Changes of Growth and Nutrient-relating Enzymatic Activities of Sargassum thunbergii When Exposed to Different Nutrient Conditions

Abstract

Macroalgae have been suggested to play an important role in seawater decontamination. It is reported that Sargassum thunbergii has been one of the dominant macroalgal species of the intertidal zone along the coastal Shandong Province. However, serious degradation has occurred because of the pollution and the deterioration of seawater quality. The purpose of the present study was to study the growth changes of S. thunbergii when exposed to different nutrient conditions, and the possible effective mechanism basing on nutrient-relating enzymatic activity was studied. Result showed that: (1) The relative growth rate (RGR) of S. thunbergiiis varied greatly when exposed to different nutrient conditions, and its fresh weight in the treated group was significantly inhibited as compared to that in the control. It seemed that high concentration of phosphate had more obviously inhibitory effect on growth of S. thunbergii as compared to the effect of nitrate changes. Moreover, the concentrations of phosphate and nitrate fluctuated with time and concentration increasing, inferring the mechanism of absorption and release might co-existe in S. thunbergii. (2) The activity of Nitrate reductase (NR) increased with the increment of the environmental nitrate concentration, but relatively higher N:P ration (32:1) significantly inhibited its activity. Alkaline Phosphatase (AKP) increased with the increment of the environmental phosphate concentration in groups of 0 and 2.5µmol/L, but decreased adversely with concentration increment in groups of 16µmol/L and 80µmol/L. Results in the present study demonstrated a significant effect of environmental nutrient conditions on growth of S. thunbergiiis and a co-existent mechanism of absorption and release of nitrate and phosphate was suggested in S. thunbergiiis.