Physiological differences between the nutrient uptakes of Kjellmaniella crassifolia and Laminaria japonica (Phaeophyceae)

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The nutrient uptake kinetics of Kjellmaniella crassifolia and Laminaria japonica were determined under a variety of conditions. The nitrate and phosphate uptake rates followed Michaelis-Menten kinetics toward ambient nutrient concentrations, showing no difference between the maximum uptake rates of the two species. However, half-saturations of nitrate and phosphate uptake kinetics in K. crassifolia were higher than those in L. japonica. Low water temperature (5°C) greatly restrained the nitrate and phosphate uptakes of both algae. Low irradiance (< 100 μE/m² per s) restrained nitrate and phosphate uptakes only in L. japonica, although high irradiance (> 100 μE/m² per s) caused no difference between the two species. The nitrate and phosphate uptake rates at low irradiance in K. crassifolia were 2-7 times higher than those in L. japonica. Light compensation and saturation irradiances in K. crassifolia were significantly lower than in L. japonica. These results indicate that K. crassifolia is able to take up carbon and nutrients at low irradiance, which suggests that the nutrient uptake characteristic of K. crassifolia could allow it to adapt to deeper habitats and even to high water turbidity.