SULFUR AND IRON GEOCHEMISTRY IN THE RHIZOSPHERE OF WILD RICE (ZIZANIA PALUSTRIS)

Wild rice (Zizania Palustris) is a cultural staple of the Indigenous people of Minnesota as well as an integrated component of the culture in this area. The aquatic sediments where wild rice communities establish their roots are usually anoxic. Photosynthetic processes allow for the transportation of oxygen to the roots. Radial oxygen loss, a process in which wetland plants release oxygen into the sediment, can oxidize ferrous iron and sulfide, and may be the primary mechanism by which wild rice controls the redox environment proximal to its roots. This process has been shown to induce the precipitation of iron-oxides on the root surface. These precipitates provide a barrier to wild rice roots from toxic sulfides which in high concentrations have negative. This study investigates the mechanism of radial oxygen loss (ROL) and how it affects subsurface redox reactions as well as the precipitation of minerals in the rhizosphere during different life stages. In this study, we evaluated the porewater and precipitate concentrations of iron and sulfide in the sediment of two treatments. Sulfide treatment tanks were given 16g of sodium sulfide while non-sulfide tanks served as controls, each of which had six water columns of either 15in or 40in. Measurements were recorded at three different life stages: seedling, floating leaf, and aerial leaf. Sulfur-amended tanks with high porewater sulfide concentrations have higher acid volatile sulfide. These plants also show lower concentrations of iron oxides than control plants. Shallow water columns had greater iron porewater concentrations, but column height did not appear to affect iron oxide formation. The lower concentration of iron oxides in sulfur-amended tanks may be due to a lower rate of radial oxygen loss, or a lower availability of iron to form iron oxides.