Does Wet Prairie Vegetation Retain More Nitrogen with or withoutPhalaris arundinaceainvasion?

Abstract

Elevated nitrogen (N) levels accelerate expansion of Phalaris arundinacea L. (reed canary grass), a highly aggressive invader that displaces native vegetation and forms monotypes. Hence, Phalaris is commonly presumed to have high nutrient uptake that contributes to higher N retention in a wetland. We compared the capability of wet prairie vegetation with and without invading Phalaris under low-N and high-N treatments to (1) accumulate N in plant tissues, (2) retain N in soil and (3) remove N from water flowing through mesocosms. With high-N treatment, above-ground biomass increased by > 90% (P 46% (P = 0.0005; yrs. 1–2). Consequently, there was ~3 times as much total N accumulation in above-ground tissue (calculated from biomass and percent total N in tissues) with high-N treatment vs. low-N treatment (P 0.05) or in concentrations of NH4–N or NO3–N released in the discharged water (P > 0.1) from wet prairie mesocosms with and without invading Phalaris. Soil NH4–N did not differ between the wet prairie mesocosms with and without Phalaris invasions on five dates (P > 0.05); the one exception was in August 2004 (27% greater with invasion; P = 0.02). Our results from wet prairie mesocosms do not support the presumption that Phalaris retains more N than native plant assemblages.