Effects of nitrogen fertilizer on the composition of two prairie plant communities

Piper, J. K.; Billings, D. N.; Leite, V. J.

Effects of nitrogen fertilizer on the composition of two prairie plant communities

2005

Piper, J. K. | Billings, D. N. | Leite, V. J.

In recent decades, nitrogenous compounds, arising from various anthropogenic sources, have become significant components of precipitation and have been shown to have some profound effects on both species richness and dominance of some plant communities. To examine how nitrogen addition can affect the species composition of Central Great Plains prairie plant communities, we applied N fertilizer at five levels for each of five consecutive years at two sites in south-central Kansas with similar rainfall and temperature regimes. One site was a tallgrass prairie and the other was a sand prairie community. The treatments consisted of N additions at the rate of 0, 5, 10, 20, and 40 g N/m<sup>2</sup> in the form of solid urea. Within permanent plots, we monitored annually species richness and evenness, and percentage cover by cool-season graminoids, N-fixing species, and annual/biennial species. All these measures varied considerably among years at both sites, but N treatment effects were evident at the sand prairie site only. At the sand prairie, in general species richness and percentage cover by legumes declined with N addition. Moreover, species were excluded non-randomly from N addition plots, with several species apparently particularly intolerant of N addition. The results reinforce a relationship, observed in Europe and the northern Great Plains, between N addition and plant biodiversity decline in grassland communities, and may point to a serious conservation concern for rare species under a chronic regime of N-enhanced precipitation.

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