Physiological and biochemical response of seaweed Gracilaria lemaneiformis to concentration changes of N and P

This paper presents the studies of nitrogen and phosphorus (N/P) concentrations influence on the antioxidantivity of Gracilaria lemaneiformis and the physio-chemical features in an indoor seawater culture system. The results showed that the specific growth rate, the chemical composition (concentrations of chlorophyll a, phycoerythrin and soluble protein), nitrate reductase activity, antioxidantive defense system (the activities of superoxide dismutase, peroxidase, catalase) and propyldialdehyde content of G. lemaneiformis were affected by changes in concentrations of N and P, and in seaweed culture time. G. lemaneiformis showed increased growth rate when the N/P concentrations increased from 50/3.13 µmol/L to 400/25 µmol/L. But when the N/P concentrations exceeded 400/25 µmol/L, the growth rate dropped significantly. The trend became more obvious once the N/P concentrations reached 600 / 37.5 µmol/L. At these concentrations, the chloroplasts in G. lemaneiformis were damaged as evidences that 1) the number of thylakoids was increased, some of them were swollen up, irregularly aligned, ruptured and partly dissolved; 2) the chloroplast volume was increased; and 3) starch grains in chloroplasts accumulated significantly. On the basis of these results, a remediation critical point for the growth of G. lemaneiformis under high N/P concentrations was proposed.