Reed canary grass (Phalaris arundinacea L.) is an invasive, cool-season grass commonly dominating wetlands with high nutrient loads. Its impact on nitrogen removal via denitrification in wetlands is unknown. Most studies of denitrification in treatment wetlands have focused on the effects of physical or chemical variables and not on the effects of plant roots on the soil environment. The purpose of this study was to measure effects of plant type on denitrification rates in typical wetland soils of the midwestern United States by comparing wet prairie mix, switchgrass-dominated, and reed canary grass plant communities. Nitrate (NO3 −) removal and other parameters were measured in miniature wetlands, or mesocosms, containing each plant community transplanted from a small agricultural treatment wetland in southern Minnesota. Quantitative polymerase chain reaction analysis was used to quantify the total bacteria population (measured with 16S rRNA genes) and denitrifying gene abundance (measured with nosZ genes) from the rhizosphere of each plant community. The wet prairie mix mesocosms on average removed the most NO3 − in each test (p =.01 and.08). Whereas the wet prairie mix removed the most NO3 − from the surface water (p <.01), reed canary grass removed more from the subsurface (p <.01). Ratios of denitrifying to total bacteria were higher in the wet prairie mix than in the other communities’ root zones (p <.05). Results suggest that reed canary grass invasion could reduce denitrification in wetlands, especially during the spring and fall when it is growing but other plants are dormant.
Bibliographical noteFunding Information:
This study was supported in part by a grant from the Minnesota Department of Agriculture through the Clean Water Legacy Fund. This study was one chapter of a PhD dissertation in Water Resources Science at the University of Minnesota, St. Paul, MN. The Department of Biopoducts and Biosystems Engineering provided some support for equipment and undergraduate hours. Numerous undergraduate and graduate students assisted in the setup and monitoring of the mesocosms. The LaPara Research Group in the University of Minnesota Department of Civil, Environmental, and Geo-Engineering provided partial funding for the qPCR analysis, and students from the research group assisted with the analysis.
© 2020 The Authors. Journal of Environmental Quality © 2020 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
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