Invasion legacies of Carpobrotus edulis negatively affect the endangered Iberodes littoralis subsp. gallaecica

The invasive South African plant Carpobrotus edulis threatens biodiversity and disrupts coastal ecosystems, yet the effects of soil legacies on the life cycle of native plants remain poorly understood. Here, we assessed whether a short-term invasion by C. edulis induces soil changes that remain after removal and affect the performance of the endangered dune plant Iberodes littoralis subsp. gallaecica across its life cycle. In 16 experimental plots (eight previously invaded and eight non-invaded), we characterised soil properties at two depths and sowed seeds from five I. littoralis populations to assess germination, survival to flowering, flowering phenology, flower number, leaf reflectance, biomass traits and reproductive output. Previously invaded plots showed reductions in NH₄ ⁺-N, total N, Cu and Zn, and increases in δ¹³C, P and Al, while invasion effects on NO₃ ^--N and pH varied with soil depth, as did soil-plant relationships. Soil legacies promoted germination in I. littoralis but reduced survival to flowering, flowering duration, growth and reproductive investment, ultimately resulting in lower seed production. Despite phenotypic differences among provenances, intra-specific variation did not mitigate the adverse effects of soil legacies on plant performance. Our findings show that just 14 months of C. edulis invasion can leave soil legacies in nutrient availability and soil chemistry, with functional consequences for I. littoralis across its full life cycle. These results highlight the importance of considering legacy effects of invasion beyond early life stages of native plants and accounting for depth-related variation in soil properties and soil-plant relationships in restoration planning.