DEL VAL MUņOZ, CORAL, JOSE MIGUEL BAREA & CONCEPCION AZCÓN-AGUILAR.
Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Profesor Albareda 1, 18008 Granada, SPAIN.
High concentrations of heavy metals have shown adverse effects on soil microbial populations, their diversity and activity. Therefore, the effect of any soil treatment which might increase heavy metal content can, consequently, affect soil microbial populations. The aim of this work was to study how diversity of arbuscular mycorrhizal (AM) fungi is affected by the addition of sewage amended sludge in a long-term experiment, as well as the level of tolerance and adaptation to heavy metals of the indigenous AM fungal populations. Six species of AM fungi were found in the experimental soils, their behaviour ranging from very sensitive, relatively resistant or even tolerant to the metals. Total AM fungal spore numbers decreased with increasing amounts of heavy metals in the soil, whereas species richness and the Shannon-Wiener diversity index increased at moderate levels of soil contamination, but decreased in soils that had recieved the highest amounts of heavy metals with the contaminated sludge. Four AM fungal species were successfully isolated from the experimental plots: i) Glomus claroideum isolated from plots without sludge addition; ii) Glomus claroideum, isolated from the most contaminated plots; iii) a unidentified Glomus sp. present only in less contaminated plots and iv) Glomus mosseae, isolated from medium contaminated plots. There were consistent differencies in behaviour among the four indigenous AM fungi isolated with regards to the mycorrhizal colonization levels they produced in non-contaminated and contaminated soils. The main conclusions of this study are: (i) Glomus sp. and G. mosseae isolates are strongly inhibited by heavy metals, which mainly acted by inhibiting the growth of the external mycelium; (ii) there is a potential adaptation of the G. claroideum isolates, particularly for the G. claroideum from the most contaminated soil.