Biochemical and uptake responses of the macroalga Gracilaria lemaneiformis under urea enrichment conditions
2017
Han, Tingting | Qi, Zhanhui | Huang, Honghui | Fu, Guiquan
Thallus growth, nutrient uptake characteristics, and biochemical composition of Gracilaria lemaneiformis cultured at different urea concentrations of 5, 10, 25, 50, 100, 200, and 400μM nitrogen (N) were analyzed. Urea uptake revealed two distinct patterns: a rate-unsaturated uptake kinetic for N-limited thalli and a rate-saturating uptake kinetic (Vmax=27.46±1.24μmolNg−1DWh−1 and Ks=95.81±11.65μMN) for N-replete thalli. Urea uptake rate in both N-limited and N-replete G. lemaneiformis increased with elevated urea concentration, and was largely enhanced in N-limited thalli relative to N-replete thalli. The relationship between tissue total nitrogen (TN) content and growth rate was not always linear for G. lemaneiformis. There was a significant increase in tissue TN content from the control value of 0.93%–>2.5% dry weight at high (≥100μMN) urea concentrations, and the highest growth rate was detected at 100μMN. The content of photosynthetic pigments Chlorophyll a and Phycoerythrin increased with tissue TN up to 100μMN but decreased at higher urea concentrations. However, only minor differences in the content of soluble protein as a percentage of tissue TN were observed. The results of the present study indicate that urea uptake by G. lemaneiformis in the field (where urea concentration is <25μMN) is directed towards increased growth and N storage.
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