SHORT TERM UPTAKE OF NUTRIENTS BY ENTEROMORPHA PROLIFERA (CHLOROPHYCEAE)1

Abstract

ABSTRACTRates of NH4+ and NO3− uptake were determined by accumulation of 15N in plant tissue and by disappearance of nutrient from the medium. Agreement between rates calculated by the two methods was good, averaging 82.7% (SD = 15.8%) and 91.2% (SD = 13.7%) for NH4+ and NO3− uptake, respectively. An average of 93.4 and 96.0% of added 15NH4+ and 15NO3− was recovered from the medium and /or plant tissue at the end of the incubations. Both bacterial uptake and regeneration of NH4+ may contribute to discrepancies between NH4+ uptake rates calculated by 15N accumulation and disappearance of NH4+ from the medium.The influence of tissue composition on uptake of NH4+, NO3− and PO43‐ by Enteromorpha prolifera (Müller) J. Agardh was examined. For NH4+ uptake, Vmax was 188 μmol NH4+. g dry wt−1. h−1 and Ks ranged from 9.3 to 13.4 μM, but there was no correlation between kinetic parameters and tissue nitrogen content. For NO3−, both kinetic parameters were higher for plants with low tissue nitrogen than for plants with high tissue nitrogen. Maximum rates were 169 and 75.4 μmol NO3−. g dry wt−1. h−1, and Ks was 13.3 and 2.31 μM for low and high tissue nitrogen plants, respectively. Estimates of uptake in the field suggested that NH4+ accounted for 65% and NO3− for up to 35% of total nitrogen uptake during the summer. Nutrient uptake rates of field‐collected plants also indicated that E. prolifera in Yaquina Bay, Oregon was not likely to have been nitrogen‐limited, but may have been phosphorus‐limited.