Diversity Of Phosphorus Solubilizing Bacteria In Citrus Orchard Soil And Their Effects On The Plant Growth Of Poncirus Trifoliata L.

Phosphorus(P)is the most important nutrient element for plant growth after nitrogen.It is a component of key molecules in plants and participates in the physiological metabolism of plants,and P difficiency limits the growth and development of plants.The soil has a high content of total P,however,the available P content that plants can directly utillize is very low.Due to its special physical characteristics and environmental factors,the red soil in southern China has characteristics of poor availability of residual P,low utilization rate of P fertilizer,and tendency to be fixed.Studies have found that soil P solubilizing bacteria(PSB)can solubilize poorly soluble P and promote plant uptake.In this study,we separated,screened and identified PSB from the red soil of southern citrus orchard,and the pot experiment was carried out to evaluate the growth-promoting effect of PSB on citrus plants.The main results were as follows:(1)According to the presence of P solubilizing halo,127 PSB stains were isolated and purified from red soil of citrus orchard.During the colony morphology observation and 16S r DNA identification,we obtained 52 PSB strains,belonging to 20 genera,of which 9species belong to Streptomyces.Cluster analysis showed that 52 PSB strains belong to Actinobacteria,Firmicutes and Proteobacteria.These results indicate the abundant and diverse PSB resource in citrus orchard soil.(2)The liquid and solid media of poorly soluble P were used to determine the P solubilizing ability of 52 strains.It was found that strain P18 had the highest D/d in the Fe PO₄·2H₂O solid medium,which was 4.98.Strain P5 had the strongest ability to dissolve P in Ca₃(PO₄)₂ liquid medium,which was 244.28 mg/L.In the liquid medium of poorly soluble inorganic P,the amount of dissolved P was negatively correlated with the final p H,confirming that p H is the important factor affecting the solubilization of pooly soluble P.(3)Pot experiment showed that the addition of P fertilizer promoted the root's growth and the plant P uptake,however,the inoculation of PSB significantly reduced the biomass of the plant,which is probably related to the microbial competition for P.(4)PSB inoculation,phosphorus addition and their interaction significantly increased soil available phosphorus.PSB inoculation and phosphorus addition significantly promoted the mineralization of soil-mineralized organic phosphorus.(5)PSB inoculation and interaction between PSB inoculation and phosphorus addition significantly increased soil bacterial abundance.PSB inoculation and phosphorus addition increased the abundance of soil phosphorus recycling functional genes and significantly affected soil bacterial community structure.