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Updated 10:00 AM April 17, 2006




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Emissions are degrading soil's ability to foster plant growth

Rising carbon dioxide levels in the atmosphere over time will lead to nutrient limitations to grassland productivity, according to a study by researchers at U-M and the University of Minnesota.

An article published in the journal Nature April 13, which is based on a six-year study—the longest known study of its kind—says that decision-makers need to understand the relationship between fossil fuel emissions and plant productivity and nutrients when they set policy. Grasslands amount to about 30 percent of the arable land surface of the world.
David Ellsworth, associate professor of plant ecophysiology at the School or Natural Resources and Environment, studies carbon dioxide levels and grassland productivity at the Cedar Creek Natural History Area in central Minnesota. (Photo courtesy SNRE)

"The results suggest that our ecosystem likely cannot get enough nutrients under elevated levels of CO2," says David Ellsworth, associate professor of plant ecophysiology at the School of Natural Resources. "As a result, we think that the soil will be unable to sustain growth and productivity increases from enriched CO2 over time."

At Cedar Creek Natural History Area in central Minnesota, the researchers grew 16 native or naturalized plant species in two types of plots. The soil in one plot was enriched with nitrogen while the soil in the other was not. The purpose of the study was to document the plant's ability to grow biomass and flourish in a nutrient-poor soil as carbon dioxide levels increased to concentrations likely to be reached by the middle of this century.

The study's results are consistent with previous experimental studies of the interaction between carbon dioxide and nitrogen in agricultural and forest plantation systems, Ellsworth says. "This suggests that there may be no 'free-lunch' of nitrogen for plants under CO2 enrichment for this long," he says.

With a wide range of species types and combinations, including mixtures, the study provides a broad test of carbon dioxide and nitrogen interactions under contrasting low and high nitrogen supply rates. It also includes measurements of root biomass. Previous studies had been done with a single or a few types of plant species. These studies had greater amounts of nitrogen added and included no below-ground biomass measures.

The article, "Nitrogen limitation constrains sustainability of ecosystem response to CO2," was written by Ellsworth and co-authors Peter Reich, Sarah Hobbie, Tali Lee, Jason West, David Tilman, Johannes M.H. Knops, Shahid Naeem and Jared Trost.

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