Survey On Phosphorus Content In Litopenaeus Vannamei's Culture Ponds And Preliminary Study On Phosphate Solubilizing Bacteria

Changes of nitrogen and phosphorous nutrients in Litopenaeus vannamei's semi-intensive culture ponds in estuary were investigated in the Pearl River Delta from September 2007 to February 2008. The results showed that dissolved inorganic phosphorus (DIP) in the ponds were lower, and the excess of dissolved inorganic nitrogen (DIN) mainly resulted to potential eutrophication. The water in the ponds was mostly in the state of potential eutrophication with medium limited phosphorous and potential eutrophication with limited phosphorous. Contents of total phosphorus (TP) in sediment of shrimp ponds were high, and accumulated significant.Contents of phosphorus and amounts of phosphate solubilizing bacteria (PSB) in water and sediment of Litopenaeus vannamei's ponds were investigated from July to December 2009 in four kinds of culture patterns. They were semi-intensive culture ponds in tidal flat (SICP-T), semi-intensive culture ponds in estuary (SICP-E), intensive culture ponds in high tide zone (ICP-H) and poly-culture ponds in tidal flat (PCP-T). The results showed that contents of DIP stayed at a low level in water of SICP-T, SICP-E and PCP-T. And the averages of DIP in these three kinds of shrimp ponds were<0.010 mg/L,0.017±0.004 mg/L and 0.017±0.006 mg/L, respectively. The contents of DIP in surface and bottom of ICP-H were significantly higher than the other three types of ponds (P＜0.05). The averages of TP in sediment of SICP-T, SICP-E and PCP-T were 506±169 mg/kg, 1049±96 mg/kg and 660±56 mg/kg, respectively. The detectable rates of PSB were low in water and sediment of SICP-T and SICP-E. The amounts of PSB in water and sediment of PCP-T were higher than other kinds of culture ponds, and ICP-H followed. But the ratios of PSB to heterotrophic bacteria were at a very low level.Four strains of PSB were isolated. Using 16S rDNA sequence analysis and BIOLOG identification, these four strains g6, y8, d4 and D11 were identified as Pantoea stewartii subsp. stewartii, Burkholderia cepacia, Klebsiella pneumoniae subsp. pneumoniae and Acinetobacter calcoaceticus/genospecies 3, respectively.Effects of temperature, salinity and initial pH on three strains'growth were studied. The results showed that P. stewartii subsp. stewartii g6 grew at all the temperature tested, and grew especially well in the range of 25～35℃. It could tolerate a wider salinity range from 5 to 35, and grew well in initial pH of 6 to 10. A. calcoaceticus/genospecies 3 D11 could tolerate a wider range of temperature, salinity and initial pH such as temperature (25 ～35℃), salinity (10～25), and initial pH (6～10). And B. cepacia y8 had a relatively narrow scope of adaptation comparing with the other two strains. In general, the present environmental conditions of culture ponds were suitable for the growth of these PSB strains.