived and can be replayed at any time via the Web at www.SmithsonianEducation.org.

Registration is open to everyone at www.SmithsonianEducation.org/Climate.

This site also features a blog about climate change and an archive of the first online conference, “Abraham Lincoln,” which attracted more than 3,000 participants on six continents.

Fossils Show Prehistoric Global Warming

John Barrat — Fri, 22 May 2009 12:52:32 +0000

The Past as Prologue
For those who think that global warming is a 21st-century phenomenon, Scott Wing, a scientist at the Smithsonian’s National Museum of Natural History, has news about the past.

Wing headed an international team of scientists whose discovery of plant fossils in the Bighorn Basin of northwestern Wyoming helps document the consequences of a sudden global warming, called the Paleocene-Eocene Thermal Maximum (PETM), 55 million years ago.

Experts believe the PETM, which was caused by a massive release of carbon into the atmosphere, may be an analogue for what is happening today as humans burn increasing amounts of fossil fuel and release large amounts of carbon dioxide.

Plant Movement Signals Global Warming
For nearly 15 years, Wing and his team dug through sediments deposited during uplift of the Rocky Mountains, looking for fossils of the right age and condition. Their discoveries proved that warming caused major shifts in the distribution of plants, allowing southern-dwelling trees and shrubs, related to poinsettia, sumac, and paw-paw, to move some 1,000 miles north in less than 10,000 years. These subtropical invaders flourished for about 100,000 years in what we now know as Wyoming. As carbon dioxide levels dropped and temperatures cooled again, plants related to birches and bald cypress came to dominate the vegetation.

The study and interpretation of this fossil record helps other scientists project future changes in plant life that may result from global warming induced by human activity.