Effects of the invasive herb Hieracium pilosella on the physiological performance of grassland native species in Tierra del Fuego.

DÍAZ- BARRADAS, M.C.; ALVAREZ-CANSINO, L.; ZUNZUNEGUI, M.; ESQUIVIAS, P.; CIPRIOTTI P.; COLLANTES M.

Oporto, Portugal

Congreso; World Conference on Biological Invasions and Ecosystems functioning; 2009

Exotic species introduction in ecosystems can lead to the alteration of microclimatic conditions and soil nutrient balance, consequently altering native communities’ diversity and dynamic. Hieracium pillosela (Asteraceae) is a western European herb, with high vegetative propagation capacity. The species is currently spreading on the Magallanic stepe, where it is replacing the native pasture species of Tierra del Fuego. To test the effect of H. pilosella on functional aspects of Tierra del Fuego’s pasture species, the physiological response of three native species (Festuca gracillima, Acaena pinnatifida, and Poa spiciformis) and one naturalized species (Trifolium repens) was analysed under competition and under non-invaded conditions. Measurements of chlorophyll fluorescence, leaf gas exchange, leaf nitrogen and proline content, and carbon and nitrogen isotope discrimination analysis were conducted. Results suggest different functional responses on native pasture species, with negative effects of competition with H. pillosella, mainly constraining water and light availability. Nevertheless, positive effects of the invasion were found in proline content that might be explained to a decrease in herbivory pressure.