The effect of nutrients on seedling growth of native and introduced Phragmites australis

Differing responses to abiotic stresses and increased nutrient availability may play a role in the invasion and spread of introduced Phragmites australis Cav. (Trin.) ex. Steud. and the decline of native P.a. americanus Saltonstall, P.M. Peterson & Soreng in North America. We present results from an outdoor experiment where native and introduced P. australis seedlings were grown under two nutrient treatments. Both subspecies responded positively to increased nutrients but introduced plants clearly outperformed natives, growing taller, producing more stems, and had three to four times higher biomass. The biomass of introduced P. australis growing in low nutrients was similar to that of the native in high nutrients. Aboveground:belowground biomass ratios were nearly 1.25 for both native and introduced plants across treatments and reflect the high investment P. australis seedlings place on shoot production in their first year of growth. Our results also demonstrate that introduced P. australis can have explosive growth over a single growing season, even when established from seed. This implies that management of young, newly established populations may be prudent where introduced P. australis is considered undesirable, irregardless of whether eutrophication is an issue.