Faculty Publication: Associate Professor of Biology Thomas Mozdzer

April 21, 2023

Mining of Deep Nitrogen Facilitates Phragmites australis Invasion in Coastal Saltmarshes

Authors: Mozdzer, Thomas J.; Meschter, Justin; Baldwin, Andrew H.; Caplan, Joshua S.; Megonigal, J. Patrick

Source: Estuaries and Coasts, DOI: 10.1007/s12237-022-01146-x, April 2023

Type of Publication: Article

Abstract: Phragmites australis (or common reed), one of the most widespread invasive species in wetlands of North America, has a high nitrogen (N) demand compared to native species. However, it is unclear how P. australis is able to meet this N demand, especially in systems with low soil N and limited N inputs. We evaluated whether deep rooting could be a mechanism by which P. australis accesses otherwise unused N pools, allowing it to circumvent nutrient competition and acquire the “missing N” needed to meet its N demand. We examined above and belowground N pools, as well as depth profiles of belowground biomass (to 3 m), in native and P. australis-dominated plant communities in two brackish marshes of the Chesapeake Bay. To evaluate whether deep roots contribute to P. australis meeting its high N demand, we amended soil porewater with 15N at four soil depths (10, 20, 40, and 80 cm) and measured the rate of 15N assimilation into plant biomass. We found that P. australis had 6–8 × the aboveground standing stock N, 2–3 × the total belowground biomass, and roots up to 3 × deeper than native plant communities (some exceeding 3 m). Our 15N tracer study demonstrated that P. australis acquired N from all measured soil depths, whereas N uptake by native plants was minimal below 20 cm. Our results demonstrate that deep rooting is a mechanism by which P. australis can access previously buried N pools, helping to satisfy its high N demand and thus fuel its invasion. Moreover, these results fundamentally challenge our understanding of biogeochemical processes deep within the soil profile given the presence of active roots at depths where they were previously thought to be largely inert.

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