BIOAVAILABILITY OF HEAVY-METALS AND ARBUSCULAR MYCORRHIZA IN A SEWAGE-SLUDGE-AMENDED SANDY SOIL

The bioavailability of metals (Cd, Ni, Zn, Cu, Pb and Mn) and abundanc e of arbuscular mycorrhiza were studied in a long-term sewage-sludge f ield trial on an acid sandy soil, at INRA-Bordeaux, France. Zn/Mn-(E1) and Cd/Ni-(E2)contaminated sludge had been applied at two rates (10 t DM ha(-1) y(-1) and 100 t DM ha(-1) 2y(-1)) for 18 and 5 y, respectiv ely. Inorganic fertilizer and farm yard manure treatments served as un polluted controls. Soil extraction with EDTA-NH4OAc and Ca(NO3)(2) and plant (Zea mays L.) uptake demonstrated an unusually high Zn (E1), Cd and Ni (E2) availability in the sludge-amended plots. The spore densi ty of arbuscular mycorrhizal fungi ranged from 16 to 67 spores 50 g(-1 ) dry soil, and root colonization between 0-33%. No relationship betwe en mycorrhizal abundance and degree of metal exposure in soil or insid e plant roots could be established, but root colonization across the d ifferent treatments correlated well with plant P status. The results s uggest a better tolerance of the indigenous population of arbuscular m ycorrhizal fungi to elevated metal than to high P concentrations.