The influence of light availability on competition between Phalaris arundinacea and a native wetland sedge

Invasions by Phalaris arundinacea (reed canarygrass) preclude establishment of sedge meadow vegetation in restored wetlands in the midwest USA. To evaluate cover crops as a potential method of P. arundinacea control, we examined the effects of lowering light availability (from 600 to 200 and 10 μmol m^-2 s^-1) on competition between P. arundinacea and a common wetland sedge, Carex hystericina (porcupine sedge), in a greenhouse experiment. Lowering light availability substantially reduced P. arundinacea total biomass, by 52% at 200 μmol m^-2 s^-1 and by 99% at 10 μmol m^-2 s^-1. However, shade also reduced C. hystericina total biomass, by 62% at 200 μmol m^-2 s^-1 and by 99% at 10 μmol m^-2 s^-1. Further, shade did not favor C. hystericina in competition with P. arundinacea. Instead, C. hystericina biomass was reduced significantly more by competition with P. arundinacea in partial shade than in full sun (by 69% compared to 58%), while P. arundinacea biomass was reduced significantly less by competition with C. hystericina in partial shade than in full sun (by 42% compared to 66%). Lowering light availability with a cover crop in restored prairie pothole wetlands might slow P. arundinacea invasion, but is unlikely to improve sedge meadow establishment.