Effect of invasion and control of Phragmites australis on soil microbial community composition and abundance in Great Lakes coastal wetlands

Background/Question/Methods

Wetlands support a rich diversity of species but also perform important ecosystem services such as carbon and nutrient cycling, largely facilitated by microorganisms. Invasive plant species, such as the common reed, Phragmites australis, reduce plant diversity and alter plant-microbe interactions, yet the extent of the impact on microbial communities has not been well defined. To control Phragmites, a combination of the broad-spectrum herbicides glyphosate and imazapyr, are often applied. While the toxicity effect on macro-organisms and specific model microorganisms has been well researched, effects on microbial community composition and abundance within freshwater wetlands have not. We hypothesized that invasion of Phragmites would result in a shift in microbial community composition and abundance compared to wetlands with native-dominated vegetation while removal efforts employing herbicide and/or prescribed burn treatments would produce greater shifts. This was tested by collecting soils from freshwater coastal wetlands along Lake Erie adjacent to the Detroit River dominated by invasive Phragmites and native vegetation. Additionally, a series of soil samples were obtained prior to and following large-scale herbicide application. A genetic fingerprinting technique known as terminal restriction fragment length polymorphism was performed to characterize the microbial species composition, while quantitative PCR was used to assess microbial abundance.

Results/Conclusions

Soil microbial community composition differed by vegetation type within Phragmites-dominated versus native-dominated wetlands, as indicated by principal component analysis. Some inter-annual effects were evident in microbial community structure. Microbial diversity was generally greater in native-dominated vegetation, though only significant on one date (p < 0.05), whereas microbial abundance was greater under Phragmites-dominated vegetation and differed significantly later in the growing season (p < 0.05). Microbial community composition and diversity after herbicide application exhibited only small changes immediately after exposure while site location conferred greater differences in microbial structure. Our results suggest vegetation type greatly influences soil microbial community composition and abundance while herbicide application may have only relatively minor impacts.