| Popis: |
Nitrogen and phosphorus additions from various sources can change our aquatic systems, both through increased nutrient concentrations and changes in nutrient stoichiometry. Because bacteria are important in the cycling of nutrients and aquatic food webs, understanding how stoichiometry affects the bacterial community enhances our understanding of how these changes potentially affect aquatic ecosystems as a whole. This study examined the interactions between N:P ratios and sources and bacterial communities. To examine these interactions, a variety of methods were used. A field study was conducted at three sites along the Mahoning River. Both microcosm studies in the lab and mesocosm studies in the Aquatic Ecology Research Facility (AERF) were used to examine the effects of nutrient manipulations. These experiments used fluorescent in situhybridization (FISH) to determine the abundance of Domain Bacteria, alpha-, beta-, and gamma-proteobacteria as well as the Cytophaga-Flavobacteria(CF) cluster. Denaturing gradient gel electrophoresis (DGGE) was used in the mesocosm experiment to get a picture of the entire community. Finally, a competition experiment was conducted between two aquatic isolates, a B. cepaciaand a Flavobacteriumsp. A few relationships were seen between bacterial taxa and nutrients. The beta-proteobacteria were found in increased numbers under high N:P ratios. Whereas the CF cluster had lower numbers under high N:P ratios. Both the beta-proteobacteria and the CF responded more to ammonium than nitrate, however alpha-proteobacteria responded to nitrate more than ammonium. In the microcosm studies, there also appeared to be a change in the ammonium uptake and release. When ammonium was supplied in high concentrations, it was taken up by the bacterial community. When ammonium was not supplied, it was released by the bacterial community. Seasonal factors appeared to have a greater impact on all natural bacterial communities than nutrient manipulations. During the competition experiment, the both of the isolates had higher growth rates when combined than when separate. The Flavobacteriumalso showed a decrease in growth rates when supplied with nutrients in organic forms. Seasonal changes and carbon sources need to be studied more thoroughly to better understand their impact on the bacterial community and their interaction with nutrient effects. |
