Submitted to: Water, Air, and Soil Pollution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/2009
Publication Date: 2/18/2010
Citation: Pierce, S.C., Moore, M.T., Larsen, D., Pezeshki, S.R. 2010. Macronutrient (N,P,K) and redoximorphic metal (Fe,Mn) allocation in Leersia oryzoides (rice cutgrass) grown under different flood regimes. Water, Air and Soil Pollution. 207:73-84. Interpretive Summary: The use of plants to clean up contaminants (phytoremediation) is growing in popularity among farmers and conservationists. Using vegetated drainage ditches is an economical and environmentally sound way to help alleviate contaminants associated with agricultural runoff. However, little research has examined the plant physiological responses, including nutrient uptake, when exposed to variable flooding regimes. Results from this study indicated that rice cutgrass, a common drainage ditch species, can indirectly affect nutrient and metal concentrations in runoff water through soil reduction-oxidation processes.
Technical Abstract: Vegetated drainages are an effective method for removal of pollutants associated with agricultural runoff. Leersia oryzoides, a plant common to agricultural ditches, may be particularly effective in remediation; however, research characterizing responses of L. oryzoides to flooding are limited. Soil reduction resulting from flooding can change availability of nutrients to plants via changes in chemical species (e.g. - increasing solubility of Fe). Additionally, plant metabolic stresses resulting from reduced soils can decrease nutrient uptake and translocation. The objective of this study was to characterize belowground and aboveground nutrient allocation of L. oryzoides subjected to various soil moisture regimes. Treatments included: a well-watered, well-drained control; a continuously saturated treatment; a 48-hour pulse-flood treatment; and a partially flooded treatment in which water-level was maintained at 15 cm below the soil surface and flooded to the soil surface for 48 hours once a week. Soil redox potential (Eh, mV) was measured periodically over the course of the 8 week experiment. At experiment termination, concentrations of Kjeldahl Nitrogen, Phosphorus (P),Potassium (K), Iron(Fe), and Manganese (Mn) were measured in plant tissues. All flooded treatments demonstrated moderately reduced soil conditions (Eh <350 mV). Plant Kjeldahl nitrogen concentrations demonstrated no treatment effect, whereas P and K concentrations decreased in aboveground portions of the plant. Belowground concentrations of P, Mn, and Fe were significantly higher in flooded plants, likely due to the increased solubility of these nutrients resulting from the reductive decomposition of metal-phosphate complexes in the soil and subsequent precipitation in the rhizosphere. These results indicate that wetland plants may indirectly affect P, Mn, and Fe concentrations in surface waters by altering local trends in soil oxidation-reduction chemistry.