Higher carbon dioxide, lack of nitrogen limit plant growth

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"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.

Scientists study purple lupines and other flowers and grasses in an experimental plot (Photo: Jason West, University of Minnesota)

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, "The possibility that nitrogen availability will limit the stimulating effect on plant productivity expected as a result of higher atmospheric carbon dioxide concentrations has important consequences. Reich et al. provide convincing results from long-term studies of Midwestern prairie species under controlled experimental conditions that this will be the case under low-nitrogen conditions. Since the results are consistent with those from other studies of trees and agricultural crops, this suggests that nitrogen limitations in the future may be common in much of the world, despite widespread nitrogen pollution."

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.


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