Greenhouse study of nutrient and growth responses of a ditch plant, Leersia oryzoides (rice cutgrass), to varying degrees of soil saturation and water nitrogen concentration

Background/Question/Methods

Vegetated drainage ditches are effective in the removal of contaminants associated with agricultural runoff. Increasingly, research has focused on the efficacy of wetland plants to mitigate and diffuse agricultural runoff in agricultural drainage ditches to better manage and protect fresh water. Leersia oryzoides (rice cutgrass), a plant common to agricultural ditches, may be particularly effective in the remediation process. The objective of this greenhouse study was to evaluate leaf, stem, rhizome, and adventitious root biomass and nutrient allocation of L. oryzoides subjected to various soil moisture and aqueous N input regimes. The experiment was a complete 3X3 factorial design with three levels of flooding intensity and three levels of nitrogen addition (NH₄NO₃-N). All flooded treatments demonstrated reduced soil conditions (Eh < 350 mV). Each treatment was replicated 15 times for 135 plants total. The study was terminated six weeks after flooding treatment initiation. At experiment termination, biomass and elemental concentrations including total nitrogen (N), aluminum (Al), boron (B), calcium (Ca), copper (Cu), Iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), sodium (Na), phosphorus (P), sulfur (S), and zinc (Zn) were measured in plant tissues.

Results/Conclusions

Biomass of leaf (57.7% and 51.3%), stem (58.4% and 47.2%), and adventitious root (86.7% and 59.2%) was significantly higher in partially flooded plants compared to other treatments (control and continuously flooded, respectively). Control and partially flooded plants allocated more resources to rhizome production (93.9% and 131.3%) than continuously flooded plants. Flooding treatments significantly affected elemental concentrations of Cu, Mg, S, and Zn in leaves, Mg and Zn in stems, Cu, Fe, K, and Na in rhizomes, and Cu, Mn, Na, S, and Zn in adventitious roots. The N input regimes significantly affected concentrations of P and S in adventitious roots. These results indicate that L. oryzoides may significantly affect elemental concentrations in surface waters by its ability to uptake various elements and subsequent sequestration in various biomass components. Thus, this species may serve well as a component of a vegetation buffer.