Plant senescence: a mechanism for nutrient release in temperate agricultural wetlands.

The beneficial uptake of nutrients by wetland plants is countered to some extent by nutrient release back into the aquatic environment due to vegetative die-back. This current study examined whether Leersia oryzoides, a common wetland plant, exhibits luxury uptake of nutrients from simulated farm runoff. The study also tested whether with subsequent decomposition, these nutrients are released back into the water column. When exposed to elevated (>2mg/L N and P) runoff, L. oryzoides assimilated significantly higher concentrations of nitrogen (p<0.001) and phosphorus (p<0.001) in above-ground biomass as compared to non-enriched treatments (<0.05 mg/L N and P). Subsequently, senescence of enriched above-ground biomass yielded significantly higher concentrations of phosphorus (2.19+/-0.84 mg P/L). Using L. oryzoides as our model, this study demonstrates nitrogen and phosphorus sequestration during the growing season and release of phosphorus in the winter.