Effects of soil nitrogen enrichment on the germination, biomass production, and development of plant communities in the Lake Michigan sand dunes
Sand dunes along the southern shores of Lake Michigan annually receive deposition of atmospheric nitrogen (N) at amounts exceeding 14 kg ha-1. Such deposition has been reported to alter vegetation and reduce species diversity in plant communities. I predicted that atmospheric deposition of N to herbaceous plant communities of the Lake Michigan sand dunes would increase seed germination, biomass production, and the dominance of grass species, leading to reduced diversity. To test these predictions, the effects of soil ammonium nitrate (NH4NO3) enrichment on seed germination, biomass production, and species composition of nine native prairie species were investigated. Germination and biomass experiments were conducted at the Purdue University Calumet greenhouse and changes in species composition were monitored in field plots located within the Indiana Dunes National Lakeshore, for three (2010-2012) years. Changes in vegetation were analyzed with Detrended correspondence Analysis (DCA) ordination. Addition of NH4NO3 increased seed germination and total biomass production in six of the nine species investigated. Field plots were dominated by grass species Schizachyrium scoparium (Michx.) Nash. and Panicum virgatum L. The relative importance of forbs (Monarda punctata L. and Lupinus perennis L.) increased in control plots, but was reduced in all NH4NO3 treatment plots. Ammonium nitrate additions increased dominance of S. scoparium, and reduced species diversity. DCA ordination revealed a clear divergence of vegetation in treatment and control plots. The results of these NH4NO3 experiments suggest that chronic deposition of atmospheric N will likely reduce the diversity of plant communities in the Lake Michigan sand dunes.
Choi, Purdue University.
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