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Annual growth per plant and allocation of growth to the stipe were measured in 2- to 4-year-old plants of Laminaria hyperborea from five stations with different degrees of wave exposure and different amounts of canopy biomass. Low growth in plants with initial stipe lengths of less than about 40 cm suggested that the presence of canopy-forming plants suppresses growth of understorey plants, and this was supported by the high lamina growth rate of understorey plants after removal of the canopy-forming plants. Canopy biomass and wave exposure were found to exert a differential effect on the growth of the age groups examined. Average annual growth per plant in 2- to 3- year-old plants decreased with increasing canopy biomass; growth of 4 year-old plants was not significantly influenced by canopy biomass, but increased with increasing wave exposure of the sites, suggesting an influence of some factor connected with wave exposure. The allocation of annual growth to stipe and lamina was also found to be influen...

Lamina elongation and content of mannitol, laminaran and nitrate were measured during one year in Laminaria saccharina sensu lato from Iceland. The population contained both solid- and hollow-stiped plants. Growth rate was at its minimum from October to December, and started to increase in mid-winter, slightly earlier at 3 m than at 5 m. The increase in growth rate coincided with a strong reduction in stored carbohydrates and an increase in nitrate content of the laminae, indicating that stored mannitol and laminaran provided extra energy for increased lamina growth and/or for nitrate uptake. The results showed that stored mannitol was utilised before laminaran. The growth rate was at its maximum from April to June, and was reduced from June to July. The ambient nitrate concentration at the locality was low from May to August. The nitrate content of the lamina tissue in relation to dry weight was high during spring but was reduced to low values by July, indicating that nitrate levels limited growth during...