Planktonic Bacterial Responses to Nutrient Amendments in Wetland Mesocosms

Although bacteria are important in the processing of anthropogenic nutrient inputs to wetlands, the effects of nutrient type and stoichiometry on bacterial communities have rarely been studied in natural systems. In this study, mesocosm enclosures were constructed in wetland pools at the Herrick Aquatic Ecology Research Facility at Kent State University (Kent, OH, USA) and amended with nutrients. Several experiments were conducted using various inorganic and organic nutrient sources (nitrate, ammonium, amino acids, phosphate, glucose-6-phosphate) as well as low, medium, and high N:P molar ratios. Structure of planktonic bacterial communities was determined using fluorescent in situ hybridization and denaturing gradient gel electrophoresis (DGGE) targeting Domain Bacteria and beta-proteobacteria. Abundances of Domain Bacteria, as well as other taxa examined (alpha-, beta-, and gamma-proteobacteria and the Cytophaga-Flavobacteria cluster), did not change in response to N:P ratios or nutrient amendments. However, Domain Bacteria, alpha-proteobacteria, and Cytophaga-Flavobacteria abundances varied among dates. DGGE clusters also contained communities collected on the same date, suggesting that temporal changes rather than nutrient amendments were the most important factor determining community composition. Overall, although some community changes appeared to be related to the nutrient amendments, temporal factors were a more important mediator of community structure.