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Non-Native Marsh Grass (Phragmites australis) Enhances Both Storm and Ambient Nitrogen Removal Capacity in Marine Systems


Marshes play a key role in global nitrogen cycling at the land–water margin. Invasive species are generally considered detrimental as they alter ecosystems they invade, but recent studies have shown some established invasive species can enhance certain ecosystem functions. The European haplotype of Phragmites australis is an aggressive and widespread invasive plant species in North America. We hypothesized that P. australis may play an important role in marsh nitrogen cycling by promoting higher rates of sediment denitrification compared with native marsh species. Seasonal measurements of sediment dissolved gas (N2 and O2) fluxes at three sites within the Albemarle-Pamlico Region of North Carolina compared sediments from invasive P. australis, native Spartina alterniflora, and/or Juncus roemarianus, and unvegetated sediments. In a marine tidal site, annual net denitrification in sediments associated with upland P. australis was highest compared to lower elevation marsh species or unvegetated sediments under ambient (139 μmol N2-N m−2 h−1) and nitrate enriched (219 μmol N2-N m−2 h−1) conditions. N2 fluxes were lower in sediments from two brackish marshes and did not differ between associated species, unvegetated sediments, or between high or low organic matter sites. Treatments with elevated nitrate showed enhanced net denitrification in most sediments at the marine site, suggesting the capacity to remove additional nitrate delivered episodically. Additionally, N2 fluxes measured before and after Hurricane Florence showed an increase in denitrification in P. australis sediments after the hurricane. Ecosystem value for this nitrogen removal service in the marine tidal site was estimated at US$ 266–426 *ha−1*yr−1. These results demonstrate an important role for invasive P. australis in coastal nitrogen cycling in marine environments and provide landscape context for potential biogeochemical impacts of this invasion.

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This research was supported by funding from the North Carolina Sea Grant and the Albemarle Pamlico National Estuary Partnership (project R/MG-1711). We thank the following members of the Piehler Lab at the UNC Institute of Marine Sciences for field and laboratory assistance: O. Torano, A. Gold, P. Mullin, J. Gould, L. Arroyo and C. Brown. The authors would also like to thank C. Currin and three anonymous reviewers for their insightful comments that significantly enhanced this paper.

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Correspondence to Mollie R. Yacano.

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Communicated by R. Scott Warren

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Schematic of sampling design (EPS 608 KB)

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Yacano, M.R., Thompson, S.P. & Piehler, M.F. Non-Native Marsh Grass (Phragmites australis) Enhances Both Storm and Ambient Nitrogen Removal Capacity in Marine Systems. Estuaries and Coasts 45, 2012–2025 (2022).

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