Date of Award
Summer 7-15-2016
Degree Type
Thesis
Degree Name
Master of Science in Integrative Biology (MSIB)
Department
Biology
Committee Chair/First Advisor
Marina Koether
Major Professor
Sigurdur Greipsson
Second Committee Member
Joel McNeal
Abstract
Soil lead (Pb) contamination represents a major environmental and public health risk. Conventional Pb remediation methods are typically expensive and risk further environmental damage. Phytoextraction has emerged as an alternative heavy metal remediation method with the potential for reducing both economic cost and negative environmental effects. For this study, North American native switchgrass (Panicum virgatum) was chosen due to its ability to achieve high biomass yields across a variety of climates and environmental conditions. The switchgrass plants in this study were treated with chemical chelates, fungal suppressants, and nitric oxide (NO) donors with the intent of optimizing Pb phytoextraction.
Soils collected from sites located in urban Atlanta were chemically manipulated with the intent to increase Pb bioavailability and uptake into harvestable switchgrass tissues. Ethylenediamintetraacetic acid (EDTA) is regarded as a highly effective chelate, though its long soil persistence leads to potential concerns about Pb mobilization into groundwater. Citric acid has been proposed and found success as an alternative chelate that has a significantly shorter soil persistence time and lower risk of ground water contamination; though its abilities to chelate Pb in a phytoextraction context are still being studied. In addition to a comparison of chelating agents, two fungal suppressants were also compared for their abilities to suppress arbuscular mycorrhizal fungi (AMF). Benomyl is frequently used as a fungal suppressant in phytoextraction research, but another alternative, propiconazole may be a more effective fungal suppressant.
Exogenous nitric oxide (NO) donor application was also studied to determine the effects on switchgrass biomass and Pb uptake. Three exogenous NO donors were evaluated in the primary study: S-Nitroso-N-acetylpenicillamine (SNAP), sodium nitroprusside (SNP), and S-nitrosoglutathione (GSNO). Each exogenous NO donor was tested at multiple concentrations in the initial study, though no significant difference was found between any donor and concentration. In the second study, SNP (0.5 μM) was selected for application, but no significant difference was found between plants in SNP treatments and non-SNP treatments.
In the second study, chemical applications of EDTA, citric acid, benomyl, propiconazole, and SNP were tested in combinations of chelate, fungal suppressant and NO donor or non-donor applied treatments. While both chelates exhibited increased Pb accumulation over the Control plants, the EDTA treatments showed increased Pb accumulation in both root and shoot tissues over the citric acid treatments. Despite the differences in Pb accumulation, there was no significant difference between translocation factors between any treatments. Total Pb phytoextraction was highest in EDTA chelate treatments with application of benomyl (EB) and propiconazole (EP).
Application of benomyl and propiconazole demonstrated the ability of both broad-spectrum fungicides to reduce AMF colonization, allowing greater Pb phytoextraction; however, roots treated with propiconazole exhibited significantly decreased AMF colonization in comparison to roots treated with benomyl. Additionally, benomyl application resulted in significantly increased colonization of pathogenic fungi over the Control plants, while propiconazole application significantly reduced pathogenic fungi colonization.