Iron and Sulfur Cycling in the Rhizosphere of Wild Rice (Zizania palustris)

Wild rice (Zizania palustris), an annual macrophyte with significant cultural, economic, and ecological value, grown in high sulfate develops black iron sulfide precipitates on root surfaces, and produces fewer and lighter seeds, leading to decreased populations long-term. To investigate the role of iron sulfide precipitates in impaired seed production, wild rice plants grown in buckets were exposed to 300 mg/L of sulfate, and harvested biweekly for extraction of root acid volatile sulfide (AVS) and weak acid extractable iron and analysis of plant and seed N. In sulfate-amended plants, root AVS accumulated rapidly just prior to seed production. Simultaneously, iron speciation of the root precipitate shifted from Fe(III) to Fe(II), consistent with a transition from iron (hydr)oxide to iron sulfide. Sulfate-amended plants produced fewer, lighter seeds with less nitrogen. It is suggested that sulfide inhibits N uptake, causing rapid AVS accumulation during the reproductive life stage to disproportionately harm seed production.