Soil-dependent growth strategy of invasive plants: empirical evidence and model predictions using Carpobrotus edulis as target species

Plants experience different soil conditions that may influence several aspects of their biology such as nutrient uptake, root competition, growth and even floral display (Mal & LovettDoust 2005). For clonal plants, the relative investment in sexual reproduction or vegetative growth can vary according to the context in which they grow (e.g. invaded soil vs. noninvaded) since environmental constrains may result in contrasting dispersal strategies due to differential cost-benefit balances (Kot et al., 1996). Carpobrotus edulis (L.) N. E. Br., is considered a highly invasive species in coastal areas of Southern Europe because it forms dense fast-growing mats that displace the native dune vegetation (Vila et al., 2006). Carpobrotus edulis can change drastically the characteristics of the invaded soil and the longterm occurrence of the species has been associated with a decrease in pH and increase in organic content (Conser in press; D'Antonio & Mahall, 1991). Nevertheless, and in spite of the large dense patches of C. edulis formed in invaded areas, there is no information available about how these changes in soil may affect the posterior growth and colonization rate of the species. The objective of the present study was to evaluate whether the residual effects on soil after C. edulis invasion affect the growth plasticity of the species and to model the long-term consequences of such growth responses. Our working hypothesis was that soil modification introduced by C. edulis leads to plant growth responses oriented to maximize the colonization rate of invaded areas.