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Nitrogen Dynamics in the Sagebrush Steppe: Anthropogenic Fluxes Affect Shrub-Steppe Plant Communities
Department: Biology
Specimen Elements
Unknown to Unknown
Roger Long
Idaho State University
City: Pocatello
ABSTRACT We sampled vegetation cover, biomass, and diversity on two ostensibly similar sagebrush-steppe sites at the Idaho Nuclear Laboratory in east-central Idaho, USA, to elucidate effects of livestock grazing on cold desert plant communities, and possible effects of nutrient transfer from adjacent agricultural fields. We sampled 107 quadrats on two sites, one currently grazed and one that has not been grazed by livestock in ~70 years. We determined that plant cover, biomass, and diversity were all higher on the ungrazed site, although species richness was greater on the grazed site. We used stable isotope analysis of plant tissues to identify nitrogen isotopic signatures of sage-steppe plant species, and to determine constraints to nitrogen availability for herbivores in ecosystems adjacent to agricultural fields. We sampled vegetation for analysis at two ostensibly similar sagebrush-steppe sites adjacent to agricultural (alfalfa and wheat) fields in Central Idaho, USA, with different grazing regimes: one ungrazed by livestock for ~70 years; and one with historical and current grazing. Three shrub species, big sagebrush (Artemisia tridentata), dwarf goldenbush (Ericameria nana), and winterfat (Krascheninnikovia lanata); and two grasses, Indian ricegrass, (Achnatherium hymenoides) and squirreltail grass (Elymus elymoides), were sampled at 100-m intervals to a distance of 2 km from the edge of agricultural sites. Our findings were that the grazed site was more nitrogen limited than the ungrazed site, and plants occurring at greater distances from agricultural fields also were increasingly nitrogen limited. We used Principal Components Analysis (PCA) to determine the contributions of the 15N and C:N characteristics of plant species under consideration in distinguishing sites and xiv distances from fields. In those analyses, we observed that 15N was strongly associated with site (grazed or ungrazed) and, to a lesser degree distance from agricultural fields, whereas C:N was more associated with distance than site. Based on these results, we hypothesize that the differences in plant communities we observed between the two sites is the result of nitrogen export from the grazed site in the form of livestock biomass.

Nitrogen Dynamics in the Sagebrush Steppe: Anthropogenic Fluxes Affect Shrub-Steppe Plant Communities

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