| To explore the effect of the combination use of PGPR(plant growth promoting rhizobacteria,PGPR)plus the reduction use of chemical fertilizer on the quality flue-cured tobacco cultivation soil,and to further optimize the fertilization regimes used in flue-cured tobacco cultivation,reducing the amount of chemical fertilizer,protect the production efficiency of flue-cured tobacco and the quality of tobacco-cultivation soil.Based on the tranditional tobacco cultivation site established in Gulin county,Luzhou city,Sichuan province,five fertilization treatments [i.e.T1: conventional fertilization,T2:conventional fertilization + PGPR,T3: PGPR + 10% RCF(reduction of 10% of the total amount of the chemical fertilizers used in conventional fertilization),T4: PGPR+20% RCF,T5: PGPR+30% RCF] were set up.And the effect of the different fertilizer treatments on the agronomic traits,yield and quality of flue-cured tobacco were evaluated.Moreover,the impacts of different fertilizer treatments on the soil physicochemical parameters,heavy metal contents,and the diverisity and composition of eubacterial community and the nos Z-type denitrifying bacterial community were also analyzed by chemical analysis,and molecular methods including denature gradient gel electrophoresis(DGGE)and cloning.The main results are list as following:(1)The combination use of PGPR inoculants plus conventional fertilization would significantly increase the agronomic traits,yield,output value,and chemical composition of the flue-cured tobacco plants(P<0.05).Among the five different fertilizer treatments,T2 treatment was the best one for flue-cured tobacco cultivation.In total,the application of PGPR inoculants had a positive effect on the growth,yield and quality of flue-cured tobacco.(2)With the combine use of PGPR inoculant plus conventional fertilization treatment,the content of soil available nitrogen was increased.The content of alkali-hydrolyzable nitrogen under T3 treatment was the highest.Total nitrogen,available potassium,and available phosphorus all exhibited the same variation trend as the alkaline dissolved nitrogen.The PGPR inoculant combined with the reduction of chemical fertilizer significantly increased soil p H and organic matter.The highest soil p H and organic matter content were detected in the T3 treatment.In addition,the combination use of PGPR inoculants and reduction of chemical fertilizers decreased the content of soil heavy metals including Cu,Pb and Cd.Totally,PGPR inoculation with the reduction of chemical fertilizer had significantly affect on the soil physicochemical properties and heavy metal contents.(3)The DGGE profiles revealed that some specific dominant bands were detected in the soil treated with different fertilizer treatments compared with the control.Soil bacterial community composition under T3 treatment was the most complex.In addition,the Shannon diversity index(H),richness(S),evenness(Eh),and dominance(C)of the bacterial communities were higher in the soils treates with PGPR inoculum than those in the CK soil.Phylogenetic analysis showed that members of genera Pseudomonas were the common and dominant species the experiment soil.Genus Acinetobacter and Bacillus were only detected in the soil under T2 and T3 treatments.Methylobacterium hispanicum was only found in the T5 soil.In general,PGPR inoculants combined with the redction use of chemical fertilizer changed the composition of the soil bacterial community compostion.(5)Canonical Correspondence Analysis(CCA)was used to analyze the correlations between the soil physicochemical,and the community composion of eubacteria.The results showed that soil available phosphorus(AP),available potassium(AK),water content(WC)and Pb,Cd,Cu were the key factor in shaping the soil bacterial community composition while soil total nitrogen(TN),p H and soil organic matter(SOM)were the second important edaphic parameters in affecting the bacterial community composition. |
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