The Influence of Soil pH on the Efficiency of Vesicular-Arbuscular Mycorrhiza

Tagetes minuta and Guizotia abyssinica reacted differently to changes in soil pH and to fertilization with various phosphates in spite of inoculation with the same strain of Glomus macrocarpus. At pH 4.3, mycorrhizal Guizotia was unable to absorb P from all the compounds with the result that growth was severely inhibited by inoculation, whereas mycorrhizal Tagetes grew well at this pH in the presence of Ca(H2PO4)2. H2O, Ca5(PO4)3OH and AIPO4. Phosphorus uptake and growth of mycorrhizal Guizotia were improved at pH 5.6 and surpassed the performance of non-mycorrhizal plants at pH 6.6. Growth of mycorrhizal Tagetes was reduced at pH 5.6 in the presence of Ca(H2PO4)2. H2O and Ca5(PO4)3OH, but improved at pH 6.6 in all treatments with the exception of Ca5(PO4)3OH as P source.