Mycorrhizal symbiosis and phosphorus supply determine interactions among plants with contrasting nutrient‐acquisition strategies

Highly diverse plant communities growing on nutrient-impoverished soils are test beds for theories species coexistence. Here, neighbouring mycorrhizal and non-mycorrhizal plants compete limited phosphorus. The impact of below-ground interactions community dynamics is underexplored. We used an experimental approach to investigate effects inoculation with arbuscular (AM) fungi a phosphorus supply gradient competitive facilitative among mixed assemblages woody in microcosms. species, one cluster root-forming (CR) four AM native jarrah forest that grows south-western Australia. measured growth microcosms, without the fungus Rhizophagus irregularis, across P supply: 0, 9, 27 243 mg per kg soil. Our data show evidence plant–plant facilitation at low competition high supply. Growth CR Hakea undulata, was highest microcosms 0P inoculation. One Bossiaea aquifolium, also performed better lower levels, possibly benefitting from mobilised by H. undulata. other three strongly obligates, higher levels. Data Acacia celastrifolia suggested it facultatively mycotropic, because there no correlation between colonisation relative inoculum effect, we suggest positive 9P might be due benefits than acquisition, such as pathogen defence. Benefit diminished level had predicted. fourth Eucalyptus marginata (jarrah), were not inoculated AM, perhaps more ectomycorrhizas. Synthesis. spatial heterogeneity soil P, coupled diversity nutrient-acquisition strategies, plasticity plant–AM interactions, contributes coexistence forest. research highlights importance mechanisms understanding factors determining structure including potential role