Mechanism Of Phosphorus Solubilization By Phosphorus-Dissolving Bacteria And Its Effect On The Growth Of Rice Under Phosphorus Deficiency Conditions

Our arable soils are characterised by high levels of total phosphorus and a lack of effective phosphorus.The lack of effective phosphorus in the soil not only restricts the growth of plants,but also affects agricultural development.The application of phosphorus fertilisers has significantly improved the deficiency of effective phosphorus in soils and increased the growth and yield of crops,but on the one hand,phosphorus fertilisers are non-renewable resources and their continuous application is not sustainable.On the other hand,excessive application of phosphate fertiliser may lead to eutrophication of water bodies and soil consolidation.The use of phosphate solubilising microorganisms to convert phosphate in the insoluble state in soil into effective phosphorus that can be directly absorbed and utilised by plants,thereby improving the uptake and utilisation efficiency of phosphate fertilisation by crops,is a popular direction for fertiliser reduction and efficiency enhancement at present.In this paper,a group of phosphorus-solubilizing bacteria were screened from the inter-root soil of rice,identified by molecular biology,and the phosphorus-solubilizing characteristics and phosphorussolubilizing mechanism of high-efficiency phosphorus-solubilizing bacteria were investigated,and the rice-promoting effect of high-efficiency phosphorus-solubilizing bacteria was studied.The following results were achieved:(1)Rice inter-root soil was isolated and purified from organic/inorganic phosphorus solubilizing solid media,and five inorganic phosphorus solubilizing bacteria and five organicinorganic dual phosphorus solubilizing bacteria were obtained from the screening.After 16 S r RNA sequencing analysis and phylogenetic tree construction,the inorganic phosphate solubilizing bacteria were identified as Priestia megaterium WSH-002,Lysinibacillus sp,Priestia megaterium strain,Massilia agri strain,Lysinibacillus sp and Lysinibacillus sp.Lysinibacillus sphaericus,belonging to the genera Marcella,Streptomyces and Bacillus,respectively.The organic-inorganic dual phosphate solubilizing bacteria were Bacillu aryabhattai,Bacillus altitudinis,Bacillus nealsonii,Bacillus megaterium,and Bacillus thuringiensis,all belonging to the genus Bacillus.(2)The bacteria were cultured in organic and inorganic phosphorus identification media,and the phosphorus content in the media was determined by molybdenum antimony anticolorimetric method at the end of the culture,and the phosphorus solubilizing ability of the phosphorus solubilizing bacteria was identified after comparison with the control media without the addition of bacteria.The results showed that all the phosphorus solubilizing bacteria had good phosphorus solubilizing ability,and the phosphorus solubilizing ability of Bacillus megaterium was the strongest among the double phosphorus solubilizing bacteria,and the effective phosphorus content in the identified medium increased by 2171.96% compared with the control.The best inorganic phosphate solubilizing bacteria was Bacillus sphericus,and the effective phosphorus content in the identification medium increased by 450.56%compared with the control.It was also found that the growth process of phosphorus solubilizing bacteria all led to a decrease in the pH of the medium,and the determination by high performance liquid chromatography revealed that phosphorus solubilizing bacteria mainly solubilized phosphorus by secreting organic acids such as oxalic acid,acetic acid,tartaric acid,malic acid,oxalic acid,citric acid and succinic acid.(3)Soils with two different phosphorus contents,low phosphorus and normal phosphorus,were selected and inoculated with screened phosphorus-dissolving bacteria,and incubated in an incubator for 7 days in pure soil,and then the effective phosphorus content of the soil and its related indexes were measured.The results showed that the inoculation of the phosphate solubilising bacteria significantly increased the effective phosphorus content,microbial phosphorus content and acid phosphatase(ACP)activity,alkaline phosphatase(ALP)activity and phytase activity of the soil,while significantly lowering the soil pH.This indicates that the phosphate solubilising bacteria increased the release of effective soil phosphorus by lowering soil pH and increasing soil acid phosphatase,alkaline phosphatase and phytase activities.(4)Two rice varieties,Nipponbare and kasalath,were selected as the experimental rice.The cultivated Bacillus megaterium and Bacillus thuringiensis were resuspended in two types of soil,low phosphorus and normal phosphorus,at a ratio of 12 m L bacterial resuspension/100 g soil,and two treatments were set up for potting trials with and without phosphorus fertilizer.Soil samples were collected at the tillering,tassel and maturity stages of rice and the relevant indexes were measured.It was found that the effective phosphorus content of the rice interrhizosphate soil inoculated with phosphorus-dissolving bacteria increased significantly,and the activities of soil acid phosphatase,alkaline phosphatase and phytase in the rice interrhizosphate soil were increased,which improved the net photosynthetic rate of rice and ultimately promoted the growth of rice.