Isolation Of Phosphate Solubilizing Microorganisms And Their Efficiency Differences In Solubilizing Various Insoluble Phosphates

Phosphorus is one of the essential macronutrients for plants growth. In China, nearly 75% of soils are deficient in available phosphorus. So amounts of chemical P fertilizers were added into soils every year. Phosphate solubilizing microorganisms (PSMs) are proved to play an important role in releasing P from inorganic and organic pools of total soil P through solubilization and mineralization. Soil PSMs applications can greatly reduce the use of chemical fertilizers, and promote the development of the sustainable agriculture. The purpose of this work was to isolate PSMs with high efficiency in solubilizing hardly soluble phosphates from soils of different land use types in Changsha and Changde, China. Impacts of various conditions (carbon resources, nitrogen resources, pH and salinity) to the growth and phosphate solubilizing efficiency (PSE) of fungi Al and P1, and the relationships between phosphate solubilization with fungal biomass and medium pH variation were investigated aiming to supply some theoretical bases and technical supports for the practical applications of PSMs in future. The results are as follows:(1) Eight bacteria and two fungi strains were harvested by plate screening methods from different soils. After quantitative estimation of efficiency to solubilizing Ca2(PO4)3 in liquid Pikovskaya (PVK) medium, two fungi strains A1 and P1 were selected as the objects studied in the later period. A1 and P1 were preliminarily identified to Aspergillus spp. and Penicillium spp. respectively by morphological observation.(2) Different carbon, nitrogen resources, salinity and pH had obvious impacts on the growth and PSE of A1 and P1. The biomass and soluble P content in PVK medium inoculated with A1 were remarkably different among four carbon resources. A1 could utilize maltose by the greatest extent, while the biomass and PSE when sucrose as carbon resource were both lower obviously than maltose and glucose. A1 could not utilize starch as carbon resource, so the growth and PSE were both zero. Different carbon types had little effects on P1's growth and PSE. Ammonia was more efficient in promoting the PSE of A1 and P1 compared with nitrate, even though the biomass when nitrate existed were higher than ammonia.(3) Both strains had strong ability to tolerate high NaCl concentration. A1 could survive in salinity 10% while P1 only could live below salinity 8%. Both of A1 and P1 could grow normally in acid circumstance, and A1 grew better in strong acid situation than P1. However, A1 could hardly grow in alkaline situation. The biomass of P1 reached to maximum when pH 8. At pH 10, P1 still survived while A1 could not.(4) The solubilizing efficiency to four inorganic phosphate compounds of A1 and P1 were significantly different. Both of them had strong solubilizing effect to Ca3(PO4)2 and AIPO4 compared with rock phosphate and FePO4. P1 had no solubilizing ability to FePO4. The order of highest solubilization efficiency to four different inorganic phosphates of A1 was Ca3(PO4)2(89%)>AlPO4(85%)>PR(28%)> FePO4(19%). The order of P1 was the same with A1, while its PSE was 93%,77%,37% and 0 respectively. With the concentration of soluble P increased, all the PVK medium inoculated with A1 or P1 accompanied with pH drop and biomass increase. Except the process of P1's solubilization to FePO4, the other processes were all significantly correlated with the fungal biomass and pH drop of the medium.(5) Both A1 and P1 could mineralize organic phosphate (Calcium phosphate) to soluble P in liquid culture, and the soluble P concentration was about 250 mg/L. In the mineralization process, both of them could produce phosphatases. The activities of acid phosphatases were significantly higher than alkaline phosphatase. The final pH of the PVK medium inoculated with A1 or P1 were much lower than CK (not inoculated any strains), even than the inorganic phosphates medium.