Strategies in Ericaceae to acquire phosphorus in phosphorus‐impoverished habitats in the southwest Australian biodiversity hotspot

In the Southwest Australian Biodiversity Hotspot, the greatest plant species diversity tends to occur on the most phosphorus (P)‐impoverished soils. Many plant species in this P‐impoverished environment release root carboxylates that mobilise soil P which is a more effective mechanism than mycorrhizas in severely P‐impoverished habitats. For ericoid mycorrhizal Ericaceae, a prominent and diverse family in southwest Australia, it is unclear whether they release carboxylates as a P‐acquisition strategy. We hypothesised that some Ericaceae exhibit high leaf manganese (Mn) concentrations ([Mn]), a proxy for rhizosphere carboxylates and release root carboxylates. Since carboxylates not only mobilise P but also Mn, whose uptake is poorly controlled in plants, we used leaf [Mn] in the natural habitat as a proxy for rhizosphere carboxylate concentrations. We compared their leaf [Mn] with that of positive and negative reference species, known to release carboxylates or not, respectively. To follow up, we measured the carboxylate exudation rates of targeted species with high and low leaf [Mn] using seedlings grown in low‐P nutrient solutions. Using these complementary approaches, we confirmed that Ericaceae in P‐impoverished habitats with high leaf [Mn] exhibit a carboxylate‐releasing P‐mobilising strategy, like non‐mycorrhizal Proteaceae. Surprisingly, some species with low leaf [Mn], which occurred in habitats with high soil pH, also released carboxylates. Therefore, low leaf [Mn] cannot conclusively indicate the absence of carboxylate exudation. These species may release carboxylates along with cations such as potassium or magnesium, which increase the rhizosphere pH, thereby decreasing Mn availability and accumulation in mature leaves. The lack of a significant phylogenetic signal detected for leaf [P] and leaf [Mn] across sampled taxa indicated these nutrient acquisition traits are not only limited to certain clades but also likely evolved independently multiple times in Ericaceae. Styphelia sensu lato exhibited the widest trait variation (highest to lowest leaf [P] and [Mn]) of all genera included in this study. The high diversity and abundance of Ericaceae in southwest Australia may be associated with the presence of carboxylate release to mobilise P, making them successful in these severely P‐impoverished habitats without reliance on ericoid mycorrhizas alone. Read the free Plain Language Summary for this article on the Journal blog.