Conventional industrialized agricultural systems often include the use of irrigation and agrichemicals, such as fertilizers and pesticides, which are used extensively to increase the level of food production, all of which impact the state of the global environment. Agricultural drainage ditches are wetlands linking the agricultural surface and subsurface flow to receiving waters. Plants diversify the agricultural landscape, creating a buffer zone, taking up excess nutrients in the waterway. Well-developed root systems and rapid growth rate are structural aspects that improve contaminant uptake. The objectives of the present study were to quantify the physiological and growth responses of Leersia oryzoides, rice cut grass, to changes in soil flooding and nitrogen.

The experiment was a complete 3X3 factorial design with three levels of flooding intensity; 1) well-watered, well-drained control (C), 2) partially flooded treatment (water maintained at 15 cm below soil surface) (PF), and 3) continuously flooded treatment (water maintained 5 cm above the soil surface) (CF)  and three levels of nitrogen nutrition (NH₄NO₃); 15 ppm, 50 ppm, and 100ppm. Each treatment was replicated 15 times for 135 plants total. Pots were placed in a completely randomized design. The study was terminated 6 weeks after flooding treatment initiation.

Results/Conclusions

Following the initiation of the flooding treatment, both net photosynthesis and stomatal conductance decreased as flooding intensified in CF plants; however both recovered two weeks later. After the 2^nd nitrogen pulse, leaf chlorophyll content was highest in PF treatment, net photosynthesis and leaf chlorophyll content increased at higher nitrogen concentrations, and yield of energy conversion in light adapted leaves decreased with increased flooding in higher nitrogen treatments. Plants in PF conditions produced more above- and belowground biomass than other treatments. Plants had higher aboveground to belowground ratio in response to severity of flooding and higher nitrogen concentration. 

The increase in chlorophyll content and growth of Leersia oryzoides in partially flooded treatments and in response to increased nitrogen concentrations may explain the persistence of this species in agricultural ditches. Developmental changes of individual plants can eventually lead to changes in community structure and function. By assessing plant functions, we will have a better understanding of specific services a particular species may offer such as the ability to mitigate nitrogen from runoff.