Microbial Transformations and Fate of Vascular Plant Detritus in Aquatic Ecosystems

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Bacterial metabolism often dominates energy and nutrient flow in aquatic ecosystems and thereby has a major impact on biogeochemical cycles as well as food webs. There are numerous potential sources of nutrients fueling bacterial metabolism, but in many rivers and estuaries detrital material derived from vascular plants is likely to be of major importance. This research will determine rates of bacterial production and respiration in a variety of systems including the Amazon River and several estuaries on the south Texas coast. The sources of organic matter fueling bacterial growth and the chemical identity of this material will be investigated using stable isotope (C & N) compositions, solid-state 13C nuclear magnetic resonance (NMR) and source-specific biomarker compounds. Dissolved organic matter (DOM) is thought to fuel most of the microbial heterotrophic production in these systems, and it appears likely that vascular plants contribute significantly to this pathway of nutrient flow. In the proposed research the production, microbial transformations and fate of DOM derived form avariety of plant materials will be investigated during long-term (2-3yr) decomposition studies. Diagenetic changes in the chemical and stable isotope compositions of both the particulate and dissolved components will be determined. The project team is well qualified. Institutional accommodations are good. Collaboration and coordination with other work in progress will be productive.