Effects of Phragmites australis (Common Reed) Invasion on Nitrogen Cycling, Porewater Chemistry and Vegetation Structure in a Brackish Tidal Marsh of the Rhode River, Maryland

Abstract

Phragmites australis is one of the most widespread invasive species in wetland habitats of North America. Conversion of existing wetland ecosystems to Phragmites-dominated communities decreases overall plant diversity and alters biogeochemical cycles, which can negatively affect ecosystem processes. Previous studies demonstrated that Phragmites has a significantly greater above-ground nitrogen demand than native plants, likely due to its greater biomass. To evaluate how invasion by Phragmites alters standing stock nitrogen, I measured above- and below-ground biomass and nitrogen stocks in both the invasive and native plant communities to examine how Phragmites is meeting its documented increased nitrogen demand in the Rhode River, a sub-estuary of the Chesapeake Bay in Edgewater, Maryland. I also quantified deep N uptake using a 15N tracer study. I found that Phragmites roots significantly deeper than native marsh grass communities and has the ability to utilize deeper nitrogen pools and take up nitrogen from deeper depths. This enhanced rooting structure gives the invasive Phragmites the ability to potentially access lower salinity water, as well as tap nutrients unavailable to native marsh plant communities.