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.
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
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