Growth of Salvinia molesta as affected by water temperature and nutrition I. Effects of nitrogen level and nitrogen compounds

The growth of Salvinia molesta D.S. Mitchell was studied in a greenhouse using controlled-temperature water-baths at 16, 19 and 22°C and 4 different nitrogen compounds (NO₃^?, NH₄⁺, NH₄NO₃ and urea) at levels up to 60 mg N l^?1. Little growth occurred at 16°C even if 20 mg N l^?1 was supplied together with other nutrients including phosphorus (2 mg H₂PO₄-P l^?1). The highest relative growth rate and total dry matter production occurred at 22°C when plants were supplied with 20 mg NH₄-N l^?1. At this temperature, the NH₄⁺ ion was superior to the NO₃^? ion or urea as a nitrogen source (almost doubling the biomass), but was not significantly better than NH₄NO₃. Over a period of 19 days for plants receiving 0.02 mg NH₄-N l^?, biomass increased 4-fold at 16°C, 9-fold at 19°C and 10-fold at 22°C. In contrast, for plants receiving 20 mg NH₄-N l^?1, biomass increased 4-fold at 16°C, 18-fold at 19°C and 38-fold at 22°C.