The effect of low-dose, commercially available wastewater sludge compost (WSC; 15 t ha⁻¹) treatment was examined with or without arbuscular mycorrhizal fungal (AMF) inoculation on the nutritional status, heavy metal (HM) concentration and the rhizosphere activity of giant reed (Arundo donax L. var. BL clone (Blossom)) plants. Funneliformis mosseae (BEG12; AMF1), F. geosporum (BEG11; AMF2) or their combination (AMFmix) were applied as AMF treatments in a short-term pot experiment. The physiological and growth parameters of the host plants, the AMF root colonization and the microbiological enzyme activity of the mycorrhizosphere were examined. We assumed that the combined treatment (WSC + AMF) enhances the fertility of low-fertility acidic sandy soil. Neither the WSC treatment nor the AMF inoculations changed the extent of root colonization. Based on the results of root electrical capacitance and the phosphorous uptake, plant nutritional status was improved by WSC addition, without any negative impacts among the measured parameters. AMF treatments increased the enzyme activity in the soil and decreased the concentrations of the potentially toxic HMs (Cu, Mn, Pb, Zn) in roots, but that mitigation of Cu and Zn was compensated in shoots. According to the results of MicroResp™ measurements, the catabolic activity profile of the soil microbial community was changed in case of the AMF2 treatment. The efficient regulatory mechanism of giant reed might be able to adjust optimal/maximal colonization rate, and to select the preferential AMF partners, this supposed mechanism might be responsible for its invasiveness and tolerance to a wide range of environmental conditions.