The Role of Arbuscular Mycorrhizal Fungi in Mediating Heavy Metal Tolerance and Accumulation in Two Plant Specie

The contamination of our planet's soils by anthropogenically produced compounds such as heavy metals and excess nutrients is an increasing ecological problem. From harmful effects on wildlife, physiological disruptions in humans, bioaccumulation in food webs, and the poisoning of soils that we depend on for food production, soil pollution threatens the health of our planet. Pollution is ubiquitous in urban areas, particularly where fossil-fuel driven activities occur. Conventional soil remediation approaches such as excavation and replacement have limitations including high cost and disruption of soil microbiomes. Phytoremediation, or the use of plants to remove contaminants from soil, is a cost-effective and environmentally conscious approach that is emerging in the field of environmental restoration. Current research in this field aims to better understand the dynamic soil/plant/microbial interactions, as well as which species can tolerate and accumulate contaminants at the highest rate. The major goals of this project were to determine the phytoremediation potential of two plant species, the common sunflower (Helianthus annuus) and Sunn Hemp (Crotalaria juncea), and to evaluate the role of arbuscular mycorrhizal fungi (AMF) in heavy metal stress mitigation and accumulation. Plants were grown in a research greenhouse on the University of Central Arkansas campus between May and August of 2017. Solutions containing copper sulfate (CuSO4), cadmium sulfate (CdSO4) and lead nitrate (Pb(NO3)2) were applied in three doses (low, medium, and high), and predawn measurements of maximum quantum yield (Fv/Fm) were taken weekly. Plants were harvested after 7 weeks, separated into above and below ground samples, and analyzed with Flame Atomic Absorption Spectroscopy (FAAS) for heavy metal content. Results indicate that AMF had a negligible effect on mitigating Fv/Fm in both species, as well as accumulation capacity. Lead and copper were accumulated in concentrations that were below the detection limit of the FAAS. Helianthus annuus accumulated significantly more cadmium than C. juncea , and both species accumulated significantly more heavy metals in their below ground tissues than were translocated to their above ground tissue. Overall, H. annuus has the greater phytoremediation potential of the two plant species based on its ability to maintain high Fv/Fm values despite growing in highly toxic soil, and its high capacity to accumulate cadmium.