Fundamental Research On Phosphate-solubilizing Microorganisms From The Rhizosphere Of Betel Nuts (Areca Catechu) And The Preparation Of PSM-containing Biofertilizers

The natural availability of phosphorus (P) is very low in ecosystems, particularlyin tropical soils. After applying phosphate-based fertilizers to tropical acidic soils,precipitation induced by aluminum is the major cause of P fixation. In this study, therhizosphere and bulk soils of Areca catechu plants were sampled separately in theseven important production areas on Hainan Island. The research studied thedistribution of phosphate-solubilizing bacteria (PSB) in soils, measured theperformance of phosphate solubilization and investigated the mechanism of insolublephosphate solubilization by microorganism. A total of929PSB isolates werecollected from the rhizosphere and bulk soils. This is the first time to demonstrate thatAcinetobacter pittii and Talaromyces flavus are promising phosphate-solubilizingmicroorganisms．Results showed that the number of PSB was negatively correlated(P <0.0001) with the available P content and positively correlated (P <0.0002) withexchangeable Al concentrations of soil.Their ability to solubilize insoluble phosphatewere significantly greater (P <0.0001) in soils with low available phosphorus (P)content than in other soil types. Three PSB strains (ASL12, ASG34, and ADH302)and two phosphate-solubilizing fungi (PSF) strains (ADH301and ADH1026)demonstrated the capacity of solubilizing aluminum phosphate and iron phosphate.These five strains also showed resistance against different environmental stresses,such as a pH range from3to9and a temperature range from10°C to50°C. Anincrease of Cu immobilization by30.6%was observed for fungal strain ADH301andthat by43.9%for ADH1026. HPLC analysis of the culture filtrates was performedand the result indicates the presence of eight kinds of organic acid during thesolubilization of TCP. Among these acids, gluconic acid was produced in highamounts (7862.4μgml1) and thus led to a drop of the pH. An inverse correlation(r=0.758, P≤0.01) was observed between the final pH in the culture and the quantityof released P.ADH1026exhibited significant solubilization of rock phosphate (RP) usingcarboxymethyl cellulose (CMC) as sole carbon sources. Therefore, this research alsostudied biofertilizers preparation using middle-low grade RP and coconut shell byPSF ADH1026and the efficient cellulose degradation strain RPW3. The optimumconditions for the fungal strain of ADH1026to solubilize middle-low grade RP were studied: culture time,8-9d; initial pH,5-6; culture temperature，30-35℃；inoculationvolume,25%; shaking speed190rpm; RP concentration3g L1; C/N ratio,30. Bypretreating coconut shell with alkali (2%NaOH,80°C,80min), cellulose conversionrate reached88.4%,87.8%and87.7%, respectively.An efficient cellulose degradationstrain, RPW3, was isolated from red plam weevil larva. RPW3and ADH1026weremixed culture using alkali pretreated coconut shell as carbon sources and RP as the Psource. The soluble P concentration in the culture reached218.3mg L1.This study also investigated the seedling growth of Areca catechu promoted bythree PSB isolates and two PSF in pot experiments. A high (P<0.05) correlation wasobserved between P-solubilization activity and A. catechu plant growth. In thepresence of aluminum phosphate, an increase of35.7%、17.9%、14.3%and39.3%,respectively, in P contents of leaves was recorded in the inoculated ASL12、ASG34、ADH302and the mixed inoculation with the three PSB compared with theuninoculated treatments. In the presence of RP, an increase of7.4%、22.2%and33.3%, respectively, in P contents of leaves was recorded in the inoculated ADH301,ADH1026and the combined inoculation with the two PSF compared with theuninoculated treatments.In conclusion, the five strains studied in this research demonstrated excellentcapacities of P solubilization and can be potentially applied as inoculants to increasesoluble phosphorus in tropical and aluminum-rich soils.