Why are some invasive plant species so successful in nutrient‐impoverished habitats in south‐western Australia: A perspective based on their phosphorus‐acquisition strategies

Abstract Invasive plants are a major cause of the global biodiversity crisis; it is therefore crucial to understand mechanisms that contribute to their success. South‐western Australia is a global biodiversity hotspot with extremely low soil phosphorus (P) concentrations. In this region, a large proportion of native plant species release carboxylates that mobilise soil P. Many widespread invasive plant species in south‐western Australia are arbuscular mycorrhizal (AM). We hypothesised that some of these invasive AM plant species exhibit similar P‐acquisition strategies as native carboxylate‐releasing P‐mobilising species which allows them to thrive in P‐impoverished soils. To test this hypothesis, we collected 23 common invasive species in the field and assessed their leaf manganese concentration [Mn], relative to that of native reference species at different locations, as a proxy for carboxylate release. In addition, we cultivated seven of the invasive species in hydroponics at different P supply to measure their root carboxylate exudation. Furthermore, we measured leaf P concentration and photosynthetic P‐use efficiency (PPUE) of five invasive species in the glasshouse. In the field investigation, almost all invasive species exhibited significantly higher leaf [Mn] than the negative references, which do not release carboxylates, indicating carboxylate release of the invasive plants. Leaf [Mn] of a few invasives even exceeded that of positive references, which exhibit significant carboxylate release, indicating substantial carboxylate release of these invasives. All glasshouse‐grown invasive species with high field leaf [Mn] released root carboxylates under low P supply. Most of the tested invasive plant species also exhibited greater PPUE than native plants under low P supply. Invasive AM plant species exhibited root exudation of carboxylates as a P‐acquisition strategy, which very likely allows their successful invasion of severely P‐impoverished habitats. Read the free Plain Language Summary for this article on the Journal blog.