Assessing soil bacterial community composition and structure across wetland, transition zone, and upland ecosystem types along a single transect in Macon County, Alabama

Background/Question/Methods . Wetlands provide essential functions to the ecosphere that range from water filtration to flood control.  These wetlands have also been reported to contain diverse assemblages of various organisms that greatly distinguish them from other ecosystems.  During the 20^th century about 53% of the nation’s original wetland acreage was destroyed as a result of agricultural and urban development.  Current methods of evaluating the quality of wetlands include assessing vegetation, soil type, and period of inundation.  Although these and other assessments have gained notoriety, some researchers have begun to question their efficacy in indicating ecological impact.  Identifying sensitive indicators of ecological change that allow for the distinction of the unique ecosystems has become an important area in soil ecology. With recent advances in molecular and bioinformatic techniques, measurement of the structure and composition of soil bacterial communities has become an alternative to traditional methods of ecological assessment.  The objective of the current study was to determine whether soil bacterial community composition and structure changed with respect to three ecosystem types (wetland, transition zone, and upland) along a single transect in Macon County, AL. Nine soil samples from each ecosystem type were extracted for DNA and checked using 0.8% agarose gel. Samples were then quantified using Nanodrop 1000 and composited into three samples per ecosystem type (to account for variation across sampling sites) prior to submission for pyrosequencing. The resulting sequences were assessed for phylogenetic and compositional differences using the open-source software, MOTHUR.

Results/Conclusions . As in previous studies, Proteobacteria were the most abundant phyla throughout the soils in the study (ranging from 42.1% to 49.9% of total sequences). The relative abundance of phyla Acidobacteria (37.4%) and Verrucomicrobia (7.0%) were highest in relative abundance in wetland soils, Actinobacteria (14.6%) was highest in the transition area, and Chloroflexi (1.6%) was highest in upland soils.  Double dendrograms and PCoA plots were generated, showing distinction amongst the ecosystem types through clustering by class abundance and Unifrac scores at 3% dissimilarity, respectively.  Selected soil properties (SOM and phosphatase enzyme activity) also differed significantly across ecosystem types, while showing predominance in the wetland area.  This study suggests that with further study the structure and composition of soil bacterial communities may eventually be an important indicator of ecological impact in wetland ecosystems.