COMPETITIVE INTERACTIONS BETWEEN THE INVASIVE Symphyotrichum lanceolatum (Willd.) G. L. Nesom AND NATIVE Achillea millefolium L.

This study set out to explore the influence of reduced N concentration and competition on vegetative growth and resource allocation of Symphyotrichum lanceolatum (Willd.) G. L. Nesom and Achillea millefolium L. Comparison of two different genera from the family Compositae will allow the assessment of the impact of morphological or physiological constraints on resource allocation in species occupying the same habitat. Plants were grown in hydroculture. Culture types included two monoculture (invasive S. lanceolatum and native A. millefolium) and mixed culture (combination of those two species). Basic morphological and growth parameters from different treatments (reduced N concentration and control) were detel mined. Dry aboveground and below -ground biomass were measured, as well as the N concentration in leaves and P and K concentration in the above -ground and below ground biomass. The results showed that S. lanceolatum and A. millefolium produce approximately equal above -ground biomass, while S. lanceolatum produces significantly higher below -ground biomass. Further, the study suggests that S. lanceolatum tolerates a lower nitrogen concentration and that it out competes A. millefolium. This S. lanceolatum growth strategy could contribute to its spread since it allocates biomass to below -ground biomass at the beginning of its ontogenetic development, and thus creates the potential for greater resource acquisition.