Why are some invasive plant species so successful in nutrient-impoverished habitats in south-western Australia: a perspective from their phosphorus-acquisition strategies

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 southwestern 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
supplies 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.