The Effect of Heavy Metal Speciation on Arbuscular Mycorrhizal Fungi Associated with Phoenix dactylifera L. Growing in Moroccan Urban and Peri-Urban Environments

Description of the subject. Impact of anthropogenic activities via metal pollution on Arbuscular Mycorrhizal Fungi (AMF) in rhizopheric soils of date palms in urban and peri-urban areas. Objective. The study’s objective was to assess the impact of rhizospheric soil contamination via various chemical species of heavy metals on the AMF spore density associated with date palms. Methods. A collection of date palm’s rhizospheric soil samples from eight sites including three boulevards, three gardens and two distinct areas of the Marrakesh palm grove. These samples were used for counting endomycorrhizal fungal spores, for estimating mycorrhization state of root system and for physico-chemical analyzes. A five-stage sequential extraction scheme was used to evaluate the fractionation of some heavy metals (Pb, Cd, Cu, Zn and Fe). Pearson’s correlation coefficients between AMF spore’s density and metal species were determined and a multiple linear regression was tested to predict AMF spore density from chemical species content of soil. Results. A mycorrhizal dependency of date palm was indicated, since a high frequency (61 to 98%) and a middle intensity (10 to 47%) of root colonization by AMF were recorded. The spore density from all sites was found in increasing order of boulevards, garden then palm groves. A significant correlation between AMF spores’ density and some metal species rhizospheric soil content was recorded ; negative for sulphide-bound [ lead (r = - 0.81) and Zinc (r = - 0.70) ] and for exchangeable fraction Copper (r = - 0.79) whereas it's positive for exchangeable fraction Zinc (r = 0.70). AMF spores’ density predictions from Sulphide-bound Zinc and exchangeable fraction Copper exhibited a good fit, with higher R2 value (0.91, p = 0.002). Conclusions. Since Date palm has a mycotrophic nature, the sustainability of the microbial populations associated with their roots might be ensured by modifying some chemical forms of heavy metals like Sulphide-bound Zinc and exchangeable fraction Copper.