Browsing by Author "LaFond-Hudson, Sophia"

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    Biogeochemical Interactions And Ecological Consequences Of Sulfur In Stands Of Wild Rice
    (2020-05) LaFond-Hudson, Sophia
    Wild rice is an ecologically and culturally important plant that typically grows in lakes and rivers in Minnesota that have low sulfate concentrations. Previous work demonstrated that elevated sulfate concentrations contribute to the decline in wild rice populations when conditions allow for the reaction of sulfate to sulfide. This dissertation investigates the fate of sulfate in the rooting zone of wild rice, mechanisms and consequences of sulfide exposure to plants, and the long-term effects of sulfide exposure on population dynamics. Key findings include 1) iron plaques on root surfaces transition from iron oxide to iron sulfide during reproduction if sulfate is elevated; 2) in elevated sulfate, seed production is delayed and shortened and plants produce fewer, smaller seeds with less nitrogen; and 3) populations of wild rice grown in low sulfate have stable biomass oscillations with a period of approximately 4 years, but elevated sulfate destabilizes these cycles and drives the population toward extinction.
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    Iron and Sulfur Cycling in the Rhizosphere of Wild Rice (Zizania palustris)
    (2016-08) LaFond-Hudson, Sophia
    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.
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    Iron Sulfide Formation on the Root Surfaces of Wild Rice
    (2017-08-16) LaFond-Hudson, Sophia; Johnson, Nathan; Pastor, John; Dewey, Brad; lafo0062@d.umn.edu; LaFond-Hudson, Sophia
    The data are from an experiment showing life-cycle induced iron sulfide formation on root surfaces of wild rice. Plants with and without added sulfate were harvested during the reproductive stage of the life cycle to quantify concentrations of iron and sulfide on root surfaces. Seed and plant N was measured to examine the effect of iron sulfide root plaques on seed production. On amended roots, iron transitioned from mostly Fe(III) to mostly Fe(II) as sulfide concentrations increased rapidly. Amended plants produced fewer, lighter seeds with less nitrogen.
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    Supporting data for "Sulfur geochemistry impacts population oscillations of wild rice (Zizania palustris)"
    (2020-07-10) LaFond-Hudson, Sophia; Johnson, Nathan W; Pastor, John; Dewey, Brad; lafo0062@d.umn.edu; LaFond-Hudson, Sophia
    Wild rice populations decline with exposure to elevated sulfate due to production of sulfide in anoxic sediment. Using self-sustaining wild rice mesocosms, we collected data on the population response to sulfate, as well as iron and litter, which both may modify the production and availability of sulfide to plants. Wild rice also experiences natural population oscillations due to delays in release of nitrogen from decomposing litter. We use this data to investigate how sulfate-induced population declines interact with stable litter-driven population cycles. Population data was collected 2014-2019, and geochemical data (iron, sulfide, pH) was collected in 2019, after 5 years of of a factorial design treatment (sulfate, iron, litter).