Urban stream denitrifier communities are linked to lower functional resistance to multiple stressors associated with urbanization
The microbial communities in urban stream ecosystems are subject to complex combinations of stressors. These same microbial communities perform the critical ecosystem service of removing excess reactive nitrogen. We asked whether the denitrifying microbial communities in urban streams differ in their functional resistance to common urban stressors from communities from nonurban streams. We exposed inocula from a highly polluted urban stream and a nearby nonurban stream to three different stressors, added alone and in combination. Stressors represent the common urban impacts of thermal pollution (10°C), trace metal exposure (ionic silver (Ag+)), and salinization (addition of NaCl). We used reduction in nitrite (NO2 −) concentrations under anaerobic conditions as a proxy for denitrification potential. Nonurban stream denitrifying microbial communities were more diverse than their urban counterparts. Denitrification potential for both communities was unaffected by exposure to any individual stressor. However, denitrification rates by the less diverse urban microbial inoculum decreased in response to combined heavy metal and salt stress, while nonurban communities were unaffected. These findings support the hypothesis that higher diversity may confer greater functional resistance in response to multiple stressors and do not support the idea that stressful conditions select for communities that are functionally resilient to multiple stressors.
KeywordsDenitrification Disturbance Diversity Resistance Stress Urbanization
The authors thank B. Colman, B. Hassett, and S. Hayward for field and lab assistance. This research was supported by grants from the National Science Foundation NSF DEB 0546251 to ESB and NSF DEB 3320160 to SW and JPW.
- Anderson, M. J., 2001. A new method for non-parametric multivariate analysis of variance. Austral Ecology 26: 32–46.Google Scholar
- Blackwood, C. B., D. Hudleston, D. R. Zak & J. S. Buyer, 2007. Interpreting ecological diversity indices applied to terminal restriction fragment length polymorphism data: insights from simulated microbial communities. Applied and Environmental Microbiology 73: 5276–5283.PubMedCentralPubMedCrossRefGoogle Scholar
- Johansson, M., M. Pell & J. Stenstrom, 1998. Kinetics of substrate-induced respiration (SIR) and denitrification: applications to a soil amended with silver. Ambio 40: 40–44.Google Scholar
- Kaushal, S. S., P. M. Groffman, G. E. Likens, K. T. Belt, W. P. Stack, V. R. Kelly, L. E. Band & G. T. Fisher, 2005. Increased salinization of fresh water in the northeastern United States. Proceedings of the National Academy of Sciences of the United States of America 102: 13517–13520.PubMedCentralPubMedCrossRefGoogle Scholar
- Mulholland, P. J., A. M. Helton, G. C. Poole, R. O. Hall, S. K. Hamilton, B. J. Peterson, J. L. Tank, L. R. Ashkenas, L. W. Cooper, C. N. Dahm, W. K. Dodds, S. E. G. Findlay, S. V. Gregory, N. B. Grimm, S. L. Johnson, W. H. McDowell, J. L. Meyer, H. M. Valett, J. R. Webster, C. P. Arango, J. J. Beaulieu, M. J. Bernot, A. J. Burgin, C. L. Crenshaw, L. T. Johnson, B. R. Niederlehner, J. M. O’Brien, J. D. Potter, R. W. Sheibley, D. J. Sobota & S. M. Thomas, 2008. Stream denitrification across biomes and its response to anthropogenic nitrate loading. Nature 452(7184): 202–205.Google Scholar
- Oskanen, J., F. G. Blanchet, R. Kindt, et al., 2010. Vegan: community ecology package. R package version 1: 17.Google Scholar
- Rosenberg, D. & V. H. Resh (eds), 1993. Freshwater Biomonitoring and Benthic Macroinvertebrates. Chapman and Hall, New York.Google Scholar
- Tsuzuki, M., O. V. Moskvin, M. Kuribayashi, K. Sato, S. Retamal, M. Abo, J. Zeilstra-Ryalls & M. Gomelsky, 2011. Salt stress-induced changes in the transcriptome, compatible solutes, and membrane lipids in the facultatively phototrophic bacterium Rhodobacter sphaeroides. Applied and Environmental Microbiology 29: 397–407.Google Scholar
- Walsh, C. J., A. H. Roy, J. W. Feminella, P. D. Cottingham, P. M. Groffman & R. P. Morgan, 2005. The urban stream syndrome: current knowledge and the search for a cure. Journal of the North American Benthological Society 24: 706–723.Google Scholar