Mycorrhizal associations and soil properties of native Allanblackia stuhlmannii stands in the Eastern Usambara Mountains, Tanzania

Allanblackia stuhlmannii is a tree species currently under domestication. Potential mycorrhizal relationships of A. stuhlmannii and soil properties of native stands were investigated to determine the soil-environmental requirements of the species. Roots and soil samples were collected from five sites with A. stuhlmannii stands along an altitudinal transect in Amani Nature Reserve, Tanzania. Mycorrhizal status was investigated by combining microscopy with molecular analysis of the fungal communities. Soil adjacent to the A. stuhlmannii seedlings was analysed for physical and chemical properties and the sites were characterised. We showed that A. stuhlmannii form symbiosis with arbuscular mycorrhizal fungi, and that there was a diverse microbiome associated with the roots. The soils, classified as Ferralsol and Acrisol, were very well drained, had a pH(CaCl2) generally at or below 4, high exchangeable acidity and content of sesquioxides and low effective cation exchange capacity and concentrations of most nutrients. We conclude that A. stuhlmannii is tolerant to high Al availability and possesses mechanisms for acquisition of P and other macronutrients at low soil availability, possibly through mycorrhizal symbiosis. However, being adapted to low-pH soils, it may be less efficient in acquiring Fe, Mn and/or Zn at higher soil pH. Thus, it may be most suited to introduction on farms situated on acid soils.