Habitat Specialization Along a Wetland Moisture Gradient Differs Between Ammonia-oxidizing and Denitrifying Microorganisms
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Gradients in abiotic parameters, such as soil moisture, can strongly influence microbial community structure and function. Denitrifying and ammonia-oxidizing microorganisms, in particular, have contrasting physiological responses to abiotic factors such as oxygen concentration and soil moisture. Identifying abiotic factors that govern the composition and activity of denitrifying and ammonia-oxidizing communities is critical for understanding the nitrogen cycle. The objectives of this study were to (i) examine denitrifier and archaeal ammonia oxidizer community composition and (ii) assess the taxa occurring within each functional group related to soil conditions along an environmental gradient. Soil was sampled across four transects at four locations along a dry to saturated environmental gradient at a restored wetland. Soil pH and soil organic matter content increased from dry to saturated plots. Composition of soil denitrifier and ammonia oxidizer functional groups was assessed by terminal restriction fragment length polymorphism (T-RFLP) community analysis, and local soil factors were also characterized. Microbial community composition of denitrifiers and ammonia oxidizers differed along the moisture gradient (denitrifier: ANOSIM R = 0.739, P < 0.001; ammonia oxidizers: ANOSIM R = 0.760, P < 0.001). Individual denitrifier taxa were observed over a larger range of moisture levels than individual archaeal ammonia oxidizer taxa (Wilcoxon rank sum, W = 2413, P value = 0.0002). Together, our data suggest that variation in environmental tolerance of microbial taxa have potential to influence nitrogen cycling in terrestrial ecosystems.
KeywordsDenitrification Environmental Gradient Terminal Restriction Fragment Length Polymorphism Cetyl Trimethyl Ammonium Bromide Microbial Community Composition
We would like to thank M. Lemke, S. McClure, T. Hobson, and D. Blodgett for logistical assistance in the field. Emiquon Preserve is being restored by The Nature Conservancy. S. Paver, D. Nelson, J. Tsai, and R. Darmody provided technical assistance in the laboratory and R. Lankau and E. Wheeler for statistical assistance. S. Paver, O. Sinno and R. Andrus assisted in the field. Y. Cao, J. Dalling, M. Wander, K. Amato, S. Paver, C. Allsup, D. Keymer, E. Wheeler, A. Yannarell, and two anonymous reviewers contributed helpful comments to earlier versions of this manuscript. This work was supported by the Cooperative State Research, Education and Extension Service, U.S. Department of Agriculture, under project number ILLU 875-374. This research was also supported, in part, by the Program in Ecology, Evolution, and Conservation Biology at the University of Illinois at Urbana–Champaign.
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