The impacts of nitrogen utilization and allocation strategies on photosynthesis for an invasive grass, Phalaris arundinacea, in comparison to the native sedge, Carex stricta.

Phalaris arundinacea (reed canary grass) is an invasive C3 perennial grass of temperate/boreal wetland communities. It is more abundant in areas with high nitrogen (N) inputs. Our hypothesis is P. arundinacea gains a competitive advantage over Carex stricta, the native sedge it often displaces, with increased N, because it allocates more N to features that enhance net carbon gain than C. stricta does. To test this hypothesis, we are comparing the responses of photosynthetic parameters and leaf morphology to various N levels (0.15 to 45 mM N) for P. arundinacea and C. stricta. We grow the plants in a course medium whose N content is controlled by varying the nitrate and ammonium in standard Hoagland’s solution. With an increase in the N concentration provided, we observed an increase in net CO2 assimilation on an area basis (A), leaf N content, leaf area, and specific leaf area (SLA) for P. arundinacea, but the effect on chlorophyll content was not clear. At low concentrations of N supplied C. stricta, had the higher A, leaf N content and leaf area compared to P. arundinacea. It appears that N level affects total carbon gain for P. arundinacea by affecting A, leaf area, and SLA, allowing it to rapidly attain its full height and shade C. stricta. These advantages of high nitrogen had made the P. arundinacea become more aggressive and invade the wetlands displacing the C. stricta.