Nitrogen uptake and assimilation in Enteromorpha intestinalis (L.) Link (Chlorophyta):: using 15N to determine preference during simultaneous pulses of nitrate and ammonium

We investigated the ability of Enteromorpha intestinalis (L.) Link to take up pulses of different species of nitrogen simultaneously, as this would be an important mechanism to enhance bloom ability in estuaries. Uptake rates and preference for NH4+ or NO3- following 1, 3, 6, 9, 12 or 24 h of exposure to either (NH4NO3)-N-15 or (NH4NO3)-N-15 were determined by disappearance of N from the medium. Differences in assimilation rates for NH+4 or NO3- were quantified by the accumulation of NH4+, NO3-, and atom % N-15 in the algal tissue. NH4+ concentration was reduced more quickly than water NO3- concentration. Water column NH4+ concentration after the longest time interval was reduced from 300 to 50 muM. Water NO3- was reduced from 300 to 150 muM. The presence of N-15 or N-14 had no effect on uptake of either NH4+ or NO3. N-15 was removed from the water at an almost identical rate and magnitude as N-14. Differences in accumulation of (NH4+)-N-15 and (NO3-)-N-15 in the tissue reflected disappearance from the water; N-15 from NH4+ accumulated faster and reached an atom % twice that of N-15 from NO3-. This outcome suggested that when NH4+ and NO3- were supplied in equal concentrations, more NH4+ was taken up and assimilated. The ability to take up high concentrations of NH4+, and NO3- simultaneously is important for bloom-forming species of estuarine macroalgae subject to multiple nutrient species from various sources. (C) 2004 Elsevier B.V. All rights reserved.