| Oocystis borgei is dominant algae with the characteristics of wild distribution, stable population and high flexibility in breeding mid-late shrimp pond, it plays an important role in regulating water quality. In this paper the variation of dissolved inorganic nitrogen (nitrate, nitrite and ammonium) and inorganic phosphorus content as well as water temperature and dissolved oxygen were determined in three intensive aquaculture ponds of Litopenaeus vannamei in the East Island of Zhanjiang from April to July, 2010. At the same time the uptake of inorganic nitrogen by Oocystis borgei was also studied under different nitrogen concentration, algae concentration, temperature, seawater density and illumination intensity. All these are in order to provide theoretical basis of biological control water quality. Experimental results are as follows:1,During breeding the content of ammonium nitrogen was high both in prophase and anaphasis, and low in metaphase, ranging from 0.011 to 0.882mg·L-1, with the average of 0.155mg·L-1. Nitrite concentration was stable in prophase and metaphase, while higher in anaphasis, was in the range of 0.0050.103 mg·L-1, with the average of 0.020 mg·L-1. As for the nitrate content, it had a relatively large fluctuation,varying from 0.001 mg·L-1 to 0.811 mg·L-1,with the average of 0.193 mg·L-1. So we suggest that we should choose the algae with stable and long growth cycle to put in ponds during breeding.2,The content of inorganic nitrogen varied from 0.040 to 1.294 mg·L-1, with average of 0.368 mg·L-1. There was not an significant change in inorganic phosphorus content, ranging from 0.019 to 0.235 mg·L-1, an average of 0.066 mg·L-1, the eutrophication of water body was severe.3,Rate of IN/IP varied from 0.474 to 20.575 during breeding, with the average of 5.984, of which period lesser than five acounted 48%. IN is the factor that limited the growth of planktonic.4,Water temperature was low in prophase but increased in metaphase and anaphasis during breeding varying from 22.54to 31.48℃, in prophase temperature was low and changed sharply and kept 3 months when it was at 30℃. We suggest that culturing seedings after April.5,Dissolved oxygen was in the range of 5.049.88 mg·L-1, was high in prophase and low in anaphasis during breeding. So we should increase oxygen conveyed in anaphasis.6,There was a significant influence on the uptake of nitrogen by Oocystis borgei under different density of nitrate, nitrite and ammonium, with P<0.05. When pure nitrogen concentration of nitrate, nitrite and ammonium was 14.300 mg·L-1, uptakes of nitrate, nitrite and ammonium by algae all reached the highest were 73.173ug·g-1·h-1, 95.872ug·g-1·h-1 and 52.259 ug·g-1·h-1 respectively. When pure nitrogen concentration of nitrate and nitrite was 3.300 mg·L-1, uptakes of nitrate and nitrite by algae all dropped to the lowest were 42.161ug·g-1·h-1 and 24.252ug·g-1·h-1 respectively. For uptake rate of ammonium, when pure nitrogen concentration of ammonium was 96.800 mg·L-1, the rate was the lowest, was 20.856 ug·g-1·h-1. Thus both low and high nitrogen concent would decrease the uptake of inorganic nitrogen by algae.7,There was a significant influence on the rate of three nitrogen resourses uptake under diverse algae concentration with P < 0.05. When algae density was 3.222×108cell·L-1,uptakes of nitrate and nitrite reached the highest were 9.767 ug·g-1·h-1 and 6.912 ug·g-1·h-1 respectively. For ammonium, the uptake got to top 58.803 ug·g-1·h-1 as algae density was 4.784×108cell·L-1. When algae density was 9.472×108cell·L-1, uptakes of three kinds of nitrogen dropped to the lowest were 2.502 ug·g-1·h-1, 3.421 ug·g-1·h-1 and 31.833 ug·g-1·h-1 respectively. Thus over high density algae would reduce nitrogen uptake.8,The effect of temperature on the uptake of three kinds of nitrogen source was significant obvious with P<0.05. When temperature was at 30℃, the uptake of nitrate, nitrite and ammonium by algae all reached the top were 48.130 ug·g-1·h-1, 27.421 ug·g-1·h-1 and 51.929 ug·g-1·h-1 respectively, while when temperature was at 10℃, uptake of nitrate, nitrite and ammonium all dropped to the lowest were 12.904 ug·g-1·h-1, 13.817 ug·g-1·h-1 and 29.072ug·g-1·h-1 respectively. Therefore Oocystis borgei grew better in higher temperature, low temperature was not benefit for taking nitrogen.9,The effect of seawater density on the uptake of three nitrogen sources was significant obvious, too, with P<0.05. Uptake of nitrate, nitrite and ammonium by Oocystis borgei got to the highest when seawater relative density was at 1.010 g·mL-1, were 14.501ug·g-1·h-1, 16.357ug·g-1·h-1 and 65.420ug·g-1·h-1 respectively, the lowest uptake of nitrate and ammonium were 8.305 ug·g-1·h-1 and 38.415 ug·g-1·h-1 as density was at 1.030g/ml, and the lowest uptake of nitrite was 11.279ug·g-1·h-1 as density was at 1.005g/ml. Therefore over high seawater density would reduce nitrogen uptake.10,The effect of illumination on the uptake of three nitrogen sources was also remarkeble with P<0.05. Uptake of nitrate, nitrite and ammonium by Oocystis borgei got to the highest when illumination was 45μmol·m-2·s-1, were 11.100ug·g-1·h-1, 15.340ug·g-1·h-1 and 14.077ug·g-1·h-1 respectively, the lowest uptake of nitrate, nitrite and ammonium were 2.502ug·g-1·h-1, 2.355ug·g-1·h-1 and 3.618ug·g-1·h-1 as illumination was 153μmol·m-2·s-1. Thus high light would decrease the uptake of nitrogen by algae. |
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