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Buenos Aires, Argentina

Diaz-Barradas M.C.,University of Seville | Zunzunegui M.,University of Seville | Alvarez-Cansino L.,University of Bayreuth | Esquivias M.P.,University of Seville | And 2 more authors.
Plant and Soil | Year: 2015

Aims: The principal objective was to evaluate the interference by the invasive species, H. pilosella, on native grassland species at the physiological performance level. We hypothesised that the invasive species is able to alter the nitrogen uptake of native plant species, and can modify community functioning. Methods: This study was performed under field conditions in the Magellanic Steppe (Argentina). We compared stable isotope signatures, nutrient content and several functional physiological traits in four grassland species with and without H. pilosella interference. Results: We found significant interference effects from the invasive species on native species, mostly through changes in nitrogen uptake. The variation in the natural abundance of foliar δ15N suggests that the native plants switched nitrogen sources due to interference with the exotic species. A linear relationship between chlorophyll and proline content that disappears when species are under H. pilosella interference, suggests major changes in the N allocation of native species. Grassland species under interference with exotic species exhibit lower photochemical efficiency and higher water use efficiency. Canonical discriminant analysis evidenced the existence of a different set of functional traits between invasive and native plants, and also among native species with and without H. pilosella interference. Conclusions: Our results support the hypothesis that H. pilosella exerts intense interference with native species through shifting the N sources available for native species, a lower leaf N content, and increasing water stress. © 2015, Springer International Publishing Switzerland.

Diaz-Barradas M.C.,University of Seville | Zunzunegui M.,University of Seville | Collantes M.,Laboratorio Of Ecologia Of Pastizales | Alvarez-Cansino L.,University of Bayreuth | Garcia Novo F.,University of Seville
Acta Oecologica | Year: 2014

Following the theory on costs of reproduction, sexually dimorphic plants may exhibit several trade-offs in energy and resources that can determine gender dimorphism in morphological or physiological traits, especially during the reproductive period. In this study we assess whether the sexes of the dioecious species Empetrum rubrum differ in morphological and ecophysiological traits related to water economy and photochemical efficiency and whether these differences change in nearby populations with contrasting plant communities.We conducted physiological, morphological, sex ratio, and cover measurements in E rubrum plants in the Magellanic steppe, North-Eastern part of Tierra del Fuego (Argentina), from two types of heathlands with differing community composition.We found differences between sites in soil pH and wind speed at the canopy level. E. rubrum plants exhibited lower photosynthetic height and higher LAI (leaf area index), lower RWC (relative water content) and higher water-use efficiency (lower δ13C) in the heathland with harsher environmental conditions. Gender dimorphism in the physiological response was patent for photochemical efficiency and water use (RWC and δ13C discrimination), with males showing a more conservative strategy in relation to females. Accordingly, male-biased sex ratio in the stress-prone community suggested a better performance of male plants under stressful environmental conditions. The integrated analysis of all variables (photochemical efficiency, RWC, leaf dry matter content (LDMC), pigments, and δ13C) indicated an interaction between gender and heathland community effects in the physiological response. We suggest that female plants may exhibit compensatory mechanisms to face their higher reproductive costs. © 2014 Elsevier Masson SAS.

Rauber R.B.,Laboratorio Of Ecologia Of Pastizales | Rauber R.B.,Instituto Nacional de Tecnologia Agropecuaria | Collantes M.B.,Laboratorio Of Ecologia Of Pastizales | Cipriotti P.A.,Laboratorio Of Ecologia Of Pastizales | And 2 more authors.
Austral Ecology | Year: 2013

The biotic resistance theory relates invader success to species richness, and predicts that, as species richness increases, invasibility decreases. The relationship between invader success and richness, however, seems to be positive at large scales of analysis, determined by abiotic constraints, and it is to be expected that it is negative at small scales, because of biotic interactions. Moreover, the negative relationship at small scales would be stronger within species of the same functional group, because of having similar resource exploitation mechanisms. We studied the relationship between the cover of a worldwide invader of grasslands, Hieracium pilosella L., and species richness, species diversity and the cover of different growth forms at two different levels of analysis in 128 sites during the initial invasion process in the Fuegian steppe, Southern Patagonia, Argentina. At regional level, the invader was positively correlated to total (r=0.28, P=0.003), exotic (r=0.273, P=0.004), and native species richness (r=0.210, P=0.026), and to species diversity (r=0.193, P=0.041). At community level, we found only a weak negative correlation between H. pilosella and total richness (r=-0.426, P=0.079) and diversity (r=-0.658, P=0.063). The relationship between the invader and other species of the same growth form was positive both at regional (r=0.484, P<0.001) and community (r=0.593, P=0.012) levels. Consequently, in the period of establishment and initial expansion of this exotic species, our results support the idea that invader success is related to abiotic factors at large scales of analysis. Also, we observed a possible sign of biotic constraint at community level, although this was not related to the abundance of species of the same growth form. © 2012 The Authors. Austral Ecology © 2012 Ecological Society of Australia.

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