Prairie grasslands are very species rich but have declined in their extent considerably due to land-use change and exploitation. Many remaining prairie fragments are situated within an agricultural matrix and can be subjected to high levels of atmospheric ammonia deposition from animal units. Three prairie fragments in Minnesota that were located in close proximity to feedlots were selected, and 500-m transects were studied at an increasing distance from the feedlot. Changes in soil pH, soil nitrate concentration, and soil ammonium concentration with increasing distance from the source were variable between the sites, possibly due to differences in the processing of nitrogen in the soil and the degree of nitrogen limitation. Species richness showed significant negative relationships with ammonia deposition and soil nitrate concentration, whereas aboveground biomass showed a positive relationship with ammonia deposition. Both the richness and biomass of nongraminoid species declined with increasing soil nitrate concentration, whereas graminoid biomass was positively related to ammonia deposition and was negatively associated to richness. Bromus inermis, a non-native perennial grass, was the main species that increased at high deposition. The results of this study have important implications for the conservation and restoration of prairie grasslands.
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Acknowledgements A fellowship for CS to visit the University of Minnesota was jointly funded by The British Grassland Society Stapledon Memorial Fellowship and the British Council Researcher Exchange Program. The authors would like to thank J. Sullivan, C. Clark, T. Mielke, G. Brand, A. Ball, R. Hill, C. McFadden, Minnesota Pollution Control, and Minnesota Department of Natural Resources for assistance with this project. Thanks to E. Dorland for comments on an earlier version of this manuscript.
- Bromus inermis
- Nitrogen deposition
- Soil biogeochemistry
- Species richness