Differences in wetland plant community establishment with additions of nitrate-n and invasive species (phalaris arundinacea and typha xglauca)

Restored prairie pothole wetlands in North America are often enriched by nitrate-N (NO3-N) that has been lost from surrounding agricultural systems. In addition, these wetlands are increasingly colonized by invasive taxa including Phalaris arundinacea L. and Typha xglauca Godr. To explore the impacts of NO3-N enrichment, suppression by invasive species, and the interaction of these factors on restored communities, we grew native sedge meadow communities from seed in greenhouse mesocosms and subjected them to NO3-N and invasive species for 4 months. Typha xglauca did not reduce overall native community biomass and actually enhanced Aster spp. biomass. Phalaris arundinacea suppressed growth of the native community to an equal relative extent across all NO3-N levels. The shoot biomass of the entire native community in untreated plots was similar to the P. arundinacea fraction of the treated plots. Phalaris arundinacea demonstrated greater plasticity in root-shoot allocation than the native community over the range of NO3-N inputs. Proportional allocation to root biomass was greater for R arundinacea than for the native community at all but the highest NO3-N level. Both factors may be important in explaining dominance of P. arundinacea over the native community in a range of fertility conditions. Regardless of NO3-N inputs, the restoration of diverse native wetlands requires strict control of P. arundinacea during community establishment, as evidenced by the relatively rapid rate of suppression of native community biomass by P. arundinacea compared with T. xglauca.