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Influence of Nitrogen Loading and Species Composition on the Carbon Balance of Grasslands
1D. A. Wedin, Department of Botany, University of Toronto, Toronto, Ontario M5S 3B2, Canada. D. Tilman, Ecology, Evolution and Behavior, University of Minnesota, St. Paul, MN 55108, USA.
Abstract:
In a 12-year experimental study of nitrogen (N) deposition on Minnesota grasslands, plots dominated by native warm-season grasses shifted to low-diversity mixtures dominated by cool-season grasses at all but the lowest N addition rates. This shift was associated with decreased biomass carbon (C):N ratios, increased N mineralization, increased soil nitrate, high N losses, and low C storage. In addition, plots originally dominated by nonnative cool-season grasses retained little added N and stored little C, even at low N input rates. Thus, grasslands with high N retention and C storage rates were the most vulnerable to species losses and major shifts in C and N cycling.