Zur Plastizität des Reproduktiven Aufwandes bei Conyza Canadensis und Tanacetum Vulgare

Abstract

Plasticity of reproduction in Conyza canadensis and Tanacetum vulgare. — The reproductive effort of the annual Conyza canadensis and the perennial Tanacetum vulgare were compared under different watering treatments. Both species are common on urban waste-land, but optimal abundance is achieved under different frequencies of disturbance. The hypothesis that the annual ruderal flowers even under severe stress while under the same conditions the perennial gives priority to vegetative propagation was tested. Allocation of biomass to the reproductive organs of the annual Conyza canadensis was considerably higher than in the perennial Tanacetum vulgare. Additional water stress reduced the reproductive effort of Conyza canadensis, but the mean seed production was still more than 30’000 seeds per individual. In Tanacetum vulgare however, identical stress completely inhibited reproductive effort. In contrast, Tanacetum vulgare maintained vegetative propagation by means of rhizome production even under severe water stress. The adaptative value of these different strategies is discussed in relation to habitat dynamics.