Is richer always better? Consequences of invaded N-rich soils for the early growth of a native and an invasive species

Abstract

Despite growing evidence that many invasive plants have impacts at soil level, it is less clear how these changes affect the recovery of invaded systems after their removal. Acacia longifolia is an invasive species in coastal areas around the world; it modifies soil properties and forms a thick layer of litter that can hinder the recovery of native dune communities and facilitate its own invasion. Ammophila arenaria is a key native species in the Portuguese foredunes but its habitat is gradually invaded by A. longifolia. Aiming to assess the influence of the soil altered by A. longifolia invasion on the germination and early growth of A. arenaria and A. longifolia, seeds of both species were sown under controlled conditions in native and invaded soils, and in the presence or absence of A. longifolia litter. Considering our main goal (to assess the development of each species in different conditions), and because study species have different growth forms, species were treated separately. Both species germinated better in the native soil, but after 12 weeks A. arenaria and A. longifolia had better performance in the invaded soil, exhibiting longer shoots, and higher biomass, leaf area, and relative growth rate. The root mass fraction was higher in the native soil. The added litter had no significant effect on germination or growth of either species. These results suggest that after the removal of A. longifolia no special measures are necessary to restore foredunes soil when promoting A. arenaria populations, although such measures could delay the growth of A. longifolia. Our results emphasize the importance of managing biological invasions at early stages as restoration is easier and prevent positive feedbacks that further promote the invasive species. However, more studies are needed to understand when management measures at soil level are required in ecological restoration projects.