Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Master of Science




Macfie, Sheila M.


Cadmium (Cd) is non-essential and toxic. Sulfur (S) addition to contaminated soils reduces Cd toxicity in rice and corn. I aimed to determine the underlying mechanisms by which S reduces Cd toxicity in hydroponically- and soil-grown soybean. In the presence of Cd, plant biomass was reduced by ~20%, Cd accumulated up to 45 μg/g in roots and 15 μg/g shoots, and concentrations of Cd chelators increased by more than 10-fold. Addition of S to Cd- treated plants had no effect on plant biomass, concentrations of Cd in roots and shoots, or vacuolar Cd sequestration in the root cortex. While additional S visibly altered Cd localization in the roots, it had no effect on altering Cd concentration in root plaque. Additional S in the presence of Cd resulted in a 0- to 1.5-fold increase in Cd chelator concentrations; however, addition of S to alleviate Cd toxicity has no benefit in soybean.

Summary for Lay Audience

Cadmium (Cd) concentrations are increasing globally in agricultural soils due to anthropogenic contamination. Although it is a non-essential element, Cd can inhibit plant growth and pose a health risk to consumers. Sulfur (S) addition to Cd-contaminated soils can reduce Cd toxicity in rice and corn. Additional S might enhance the formation of an insoluble plaque (layers of oxidized compounds) on the root surface. Binding of Cd ions to the plaque would reduce Cd uptake. Increased availability of S may also increase the production of S- containing molecules called chelators that bind to and keep Cd within plant cells.

I designed this study to determine the underlying mechanisms behind reduction of Cd toxicity due to S addition in soybean. My specific objectives were to determine if S addition will reduce Cd toxicity by causing increased binding of Cd to the root plaque, decreased Cd uptake, increased chelator production, and increased accumulation of Cd in root cells. Hydroponic and soil experiments were performed.

As expected, biomass of soybean plants was reduced in response to Cd and the concentrations of chelators in roots and leaves increased at least 10-fold. In contrast to results of similar experiments on rice and corn, additional S did not reduce Cd toxicity in soybean, nor did it reduce the concentration of Cd in roots or shoots or cause accumulation of Cd on or in root cells. Additional S did visibly alter Cd localization in the roots but did not alter the concentration of Cd bound to the root plaque. Additional S also resulted in a 0 to 1.5-fold increase in some chelators but the pattern was not consistent with S dose.

Based on the findings of this study it can be concluded that addition of S in the presence of Cd does not reduce toxicity of Cd in soybean as it does in rice and corn. These results would best be applied by agronomists to prevent misconceptions about the benefits of additional S on reducing Cd uptake and toxicity in crop species such as soybean.