Effect of indigenous and introduced vesicular-arbuscular mycorrhizal fungi on growth and phosphorus uptake of Trifolium pratense and on inorganic phosphorus fractions in a cambisol

Summary Five selected vesicular-arbuscular mycorrhizal (VAM) fungi and the native population of a cambisol were tested in sterilized soil conditions, with Trifolium pratense as host plant. Indigenous fungi were the most effective in enhancing plant growth and P uptake, which were correlated with a higher root colonization. Selected fungi did not spread further in the root after 4 months from sowing, occupying less than 10% at the end of the experiment; inoculation with Glomus fasciculatum E3 yielded a higher dry-matter production than any other VAM species, but did not significantly increase shoot P concentration above that of the non-mycorrhizal control. Interactions between indigenous and introduced VAM fungi were studied in unsterilized soil. Results from fresh and dry weights of shoots and the percentage of fungal infection showed that the native endophytes competed more efficiently in colonizing the root. Inoculation with selected VAM species did not improve plant growth. Sterilization altered the inorganic P fractions of the soil, particularly those extracted with NH₄F and NaOH. Sterilized soil contained less inorganic P than unsterilized soil, but more soluble P. By the end of the experiment in sterilized soil, P extracted with NH₄Cl, NH₄F and NaOH and total inorganic P were significantly different among inoculation treatments, suggesting that VAM fungi may differ in their ability to take up P.