Abstract: | The uptake of nitrate, nitrite and ammonium by Codium fragile subsp. tomentosoides (van Goor) Silva was measured at different combinations of temperature (6–30 C) and irradiance (0–140 μEin.m-2. s-1). Uptake of all three forms of N was greater at 12–24 C than at 6 and 30 C. Although uptake was stimulated by light, saturation occurred at relatively low irradiance (7–28 μEin m-2 s-1, depending on the N source and temperature). The Michaelis-Menten uptake constants (Vmax K)varied with temperature. Vmax was greatest at intermediate temperatures and K was lowest at lower temperatures. The Vmaxfor NH4+ was higher and the K, for NH4+was lower than those for NO3-- and NO2--. Codium was capable of simultaneously taking up all three forms of inorganic N although the presence of NH4+ reduced the uptake of both NO3-- and NO2--. The results of this study indicate that part of the ecological success of Codium in a N-limited environment may be due to its N uptake capabilities. |