Use of Cannabis sativa L. for Improving Cadmium-Contaminated Mediterranean Soils—Effect of Mycorrhizal Colonization on Phytoremediation Capacity

Although the phytoremediation strategy has been studied worldwide, little research data are available regarding the influence of mycorrhizae on the phytoremediation capacity of various plants grown in Cd-contaminated soils in Mediterranean environments. Therefore, a pot experiment was carried out to study the possible effectiveness of hemp plant (Cannabis sativa L.) in the remediation of moderately and heavily Cd-contaminated soils and additionally to quantify the effect of Cd on Arbuscular Mycorrhizal Fungi (AMFs). For this purpose, an alkaline clay soil collected from the Farm of Institute of Plant Breeding and Genetic Resources (North Greece) was contaminated with two levels of Cd (3 and 30 mg Cd kg−1, corresponding to Levels A and B, respectively—first factor) at two incubation times (10 and 30 days—second factor) and six treatments (Control_30d, Control_10d, CdA_30d, CdB_30d, CdA_10d, CdB_10d) were created. Soil Cd concentrations, both pseudo-total and available to plants, were determined after extraction with Aqua Regia mixture and DTPA solution, respectively, before and after the cultivation of hemp plants and after the harvesting. Cd concentrations in the aboveground and underground plant parts were also estimated after digestion with Aqua Regia, while root colonization by AMFs was determined with a microscope. The highest plant’s Cd concentration, more than 50%, was observed in its underground part, at all Cd-contaminated treatments, indicating a strong capacity for cadmium to gather up in the roots. Among different Cd levels and incubation days, significant differences were recorded in the rates of root colonization by AMFs. Among different Cd levels and incubation days, 3 mg Cd Kg−1 soil promoted AMF root colonization, particularly at 10-day incubation, while 30 mg Cd Kg−1 soil diminished it. Colonization was lower with longer incubation times at both levels of Cd. Hemp appears to be a viable option for phytostabilization in Cd-contaminated soils, enabling further utilization of AMFs to assist the phytoremediation process.