| The growth of stoylo, an exotic tropical leguminous pasture species, has been shown to cause soil acidification, which has handicapped the crop for further expansion in China and other tropical countries. Phosphorus deficiency is believed to be an important factor for the soil acidification in association with the growing of the stoylo. Therefore enhancement of efficiency of phosphorus use by the crop is expected to relieve the problem of soil acidification with the aid of soil microorganisms with phosphorus-dissolving ability. It is on this context that the present study tried to look for such microorganisms and test them through pot culture of stylosanthes spp. to see the acidification-relieving effects.We have successfully isolated 75 bacteria strains from Stylosanthes guianensis Reyan No.2, Stylosanthes. guianensis cv. Reyan No. 5, Stylosanthes scabra cv. Seca, Stylosanthes hamat, Paspalum Longifolium, Panicum maximum cv. Reyan No. 8, Panicum maximum cv. Reyan No.9, Brachiarai decumbens Reyan No.3, and Brachiaria decumbens cv.hybrid, and mangrove rhizosphere, including 36 inorganic phosphobacteria and 52 organic phosphobacteria. The ensuing screenings of the bacterial strains through observation of size of phosphorus-solubilizing cultures on plate and submerged cultures with shake flask was rewarded with some most promising strains with best phosphorus dissolving efficiency, i.e., GI2-6 {Bacillus spp), GI9-4-2( Bacillus spp), GI 9-4-3(Serratia spp) and GI 8-5-2(Enterobacter spp) from stylo rhizosphere for inorganic phosphorus, and Mo 1-4-3 (Pantoea spp) and Mo4-5-l( Chryseomonas spp) from mangrove rhizosphere for organic phosphorus.To determine the optimal culture media and phosphorus-dissolving conditions, the strain GI 2-6( Bacillus spp.) and GI 9-4-3( Serratia spp) were used. We found that their growth and Ca3(PO4)2-dissolving ability of the GI 2-6( Bacillus spp.) and GI 9-4-3( Serratia spp) were different under the condition of different carbon source, nitrogen source, pH level, and temperature, and that their growth was positively correlated with their phosphorus-dissolving performance. For GI 2-6( Bacillus spp.), the optimal carbon and nitrogen source were sucrose at the concentration of 5.0 g/1, KNO3 at the concentration of 1.5 g/1, with pH at 7.0 and temperature at 28°C; while for GI 9-4-3( Serratia spp) the optimal carbon and nitrogen source were glucose at the concentration of 5.0g/l and KNO3 at 1.5 g/1 with pH at 9.5 and temperature at 32°C. The importance of the four factors are ranked in decreasing order: nitrogen source > carbon source>temperature > pH in the case of GI 2-6( Bacillus spp.) and temperature > carbon source > nitrogen source > pH in the case of GI 9-4-3( Serratia spp).Pot culture experiment made with inoculation of the inorganic phosphobacteria GI 2-6( Bacillus spp.) and GI 9-4-3( Serratia spp) to the Stylosanthes guianensis Reyan No.2 and Stylosanthes hamat indicated that the GI 2-6( Bacillus spp.) and GI 9-4-3( Serratia spp) improved the growth and P content of the two stoylo cultivars, as well as the available phosphorus of rhizosphere and the quantity of soil microorganisms of Stylosanthes guianensis Reyan II and Stylosanthes hamat. Comparatively GI 2-6( Bacillus spp.) was somewhat better than GI 9-4-3( Serratia spp). Lower phosphorus level was also better than higher P level at stimulating the growth of the plants, the P accumulation in the plants and the avaible phosphorus of rhizosphere. GI 2-6( Bacillus spp.) and GI 9-4-3( Serratia spp) lifted the pH of the stoylo rhizosphere to certain extent, particularly at lower P level, indicating that P stress is favorable for the bacteria to relieve the soil acidification problem from stylosanthes spp. growing.It is concluded that soil...
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