| Abstract: | The effect of phosphate (Pi) supply on growth rate and tissue phosphorus content of juvenile Macrocystis pyrifera (L.) C. Ag. sporophytes was examined. Sporophytes were batch cultured in aquaria with flowing recirculated seawater enriched by 30 μM nitrate. Each aquarium was supplemented with a different seawater Pi concentration, 0, 0.3, 1, 2, 3, and 6 μM. Sporophyte mean specific growth rates declined with time in all cultures presumably due to the normal developmental decrease in the proportion of meristematic tissue of each plant. Growth rate declines were more pronounced in cultures that were nutrient limited. Sporophyte growth was P-limited after two-week exposure to Pi less than 1 μM, corresponding to a tissue P concentration of less than 0.20% dry weight. Plants cultured at 6 μM Pi contained tissue P levels of 0.53% dry weight after three weeks. Luxury consumption and storage of P occurred. |
