SGER: Stable Isotopic Determination of Microbial Carbon Sources In Streams

University Of Arkansas, Fayetteville AR

Investigators

Abstract

The main objective of the proposed research is to develop and test the use of the stable carbon isotope composition of bacterial phospholipid fatty acids (PLFA) for the investigation of microbial carbon sources in streams. The question of how well the isotopic composition of organic matter sources in streams can be resolved over different spatial and temporal scales remains unanswered. Additionally, the stable carbon isotope composition of bacterial PLFA is a new method that has yet to be related to dissolved organic matter (DOM), a more challenging task due to the heterogeneous composition of compounds of varying isotopic composition that form DOM. The proposed research will establish the use of the proposed approach for investigating biogeochemical processes of stream ecosystems. The specific objectives of the proposed research will be to determine: (1) the relationship between the stable carbon isotope composition of bacterial PLFA and DOM, (2) the separation in the stable carbon isotope composition of allochthonous versus autochthonous materials across spatial and temporal scales within streams, and (3) how the stable carbon isotope composition of organic matter and bacterial PLFA are related in streams. The objectives of the study will be accomplished through both laboratory and field investigations of the isotopic composition of DOM, bacterial PLFA and organic matter sources in two stream ecosystems with contrasting watersheds. The relationship between the stable carbon isotope composition of DOM and the PLFA of both free and attached bacteria will be determined in experiments of natural assemblages of stream bacteria in both enrichment cultures and glass bead bioreactors grown on different sources of stream DOM. These experiments will represent the first studies to investigate the isotopic composition of individual fatty acids of natural assemblages of bacteria in relation to DOM. The ability to determine the source of carbon fueling bacterial activity would advance understanding of the biogeochemical cycling of DOM in the aquatic environment, and the linkage between DOM composition and microbial food web dynamics.