Physiological traits to assess Hieracium pilosela L. invasion in the Magellanic steppe of Tierra del Fuego Island (Argentina)

DIAZ BARRADAS, MARI CRUZ; ZUNZUNEGUI, M.; ESQUIVIAS SEGURA, M.P.; ALVAREZ CANSINO, L.; COLLANTES, M.B.; CIPRIOTTI, P.A.

Lyon

Simposio; 54th International Association of Vegetation Science Symposium; 2011

IAVS

The invasion of natural ecosystems by alien species drives to a reduction of biodiversity and modifies ecosystem function. In addition, island ecosystems are particularly vulnerable to biological invasion because of the relative isolation from the mainland. The specific traits of an invading species and the interaction with abiotic factors and native community may determine the success of invasions. The herb Hieracium pilosella has invaded the northern Tierra del Fuego rangelands since 1990, approximately, forming in some cases large patches that replace native flora and decrease the quality of grasslands for sheep grazing. The main aim of this study was to investigate how H. pilosella is affecting leaf nutrient dynamics and carbon exchange characteristics of the dominant plant species in the Fuegian steppe; with this specific aim we are trying to assess how this species is a strong grassland invader in different parts of the world. Different traits have been compared among the invasive alien species and native species (Festuca gracillima, Poa spiciformis and Acaena pinnatifida) and a non-invasive alien species (Trifolium repens). Field gas exchange, photochemical efficiency, relative water content, laboratory measurements (proline and chlorophyll content), and nutrient concentration and stable isotope composition have been measured in the above species with and without interaction H. pilosella and in the invasive species between the centre and border of patches. Results show that all native species suffered a significant increase in N signature when are invaded by H.pilosella, probably due to its higher decomposition rate, although a negative relationship was found between N and nitrogen content. Proline content was significant higher in leaves of some non-invaded species and was negatively correlated with C/N ratio. Δ13C exhibited the highest values in F. gracillima and was negatively correlated with intrinsic A/gs, hence could be used as a long term proxy of WUE. F. gracillima the tallest species of this community suffered a significant decrease of Δ13C when it grows with the invasive species, while H. pilosella exhibited a significant increase. This results enhanced the effects of inter and intraspecific competition in water economy in an area subjected to strong winds.Although the effects of the competition with the invasive species were small compared to the differences among species, the results of MANOVA and Canonical Discriminant Analysis showed significant overall differences between natural and invaded grasslands, which supports the hypothesis that H. pilosella is modifying plant traits in the community