Pasteurisation of soil from an extremely phosphorus-impoverished habitat increases phosphorus availability and enhances the growth of Agonis flexuosa (Myrtaceae)

Abstract Background and aims Soil pasteurisation will unavoidably affect soil abiotic properties. Such changes are often overlooked in extremely phosphorus (P)-impoverished soils, where even slight increases in P availability can influence plant performance. Therefore, we aimed to determine whether pasteurisation of extremely P-impoverished soil affects growth of Agonis flexuosa and facilitation by Banksia attenuata . Methods In a controlled experiment, we evaluated plant growth and root traits of target species A. flexuosa grown either in monoculture or mixed culture with B. attenuata , under pasteurised soil treatment (PST) and inoculated soil treatment (IST). Results Soil resin P concentration was 20% higher in PST than in IST. In PST compared with IST, A. flexuosa had greater leaf P concentration (1.1 vs. 0.3 mg g⁻ 1 ) and total biomass (5.0 vs. 3.0 g), developed thicker roots with lower tissue density, and showed higher rhizosheath carboxylate amounts. Under PST, the total biomass of A. flexuosa was greater when grown with B. attenuata (7.4 vs. 5.0 g), accompanied by lower rhizosheath acid phosphatase activity than without B. attenuata , whereas total biomass was indistinguishable under IST. Moreover, growing with B. attenuata , biomass of A. flexuosa under IST was 49% of that under PST. Conclusions Pasteurisation of extremely P-impoverished soil increased P availability, likely through microbial P release and reduced microbial competition, thereby enhancing nutrient-foraging traits of A. flexuosa . Pasteurisation may also modify soil redox conditions and promote the release of Mn- and Fe-bound P. Therefore, experiments using soil pasteurisation should assess microbial biomass and changes in soil nutrient pools.