Spatial differences in denitrification and bacterial community structure of streams: relationships with environmental co
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Aquatic Sciences
RESEARCH ARTICLE
Spatial differences in denitrification and bacterial community structure of streams: relationships with environmental conditions Alyssa M. Baxter • Laura Johnson Todd Royer • Laura G. Leff
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Received: 27 January 2012 / Accepted: 31 July 2012 / Published online: 21 August 2012 Ó Springer Basel AG 2012
Abstract In streams, benthic bacterial communities are integral to multiple aspects of ecosystem function, including carbon and nitrogen cycles. Variation both in terms of bacterial community structure (based on taxonomic and/or functional genes) and function can reveal potential drivers of spatiotemporal patterns in stream processes. In this study, the abundance and diversity of 16S rRNA genes and abundance of nosZ genes, encoding for nitrous oxide reductase, were related to denitrification and environmental conditions. Denitrification rates varied among the three streams examined, and within a given stream there were significant longitudinal differences. Likewise, bacterial community structure based on analysis of the 16S rRNA gene also differed significantly among streams. However, variation in denitrification rate was not well correlated with environmental or biological variables measured. In addition, relatively large numbers of denitrifiers occurred when denitrification rates were low. In conclusion, although the streams differed in environmental conditions as well as bacterial community structure, these differences did not explain much of the spatial variation in denitrification rates. Keywords Streams Denitrification Bacterial communities
A. M. Baxter L. G. Leff (&) Department of Biological Sciences, Kent State University, Kent, OH 44242, USA e-mail: [email protected] L. Johnson T. Royer School of Public and Environmental Affairs, Indiana University, 1315 E. Tenth St., Bloomington, IN 47405, USA
Introduction Denitrification, the microbially mediated reduction of nitrate to a nitrogenous gas, is an integral part of the global nitrogen cycle; conditions energetically favorable for denitrification are common in streams (e.g., Mulholland et al. 2008, 2009). Because of the ecological importance of this process, past studies have sought to explain spatiotemporal variations in lotic denitrification rates based on environmental data (Arango and Tank 2008; Inwood et al. 2005; Mulholland et al. 2008, 2009) and broad, general variables related to the microbial community, such as ecosystem respiration (Mulholland et al. 2008). Understanding the relationships between these variables is important for predictions of how biogeochemical processes will respond to changing environmental conditions (Schlesinger et al. 2006). Basic factors required for denitrification are nitrate, organic matter, and anoxia. Typically, nitrate concentration is among the environmental variables that often correlates with denitrification rates in streams (Martin et al. 2001; Inwood et al. 2005; Arango and Tank 2008; Mulholland et al. 2009). Dissolved organic carbon (DOC) availability, because of its importa
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