适应玉米的溶磷细菌筛选及其对玉米生长的影响

从石灰性土壤中分离获得4株高效溶磷细菌X5、X6、Z4和Z8,研究其生物学特征,探索其单独及复合的溶磷促生潜能。研究发现菌株X5、X6、Z4和Z8均可以利用玉米根系分泌物作碳源生长。菌株X6和Z4均能产生吲哚乙酸(IAA)和铁载体,菌株Z8可产生IAA不产生铁载体,菌株X5可产生铁载体不产生IAA。盆栽试验结果表明,接种单一溶磷菌及4株菌复合处理均可促进玉米生长,但复合菌群的溶磷促生效果显著高于单一菌株。通过16S r RNA基因序列分析研究菌株的分类地位,初步鉴定X5、X6、Z4、Z8分别为荧光假单孢菌(Pseudomonas fluorescens)、草假单胞菌(Pseudomonas poae)、巨大芽孢杆菌(Bacillus megaterium)和枯草芽孢杆菌(Bacillus subtilis)。

Screening of Phosphate-solubilizing Bacteria Adaptable to Corn and Effects of the Bacteria on the Growth of Corn

Phosphate-solubilizing bacteria(PSB)are a group of beneficial bacteria capable of hydrolyzing organic and inorganic phosphorus from insoluble compounds. P-solubilization ability of the microorganisms is considered to be one of the most important traits associated with plant phosphate nutrition. A number of PSB strains have been screened out from soils in laboratory,however,few reports are available on their successful application in fields. More and more evidence suggests that root colonization of PSB is very important for phosphate solubilization;therefore,survivability of PSB in plant rhizosphere is one of the basic principles for PSB screening. In present study,20 strains of PSB with phosphate solubilization halos ranging from 7.9~20 mm were isolated from the rhizosphere of the corn growing in calcareous soil with the Pikovskaya medium plate method. Ten of the 20 strains of PSB,coded as X3,X5,X6,Z2,Z3,Z4,Z5,Z7,Z8 and Z9,with bigger phosphate solubilization halos were further tested for phosphate-solubilizing capacity in the NBRIP medium. Results show that gram-negative(G-)PSB(X3,X5,X6,Z2,Z3andZ5)solubilized much more phosphate than gram-positive(G+)ones(Z4,Z7,Z8 and Z9)did. The mean phosphate concentration in the NBRIP medium of the G- PSB treatments was 449.7 μg ml-1,with phosphate concentration in Treatment G- PSB Z3 being the highest,reaching to 562.2 μg ml-1. However,the highest phosphate concentration obtained by G+ PSB was only 46.9 μg ml-1. In further experiment,8 strains of PSB(G+:Z4, Z7,Z8 and Z9;and G-:X5,X6,Z3 and Z5)were evaluated for corn root exudate utilization capacity. All of the 8 strains of PSB were found to be able to utilize corn root exudate as sole carbon source and the G-PSB grew much better than G+ ones. Consistent with the findings in the culture in NBRIP medium,G- PSB solubilized much more phosphate than G+ PSB did when using corn root exudate as sole carbon source. Based on phosphate-solubilization and root exudate utilization capacities,two G- strains of PSB,X5(Pseudomonas fluorescens)and X6(Pseudomonas poae),and two G+ strains of PSB,Z4(Bacillus megaterium)and Z8(Bacillus subtilis)were selected for further experiment to test their IAA and siderophore production and phosphate solubilization capacities and effect on corn growth in greenhouse. X6 and Z4 was found to be able to produce both IAA and siderophore. Z8 was able to produce IAA but not siderophore,and X5 was able to produce siderophore but not IAA. The greenhouse experiment shows that application of mixture or any one of the four strains of PSB increased corn biomass and soil available phosphate,as compared with the control(no inoculation). Z4 was found to be the highest in effect on plant growth(plant height and dry weight)among the four tested strains of PSB. The treatments inoculated with mixture of PSB strains were significantly higher the treatments inoculated with only one single strain in soil available phosphate content and corn biomass Therefore,it can be concluded that X5(P. fluorescens),X6(P. poae),Z4(B. megaterium)and Z8 (B. subtilis)are potential PSB that can be prepared into a mixed inoculum or an efficient bio-fertilizer for use in areas deficient in P to improve overall performance of the crops therein.