The supply of nitrogen often limits the primary productivity of marine and terrestrial ecosystems. Consequently, understanding the processes that control the flux and transformation of nitrogen is of broad importance to ecology. Nitrification, the conversion of ammonia to nitrate, is a critical step in the nitrogen cycle that was thought to be carried out only by microorganisms belonging to the Domain Bacteria. However, a different group of microorganisms, Domain Archaea, were recently discovered to also be capable of this process, known as ammonia oxidation. Despite the ecological importance of ammonia oxidation, very little is known about the ecology of the organisms responsible. Additionally, since archaea were only recently discovered to be involved, their contribution to nitrification and their interactions with other nitrifiers remains unknown. This project will investigate interactions between ammonia oxidizing bacteria and ammonia oxidizing archaea in salt marsh sediments, using a combination of molecular, biochemical, and cultivation techniques. Preliminary studies indicate that the bacteria and archaea are differentially distributed among sites dominated by different marsh grasses. This project will test the hypothesis that this distribution reflects competition, niche differentiation and specialization by these two groups of microorganisms. Results from this study will help to elucidate fundamental ecological principles that drive the organization and activity of ammonia-oxidizing microorganisms and their impact on ecosystem functioning. These results will have broad significance to management and restoration of salt marshes, which play an important role in controlling nitrogen influxes to adjacent estuaries and coastal seas by trapping particulates and excess nitrogen. Another broader impact of this project involves its special focus on training undergraduates in research techniques and on recruiting more students from socio-economically disadvantaged backgrounds into the science curriculum at Connecticut College, a predominately undergraduate institution.
