UPTAKE OF INORGANIC NITROGEN BY CODIUM FRAGILE SUBSP. TOMENTOSOIDES (CHLOROPHYTA)

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. Copyright © 1978, Wiley Blackwell. All rights reserved