Facilitation and competition between Acacia species and phosphorus‐mobilising plants in severely phosphorus‐impoverished habitats

Plants in fire‐prone severely phosphorus (P)‐impoverished environments exhibit diverse P‐acquisition strategies coordinated with root morphological traits. Fire transiently enhances plant‐available soil P, making efficient post‐fire P acquisition crucial for seedling survival of post‐fire seeder perennials as soil P availability declines over time. However, whether post‐fire seeder perennials express a diversity of P‐acquisition strategies across three stages of seedlings after a fire and how their root morphological traits are coordinated, remains unknown. For Acacia pulchella and Acacia lasiocarpa (Fabaceae), two post‐fire seeder perennials native to southwest Australian P‐impoverished habitats, we investigated biomass, rhizosheath monophosphatase activity and carboxylate concentrations, represented by leaf manganese concentrations ([Mn]), leaf P‐resorption efficiency and root morphological traits. Seedlings were harvested at three stages in monoculture and mixture with P‐mobilising Banksia species (Proteaceae), under treatments with or without P addition to simulate soil P concentrations ([P]) immediately and many years post‐fire, respectively. The two species of Acacia exhibited distinct P‐acquisition strategies. A. pulchella initially relied on increased soil P availability and subsequently its P acquisition was facilitated by Banksia attenuata ( B. attenuata ), while consistently depending on releasing monophosphatases. Conversely, A. lasiocarpa relied on releasing carboxylates and monophosphatases to mobilise and acquire P, even at elevated soil [P]. There were efficiency interactions among root morphological traits, rhizosheath monophosphatases, leaf [Mn] and leaf P‐resorption efficiency. For both Acacia species, total biomass was most strongly predicted by root morphological traits. We conclude that traits related to the acquisition of soil P, such as root morphological characteristics, rhizosheath monophosphatases and leaf [Mn] were more evident in supporting plant growth in severely P‐impoverished ecosystems than traits associated with internal P conservation, such as leaf P‐resorption efficiency. These two types of traits interacted and functioned synergistically, enhancing total plant biomass. Read the free Plain Language Summary for this article on the Journal blog.