Context-dependent colonisation of Banksia species by arbuscular mycorrhizal fungi across contrasting rainfall regions

Abstract

The absence of a suberised exodermis in Banksia (Proteaceae) roots enables rapid carboxylate release for phosphorus mobilisation but also increases their susceptibility to soil pathogens. Recently, evidence of arbuscular mycorrhizal (AM) colonisation in Banksia species from high-rainfall regions prompted a reassessment of the association between Banksia species and AM fungi. We collected root and soil samples from Banksia attenuata and B. sessilis at two contrasting rainfall sites to characterise the AM fungal communities. We also isolated oomycetes from the soil samples and conducted a glasshouse experiment using the native soils to verify the presence of viable AM fungi. At the high-rainfall Warren site, both Banksia species showed AM colonisation and five oomycetes were isolated, whereas no colonisation and only one oomycete occurred at the drier Jurien Bay site. In both species, AM fungal alpha diversity was lower in root samples than in soil samples, with roots dominated by Glomeraceae and soils enriched in Gigasporaceae and Acaulosporaceae. Additionally, Endogonaceae occurred in B. attenuata roots but were largely absent from B. sessilis . These results demonstrate that the two Banksia species maintain context-dependent mycorrhizal associations under moist conditions, challenging their conventional classification as non-mycorrhizal.