| Phosphorus(P)is one of the main macronutrients necessary for plant growth,while it is so easily mineralized in the soil that it is hard for plants to use.On the one hand,the available P in soil is insufficient and plant growth is restricted;on the other hand,the low-utilization efficiency of P fertilizer intensifies the abuse of P fertilizer.This not only increases planting costs and wastes resources,but also causes soil hardening and acidification,aggravation of diseases and insect pests,deterioration of agricultural products and eutrophication of water bodies.How to improve the utilization efficiency is the key to reduce the amount of P fertilizer and solve the problem of agricultural non-point source pollution.Phosphorus solubilizing bacteria(PSB)can transform the stable P into bioavailable P,supplement the essential nutrients for plant growth and improve the availability of P fertilizer.However,PSB has some problems in agricultural application,such as low survival rate,short validity period,easy degradation of bacteria species and poor P-solubilizing effect.Selenium nanoparticles(SeNPs)has environmental friendliness and superior biological characteristics,which can effectively promote plant growth,improve the biological activity of rhizosphere microorganisms,and increase the content of probiotics in soil.Meanwhile,SeNPs can exist stably in soil and be effective for a long time.At present,there are few studies on the effects of SeNPs on the physiology of PSB,and the molecular mechanism of its influence on PSB is still unclear.Based on this,this study combined SeNPs and PSB to form a new type of microbial fertilizer,to clarify the synergistic mechanism of SeNPs and PSB,and reveal the strengthening mechanism of SeNPs on PSB.It providing theoretical guidance and technical support for the practical application of SeNPs and PSB compound agent.The main contents and results of this paper are as follow:(1)A number of phosphorus-solubilizing bacteria were screened from the natural environment,and their phosphorus-solubilizing mechanism was elucidated,and the effects of phosphorus-solubilizing bacteria on tomato plant growth,rhizosphere soil and non-rhizosphere soil microbial community were revealed by molecular biology techniques.In this study,a total of seventeen strains PSB were screened from soil,which belonged to five genera including Bacillus,Palladium,oligomonas and Citrate bacteria.It was found that the PSB OP-1 releases insoluble calcium phosphate mainly by secreting small organic acids(mainly malic acid,with a small amount of acetic acid,succinic acid,lactic acid,citric acid,propionic acid and so on)and reducing the pH of the medium.Results of field experiments showed that single addition of exogenous PSB did not form dominant bacteria in soil,but the combination of PSB and compost caused changes in soil physical and chemical properties,and further changed the bacterial community structure in situ.(2)Nano-selenium was synthesized by bioreduction method.The effects of nanoselenium and selenite on the metabolic activities of bacillus and Escherichia coli,two typical soil microorganisms,were systematically studied,and the transformation process of exogenous nano-selenium and selenite in soil and its influence mechanism on soil microbial community were revealed.It was found that the biosynthesized SeNPs was an amorphous nanoform selenium with particle size between 187-279nm.It was attached to the surface and interior of microorganisms after biosynthesis,and its outer layer was wrapped with an extracellular polymer composed of proteoglycan.SeNPs was more stable in soil,while selenite was gradually converted to a more stable and less toxic state in soil.SeNPs promoted the propagation of soil probiotics,while selenite reduced the abundance and diversity of soil microorganisms,which may be related to the toxicity of persistent free radicals released during selenite transformation.Experiments on two typical soil microorganisms(E.coli and Bacillus)showed that SeNPs had low toxicity and high safety due to its slow entry into microorganisms.These results indicated that SeNPs is a kind of environment-friendly agricultural selenium additive.(3)Through the analysis of soil physical and chemical properties and plant growth,the synergistic mechanism of nano-selenium and phosphorus-solubilizing bacteria was clarified,and the strengthening mechanism of nano-selenium on phosphorussolubilizing bacteria was revealed through the analysis of the growth and phosphorussolubilizing ability of phosphorus-solubilizing bacteria.The results showed that SeNPs could regulate the phosphorus-solubilizing ability of PSB by changing the types and quantities of small organic acids secreted by PSB.In pot experiment.SeNPs could promote the phosphorus solubilizing effect of PSB in soil,and the types and quantities of small organic acids secreted in soil are different from those in medium.The application of PSB can improve the availability of phosphorus in soil and promote the growth of Brassica chinensis,especially the combination of SeNPs and PSB. |
PDF Full Text Request