Jackie M. Hill (Department of Zoology and Entomology, Rhodes University), Zuma B. (Institute of Environmental Biotechnology, Rhodes University) and Martin P. Hill (IsoEnvironmental CC, South African Institute for Aquatic Biodiversity, Grahamstown).

Excessive nitrogen loading is a primary driver behind the global deterioration of aquatic ecosystems and the establishment of invasive weeds.

This study aimed to investigate preferential nitrogen uptake on N-fixing Spirodela over a range of concentrations as well as to investigate the effect of an N-fixing symbiosis on Spirodela nitrogen uptake and assimilation through the application of enriched isotopes.

Spirodela plants exposed to both NH4 and NO3 showed a preference for NH4 over NO3 in all medium high concentrations, but did not differentiate between nitrogen forms at low concentrations.

Uptake was similar for NH4 and NO3 in treatments where only one form of nitrogen was available. Neither the application of antibiotics or fungicide had significant effects on the uptake rates of NH4 and NO3 by Spirodela.