Under oxygenated conditions, sulfate is relatively non-toxic to aquatic plants. However, where oxygen is absent and organic matter is present, sulfate can be reduced to toxic sulfide. Although the direct effects of sulfate and sulfide on the physiology of a few plant species have been studied in some detail, their cumulative effects on a plant’s life cycle and population dynamics through possible inhibition of seed germination, seedling survival, growth, and seed production have been less well studied. We investigated the effect of sulfate and sulfide on the life cycle of wild rice (Zizania palustrisL.) in hydroponic solutions and in outdoor mesocosms with sediment from a wild rice lake.
Results/Conclusions
In hydroponic solutions, sulfate had no effect on seed germination or juvenile seedling growth and development, but sulfide greatly reduced juvenile seedling growth and development at concentrations greater than 320 μg · L-1. In outdoor mesocosms, sulfate additions to overlying water strongly increased sulfide production in sediments. Wild rice seedling emergence, seedling survival, biomass growth, viable seed production, and seed weight all declined with sulfate additions and hence sulfide concentrations in sediment. These declines grew steeper during the course of the five years of the mesocosm experiment and wild rice populations became extinct in most tanks with concentrations of 250 mg SO4 · L-1 or greater in the overlying water. Iron sulfide precipitated on the roots of wild rice plants, especially at high sulfate application rates. These precipitates may impede nutrient uptake and be partly responsible for the reduced seed production and viability.