Metabolic Adaptations of the Non‐Mycotrophic Proteaceae to Soils with Low Phosphorus Availability

AbstractProteaceae are almost all non‐mycorrhizal and most species produce proteoid (= cluster) roots when grown in low‐phosphorus (P) soils. In south‐western Australia and the Cape Floristic Region of South Africa, Proteaceae have diversified more than anywhere else, and occur on the most severely P‐impoverished soils in the landscape. Several traits related to their P nutrition account for the success of south‐western Australian Proteaceae on P‐impoverished soils: (i) a P‐acquisition strategy based on carboxylate release from ephemeral cluster roots, which allows the species to ‘mine’ P that is ‘sorbed’ to soil particles; (ii) efficient use of P in photosynthesis, based on a very low investment in ribosomal RNA, extensive replacement of phospholipids by lipids that do not contain P, and allocation of P to photosynthetic cells and not epidermal cells; (iii) a very high P‐remobilisation efficiency; and (iv) a high seed P content. Proteaceae in southern South America do have a P‐acquisition strategy based on carboxylate release, but lack the other P‐efficiency traits. They occur on soils that contain vast amounts of P, but with a very low P availability, and invest less biomass in cluster roots. However, these ephemeral structures live somewhat longer and release far more carboxylates when compared with Proteaceae from south‐western Australia. The various aspects of P nutrition in Proteaceae across the world are discussed in a phylogenetic context.