That, in turn, is likely to dampen the ability of plants to offset increases in atmospheric carbon dioxide.
"We found that atmospheric carbon dioxide levels may rise even faster than anticipated, because ecosystems likely will not store as much carbon as had been predicted," said Peter Reich of the University of Minnesota, lead author of the study, which was conducted at the National Science Foundation (NSF)'s Cedar Creek Long-Term Ecological Research (LTER) site in Minn.
"As a result, soils will be unable to sustain plant growth over time [as atmospheric carbon dioxide continues to increase]," said plant ecologist David Ellsworth of the University of Michigan.
Estimating the role of terrestrial ecosystems as current and future sinks--or storage places--for excess carbon dioxide hinges on an ability to understand the complex interaction between atmospheric carbon dioxide and nitrogen in soils, the scientists believe.
The six-year study, the longest of its kind, sheds light on the relationship between carbon dioxide emissions and plant productivity. In the experiment, scientists grew 16 different grassland plants in 296 field plots. The plots were exposed to both ambient and elevated carbon dioxide levels, and varying levels of nitrogen.
The study was designed to document plants' ability to grow and flourish in nitrogen-depleted soil, which, scientists believe, will become more common as atmospheric carbon dioxide levels rise. Said Henry Gholz, director of NSF's LTER program, "Results from this research echo those of other studies of nitrogen's importance to trees and agricultural crops. I n the future, the effects of rising carbon dioxide on plants may become common throughout the world."
The Minn. study, with its range of species, provides a broad test of carbon dioxide and nitrogen interactions, said Reich. Previous studies have been done with a single or a few plant species.
The Cedar Creek LTER is one of 26 such LTER sites supported by NSF.