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 abundance of arbuscular mycorrhiza were studied in a long-term sewage-sludge field trial on an acid sandy soil, at INRA-Bordeaux, France. ZnMn-(E1) and CdNi-(E2)contaiminated sludge had been applied at two rates (10t DM ha−1 y−1 and 100 t DM ha−1 2y−1) for 18 and 5 y, respectively. Inorganic fertilizer and farm yard manure treatments served as unpolluted 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 density of arbuscular mycorrhizal fungi ranged from 16 to 67 spores 50 g−1 dry soil, and root colonization between 0–33%. No relationship between mycorrhizal abundance and degree of metal exposure in soil or inside plant roots could be established, but root colonization across the different treatments correlated well with plant P status. The results suggest a better tolerance of the indigenous population of arbuscular mycorrhizal fungi to elevated metal than to high P concentrations.