Flood responses of Leersia oryzoides and Bacopa monnieri: Implications for water quality in agricultural drainage ditches.

摘要

Laboratory and greenhouse experiments were conducted using mesocosms, comparing flood responses of two species common to rural drainage ditches in the lower Mississippi Alluvial Valley. Leersia oryzoides and Bacopa monnieri were subjected to four treatments: (1) a well-watered, well-drained control, (2) an intermittently flooded treatment, (3) a partially flooded treatment, and 4. a continuously flooded treatment. Over the course of these experiments, soil redox potential (Eh) decreased in flooded treatments, while aerated conditions were maintained in the control. L. oryzoides was fairly resilient to flooding, demonstrating increased biomass, and no effect on root depth under any flooding regime. However, rhizome penetration depth and eventually, net photosynthesis was reduced in the continuously flooded treatment. While macronutrient concentrations in aboveground tissues of L. oryzoides decreased slightly in response to flooding, belowground concentrations of iron and phosphorus, and belowground and aboveground manganese concentrations increased. B. monnieri exhibited decreased root penetration and aboveground concentrations of nitrogen and phosphorus in response to flooding, with greater effects observed under partial and continuously flooded treatments. Soil Eh was significantly lower in flooded treatments of L. oryzoides when compared to B. monnieri. L. oryzoides demonstrated greater overall uptake of phosphate than B. monnieri resulting in lower concentrations of phosphate in effluent from mesocosms containing L. oryzoides. Several interactions were noted. For instance, in the control soil nitrogen was higher in L. oryzoides mesocosms than in B. monnieri mesocosms. Additionally, specific conductivity of effluent from B. monnieri mesocosms increased in response to flooding, an effect that was not observed in L. oryzoides mesocosms.