EFFECT OF AMMONIUM-IONS ON THE NET PHOTOSYNTHESIS OF 3 SPECIES OF ELODEA

Three species of Elodea, E. canadensis Michx., E. ernstae St John and E. nuttallii St John were contaminated with concentrations of NH4+ occ urring in the environment at 0.25, 0.50 and 1 mg 1(-1) and also with c oncentrations, clearly greater than natural values, of 2.5, 5.0 and 7. 5 mg 1(-1). These assays were carried out over a 7 day test period. Th e effects of ammonium were investigated by measuring the net photosynt hesis and residue analyses of the active substance in water were also carried out. Three different significant types of reaction were found: (1) strong concentrations of ammonium nitrogen (1-7.5 mg l(-1) of N-N H4+) do not affect the photosynthetic activity of E. ernstae; (2) thes e concentrations stimulate the photosynthesis off, nutlallii; (3) they inhibit the photosynthesis of E. canadensis.