Master of Science (MSc)
Faculty of Science
Dr. Robin Slawson
Riparian zones are a type of wetland described as the interface between land and a body of water such as a river or stream. Riparian zones are effective buffers against anthropogenic pollutants and nutrient loads from non-point sources that can greatly diminish water quality. Riparian zones can host a variety of plant species and associated microbial communities. The combined biological processes of plants, bacteria, and arbuscular mycorrhizal fungi (AMF) are key to nutrient cycling and nutrient removal in riparian zones. As such, understanding the factors that influence them is critical for watershed management. This research is targeted at obtaining a better understanding of how changing effluent conditions affect rhizosphere bacterial community structure and function as well as the colonization rates of arbuscular mycorrhizal fungi. In lab-scale planted wetland mesocosms, established with different plant species (Phalaris arundinacea and Veronica anagallis-aquatica) and different water quality conditions (high and low quality), we assessed shifts in bacterial community structure and function as well as AMF colonization rates in response to changing effluent conditions. During phase 1 of the experiment, half of the mesocosms planted with Phalaris arundinacea and half of the mesocosms planted with Veronica anagallis-aquatica were randomly selected to receive either high or low quality water. After 91 days of receiving different water quality inputs, all mesocosms received a phosphorus addition. In response to a phosphorus addition, bacterial community structure (assessed using denaturing gradient gel electrophoresis) remained similar between all treatment groups (>50%), with the exception of one outlier at 35 days after exposure (DAE), for the duration of the experiment. Bacterial community function (assessed using Biolog Ecoplate™ data) was differentiated more often by water quality treatment than associated plant species. AMF colonization rates of both plants species in both water quality conditions were assessed using a multiple linear regression that considered plant species, water quality, and time (days after exposure) as main effects and also considered all 2 way interactions and one 3 way interaction. Arbuscular colonization rates were found to differ based on plant species (P=0.052) in response to the phosphorus addition with Phalaris arundinacea experiencing a decreasing trend or no significant change in AMF colonization and Veronica anagallis-aquatica experiencing an increasing trend in colonization. Forty-seven days after exposure to the phosphorus addition, mesocosm systems were switched to an artificial freshwater composition for 66 days to allow communities to adjust before receiving an artificial wastewater addition with no added organisms. Similar to the phosphorus exposure, bacterial community structure remained similar between all treatment groups (>65%) throughout the experiment. At 0 DAE, no consistent differences between plant species and water quality treatment groups were observed. Shifts in both bacterial community structure and function became homogenous in response to the artificial wastewater addition. All treatment group communities remained homogenous to varying degrees after 20 DAE. Due to difficulties in acquiring viable samples of Veronica anagallis-aquatica, analysis of AMF colonization was limited to the Phalaris arundinacea treatment groups. AMF colonization was not significantly different between water quality groups or over time in Phalaris arundinacea. Overall, the findings suggest shifts in rhizosphere bacterial community structure and function are linked to changes in inflow water conditions. Our findings also show that AMF colonization rates can differ between plant species and can be affected by a phosphorus addition after 47 DAE. Additionally, AMF colonization can change independently of the shifts occurring in rhizosphere bacterial communities. We have demonstrated that changes in the two microbial communities can be independent and that these communities display different sensitivities to different nutrient loads. Established riparian zone rhizosphere microbial communities were resilient to the effects of the nutrient loads we assessed. The shifts in community structural and functional profiles were temporary and communities were influenced by the same factors before nutrient loading as they were after.
Bannister, James, "Riparian Zone Soil Microbial Community Dynamics: Interactions with Nutrient Loadings" (2019). Theses and Dissertations (Comprehensive). 2165.