Effect of nutrient supply on nitrogen and phosphorus uptake and growth in three species of macroalgae

We conducted a series of conditional experiments using Gracilaria asiatica,G.chouae,and Grateloupia filicina to determine the effects of nutrient supply on nitrogen and phosphorus uptake and macroalgae growth.All the three macroalgae responded rapidly to changes in the supply of nitrogen and phosphorus.The uptake curves yielded a first-order kinetic equation.At 50 μmol/L nitrogen,G.asiatica and G.chouae exhibited maximum uptake rates of 0.739 μmol/(g·h) and 0.648 μmol/(g·h) respectively.At 20 μmol/L nitrogen,G.filicina exhibited a maxi-mum uptake rate of 0.614 μmol/(g·h).At a level of 1.0 μmol/L phosphorus,G.asiatica and G.chouae exhibited maximum uptake rates of 0.015 μmol/(g·h) and 0.018 μmol/(g·h),respectively.At 0.7 μmol/L phosphorus,G.filicina exhibited a maximum uptake rate of 0.016 μmol/(g·h).Our results suggest that G.chouae is more efficient at removing nitrogen and phosphorus than the other two species.The greatest increase in wet weight occurred in G.chouae and the lowest was in G.filicina.Changes in the supply of nitrogen had a stronger influence than changes in phosphorus on the growth of G.filicina.