The influence of macronitrogen (NO₃^- and NH₄⁺) addition with Ulva pertusa on dissolved inorganic carbon system

The influence of macronitrogen (NO₃^- and NH₄⁺) addition with Ulva pertusa on dissolved inorganic carbon system in seawater was studied. The results indicate that p (CO₂) and HCO₃^- concentration decrease significantly, while pH and CO₃^2- concentration increase significantly. When the concentration of NO₃^- was less than 71 μmol/dm³ or NH₄⁺ was less than 49.7 μmol/dm³, dissolved inorganic carbon (DIC) absorption rates by Ulva pertusa generally increased with the increasing of nitrogen concentration. The DIC decreased 151 μmol/dm³ with the addition of 71 μmol/dm³ NO₃^- and decreased 232 μmol/dm³ with the addition of 49.7 μmol/dm³ NH₄⁺ after the experiment compared with DIC measured without nitrogen addition. A significant negative-correlation was found between △c (DIC) and growth rate (μ) of Ulva pertusa (r=-0.91, P <0.000 1, n=11). NH₄⁺ had more influence on the species of inorganic carbon system than NO₃^-.