EFFECT OF NITROGEN SUPPLY ON NITROGEN CONTENT AND GROWTH RATE OF JUVENILE MACROCYSTIS PYRIFERA (PHAEOPHYTA) SPOROPHYTES1

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Abstract
The effect of nitrogen supply on nitrogen content and growth rate of juvenile Macrocystis pyrifera (L.) C. A. Agardh sporophytes was studied in two types of experiments: growth in continuously flowing mixtures of deep (nutrient‐rich) and surface (nutrient‐poor) seawater, and growth in batch cultures with alternate 7–10 day periods in deep and surface water. In the continuous flow experiments, the nitrogen content of the plants increased with the increased concentration of nitrate in the seawater. In the batch culture experiments, a lag period of 3–7 days often occurred before changes in the nitrogen supply were reflected in corresponding changes in the nitrogen content of the plants. Growth rates were a linear function of tissue nitrogen which varied between 1–3% dry weight. Saturation of growth rate as a function of tissue nitrogen did not occur, although tissue nitrogen levels did saturate as a function of external nitrate supply. Juvenile M. pyrifera sporophytes do not appear to “store” nitrogen. Total nitrogen varies from 1–6% dry weight in Laminariales and Fucales, but only some species of Laminaria appear to accumulate large pools of “surplus” nitrogen.