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Nitrogen availability effects on exotic, invasive plant species

dc.contributor.authorLowe, Petra N., author
dc.contributor.authorLauenroth, William K., advisor
dc.contributor.authorBurke, Ingrid C., committee member
dc.contributor.authorMilchunas, Daniel G., committee member
dc.description.abstractThe invasion of ecosystems by exotic plant species is a serious concern for land managers and conservationists. One of the most universally recognized exacerbating factors of exotic species invasions is disturbance. Human alterations to the global nitrogen cycle have increased atmospheric nitrogen deposition to terrestrial ecosystems worldwide, a disturbance that may encourage the growth of exotic invasive species that are uniquely capable of growing quickly when excess nitrogen is available. I undertook three experiments, one field and two greenhouse, to test the hypothesis that exotic invasive species are specifically adapted to take advantage of high nitrogen conditions, and outcompete natives as nitrogen availability increases, and that native species are better adapted to low nitrogen conditions and outcompete exotics when this nutrient is low. The field experiment examined the response of a disturbed short grass steppe community dominated by exotics to the addition of humus precursors and a labile carbon source intended to reduce plant available nitrogen. I was hypothesized that decreasing nitrogen availability would disadvantage the dominant exotic species and provide and advantage for the native species, returning the community to a vegetative structure more characteristic of undisturbed sites. Results of the experiment showed that decreasing nitrogen availability had no effect on native or exotic species density, richness, or basal cover. A greenhouse study investigated the response of above and belowground biomass, plant height, and nitrogen tissue concentrations of two species, the native Bouteloua gracilis, and the exotic Bromus tectorum, to a gradient in nitrogen availability and competition. The two species were grown under five levels of nitrogen availability and five levels of competition. I hypothesized that the native species would compete better at the low nitrogen levels, but competitive advantage would shift to the exotic as nitrogen availability increased, as some research has shown native species grow better than exotics at low nitrogen levels whereas exotics are only able to support their rapid growth rates when high amounts of resources are available. The exotic species was the better competitor at all nitrogen levels. A second greenhouse study investigated the above and belowground, height, and nitrogen tissue response of two native species, Bouteloua gracilis and Agropyron smithii, and four exotic species, Bromus tectorum, Euphorbia esula, Cirsium arvense, and Centaurea repens, to a gradient in nitrogen availability. I grew the six species individually under five levels of nitrogen availability. I hypothesized that the native plant species would gain more mass than the exotics at the low nitrogen levels, but the exotics would gain more mass at the high nitrogen levels. The native species failed to perform better than the exotics at the lowest nitrogen levels, but only two exotics performed better than the natives at the highest nitrogen levels. My results support the hypothesis that exotic species respond more readily to increasing nitrogen availability than native species, but do not support the hypothesis that all exotic species have a competitive advantage under high nitrogen conditions. Furthermore, my results do not support the hypothesis that native species have a competitive advantage over all exotic invasive weeds at low nitrogen conditions, as one of the exotics, Bromus tectorum, competed and grew comparatively better than the native species even at low nitrogen levels. The success of all exotic invasive weeds cannot be completely attributed to a rapid growth response to nutrient availability; it is likely that different species utilize a combination of strategies to outcompete native plant species.
dc.format.mediummasters theses
dc.publisherColorado State University. Libraries
dc.relationCatalog record number (MMS ID): 991008677239703361
dc.relationSB613.5.L68 2000
dc.relation.referencesBurke, Ingrid C., SGS-LTER Impact of Labile and Recalcitrant Carbon Treatments on Plant Communities in a Semiarid Ecosystem on the Central Plains Experimental Range, Nunn, Colorado, USA 1997-2012, ARS Study Number 3.
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dc.subject.lcshExotic plants
dc.subject.lcshPlants -- Effect of nitrogen on
dc.titleNitrogen availability effects on exotic, invasive plant species
dcterms.rights.dplaThis Item is protected by copyright and/or related rights ( You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). Ecosystem Science State University of Science (M.S.)


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