Flow velocity and primary production influences carbon utilization in nascent epilithic stream biofilms
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In small streams, the majority of carbon turnover is due to microbial activity in biofilms. Flow velocity is a key factor influencing biofilm function, and nascent biofilms with high energy need for growth might be especially sensitive to hydrodynamics. The major part of carbon supply is allochthonous but algae can provide easily available exudates for biofilm bacteria. In this study, epilithic biofilms were grown for 2 weeks in a third order stream in Thuringia, Germany, and then incubated in replicate flow channels in climate-controlled chambers. Glucose and arbinose were added immediately to all channels, and the effects of flow velocity and light availability on rates of sugar removal were examined. Phosphate addition did not influence sugar decrease rates. Flow velocities of either 0.3 m s−1 or 0.7 m s−1 resulted in 1.3 to 3.1 times higher decrease rates under the higher flow velocity. Light exclusion resulted in a 2.2 to 2.6 times faster sugar decrease but only a 0.5 times dissolved organic carbon increase compared to channels with light input, suggesting a strong internal coupling of primary producers and heterotrophs. Our results indicate that carbon uptake from the water column is fostered at higher flow velocities and that primary production is an important internal carbon source in nascent epilithic biofilms.
KeywordsGlucose Arabinose Sugar uptake Light Bacteria Flumes
The authors are thankful to Anne Huchel, Andrea Scheibe and Pascal Weigand for assistance in both field and laboratory, and two anonymous reviewers for their helpful comments. Sven Rau provided excellent technical support for the phosphatase activity measurement. This work was supported by a grant from the Deutsche Forschungsgemeinschaft DFG (266/3).
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