Influence of the concentration ratio of nitrogen to phosphorus on the growth and interspecies competition of two red tide algae

The growth and interspecies competition of two red tide algal species Thalassiosira pseudonana Hasle et Heimdal and Gymnodinium sp. were studied under different concentration ratios of nitrogen to phosphorus, and the algal hatch culture experiments were conducted. The physiological and biochemical indexes were measured periodically, including the maximum comparing growth rate, relative growth rate, average double time and chlorophyll a concentration. The results showed that when the concentration ratio of nitrogen to phosphorus was 16： 1, the maximum comparing growth rate, relative growth rate and chlorophyll a concentration of Thalassiosira pseudonana all reached the highest,and average double time was the shortest. This implied that the optimal concentration ratio of nitrogen to phosphorus of Thalassiosira pseudonana is 16： 1. When the concentration ratio of nitrogen to phosphorus was 6：1, the maximum comparing growth rate, relative growth rate and the chlorophyll a concentration of Gymnodinium sp. reached the highest, and average double time was the shortest, so the optimal concentration ratio of nitrogen to phosphorus of Gymnodinium sp. is 6： 1. From the growth curves as indicated both in the cell density and the chlorophyll a concentration, it is suggested that the influence of concentration ratio of nitrogen to phosphorus on the chlorophyll a concentration and the cell density are almost the same. Different concentration ratios of nitrogen to phosphorus had weak influence on community succession and the competition between the two algae. Gymnodinium sp. may use the phosphorus in vivo for growth, so it is important to pay attention to the concealment of phosphorus, in order to avoid the outbreak of red tide. On the basis of the importance of nitrogen and phosphorus and the ratio of their concentration, the possible outbreak mechanism of red tide of the two algae was also discussed.

Influences of Nitrogen-phosphorus Ratio on the Growth and Competition of Chlorella vulga and Anabaena sp. strain PCC

This paper studied the effects of different ratios of nitrogen and phospho- rus on the growth and competition of Anabaena sp. strain PCC and chloralla vul- gads （low nitrogen-phosphorus ratio group： N/P=16：1; Medium low nitrogen-phospho- rus ratio group： N/P=32：1; Medium high nitrogen-phosphorus ratio group： N/P=64：1; High nitrogen-phosphorus ratio group： N/P=320：1）. Results suggested that the largest amount of anabaena sp.strain PCC survived in medium high nitrogen-phosphorus ratio group. The nitrogen-phosphorus ratio showed no significant influences on the growth of Chlorella vulgaris, but it exerted dramatic influences on the growth of Chlore/la vulgaris of the mixed cultivation system. The largest amount of Ch/orel/a vulgaris can be found in the medium-high nitrogen-phosphorus ratio group. The inhi- bition parameter of nitrogen-phosphorus on the algae was distinctive. Anabaena sp. strain PCC had advantages in the competition with the low nitrogen-phosphorus ra- tio and medium-low nitrogen-phosphorus ratio. Potential instability existed between anabaena sp.strain PCC and Chlorella vulgaris when the nitrogen to phosphorus ratio was medium-high and high.

Characterization of the Growth,Chlorophyll Content and Lipid Accumulation in a Marine Microalgae Dunaliella tertiolecta under Different Nitrogen to Phosphorus Ratios

Microalgal lipids are regarded as main future feedstock of biofuels for its higher efficiency of accumulation and sus- tainable production. In order to investigate the effect of various nitrogen to phosphorus ratios on cells growth, chlorophyll content and accumulation of lipids in Dunaliella tertiolecta, experiments were carried out in modified microalgal medium with inorganic nitrogen （nitrate-nitrogen） or organic nitrogen （urea-nitrogen） as the sole nitrogen source at initial N：P ratios ranging from 1：1 to 32：1. The favorable N：P of 16：1 in the nitrate-N or urea-N medium yielded the maximum cell density and specific growth rate. Decrease in chlorophyll content were observed at the N：P of 4：1 in both nitrate-N and urea-N cultures. It was also observed that the maximum lipids concentration was obtained at the N：P of 4：1 in both nitrate and urea nutrient medium. The lipid productivity and lipid content of cultures in the urea-N medium at the N：P of 4： lwere markedly higher than those from cultures with other N：P ratios （p〈 0.05）. The results of this work illustrate the possibility that higher ratios of nitrogen to phosphorus have enhancing effect on cells growth of D. tertiolecta. Conversely, higher lipid accumulation is associated with a decrease in chlorophyll content under lower ratios of nitro- gen to phosphorus. The results confirm the hypothesis of this study that a larger metabolic flux has been channeled to lipid accumu- lation in D. tertiolecta cells when the ratios of nitrogen to phosphorus drop below a critical level.