A cool spot in a biodiversity hotspot: why do tall Eucalyptus forests in Southwest Australia exhibit low diversity?

Abstract Background and aims Southwest Australia is a biodiversity hotspot, with greatest plant species diversity on the most severely phosphorus (P)-impoverished soils. Here, non-mycorrhizal highly-effective carboxylate-releasing P-acquisition strategies coexist mycorrhizal that are less effective at accessing P these Non-mycorrhizal facilitate acquisition of neighbours better defended against pathogens. In Australian Biodiversity Hotspot, there also ‘cool spots’ low-diversity tall Eucalyptus communities P-impoverished These trees obviously do not require facilitation their by neighbours, because only minor component communities. We hypothesised in forests, release carboxylates to acquire P. Thus, they would depend facilitation, must be strong competitors. However, external hyphae P, able access soil organic nitrogen (N), for which need hyphae. Methods Since mobilise but manganese (Mn), we used leaf Mn concentrations ([Mn]) natural habitat proxy rhizosphere carboxylates. To verify this proxy, measured carboxylate exudation targeted high [Mn] using seedlings grown low-P nutrient solutions. Results Using complementary approaches, confirmed our hypothesis dominant mineralisation N associated fractionation N, enriching 15 while nitrate depleted stable isotope composition material. The results show did despite being ectomycorrhizal. Conclusions low forests southwest can explained exhibiting strategy. eucalypts therefore competitors N.