| Sugarcane is not only the most important sugar crop,but also the most important economic crop in Guangxi,China.In sugarcane production,the application of large amount of chemical fertilizer seriously restricts the sustainable development of sugarcane industry.Nitrogen fixing bacteria can promote the cycling and transformation of soil nutrients.A large number of studies had confirmed that endophytic nitrogen fixing bacteria could colonize in plant roots and body,and secrete organic acids to activate soil nutrients,improve soil rhizosphere microbial community,promote plant absorption and utilization of mineral nutrients,and then promoted the plant growth.It is of great significance to study the effect of endophytic nitrogen fixing bacteria on soil nutrient activation and sugarcane growth promotion for improving soil quality and sugarcane yield.In this study,four strains of nitrogen fixing bacteria DX120E(Klebsiella variicola),CA1(Bacillus mycoides),WZS021(Streptomyces chartreusi)and CN11(Pseudomonas mosselii)were used to treat soil,and the effects of each single strain and strain combination treatments on three main nutrients and organic acid contents were analyzed.Meanwhile,the effects of the treatment strain on promoting the growth of sugarcane were discussed in pot experiment by researching the agronomic characters,physiological characteristics,soil nutrition and enzyme activity,and the metabonomics analysis of stem and leaves in sugarcane variety B8 and ROC22 inoculated with DX120 E strain were also studied.The main results are as follows:1.The contents of nitrate nitrogen,ammonium nitrogen,hydrolytic nitrogen,available phosphorus,available potassium,slowly available potassium and organic acid were increased,while the content of inorganic phosphorus was decreased,and the difference was significant compared with the blank control.Three better treatments were got by the membership function method,which were DX120 E,CN11+DX120E and CA1+DX120E+WZS021 respectively.2.The results showed that the plant height,chlorophyll content,brix and aboveground and underground biomass of two sugarcane varieties B8 and ROC22 were improved after treatment,but the differences were different in different treatments.DX120 E and PAL5 had the best biomass in the two sugarcane varieties.The biomass of sugarcane varieties B8 and ROC22 increased by 2.16 times and 0.60 times respectively compared with the control,and DX120 E increased by 1.86 times and 0.39 times respectively.The activity of nitrate reductase(NR)in leaves of sugarcane varieties B8 was the highest in PAL5 treatment,which was 40.82% higher than that of CK;In ROC22,the NR activity of DX120 E treatment was significantly higher than that of the control,which was 1.12 times higher than that of the control.The activities of glutamine synthetase(GS),sucrose synthetase and sucrose phosphate synthetase(SS,SPS)of the two sugarcane varieties were the highest at 60 days after treatment.3.The inoculated treatment effected the soil nutrients and enzymes.The results showed that the contents of nitrate nitrogen,ammonia nitrogen,hydrolytic nitrogen,available phosphorus,available potassium,slowly available potassium,the activities of soil enzymes increased significantly,and the content of inorganic phosphorus decreased in the pot experiment at different treatment stages,with significant differences compared with the blank control,but the differences were different among different treatments.The content of nitrate nitrogen in the soil of sugarcane variety B8 increased with the sugarcane growth,but increased first and then decreased in sugarcane variety ROC22.The inoculation of bacterial strains increased the content of ammonia nitrogen in the soil of the two varieties,decreased the content of hydrolytic nitrogen,available phosphorus and inorganic phosphorus.The effects on activation of N,P and K in CA1+DX120E+WZS021 treatment was significantly lower than that in the other two treatments.4.Metabonomics of sugarcane stems and leaves inoculated with DX120 E were analyzed by LC-MS.The results showed that the type and contents of the metabolites of sugarcane leaves after DX120 E treatment were higher than those of stems.The main metabolites were amino acids,nitrogenous compounds,organic acids,carbohydrates and carbohydrates.After inoculation with DX120 E,the differential metabolites in stems and leaves of sugarcane variety B8 were generally down-regulated,while up-regulated in stems and down-regulated in leaves of sugarcane variety ROC22.Cluster heat map analysis showed that there were significant differences in the contents of 62 metabolites in stems and 115 metabolites in leaves of sugarcane variety B8,and 53 metabolites in the stem and 101 metabolites in the leaves of ROC22.The results of KEGG showed that metabolic pathways were mainly related to the amino acid pathways.The DX120 E inoculated treatment were benefit to the nitrogen and carbon metabolism of sugarcane by affecting glycolysis and TCA cycle.In conclusion,the inoculation strains could improve the rhizosphere soil environment of sugarcane.DX120 E could affect the nitrogen and carbon metabolism pathway of sugarcane and promote the growth of sugarcane.The results of this study can provide a theoretical basis for the application of different endophytic nitrogen fixing bacteria in sugarcane cultivation,such as fertilizer reduction,and the useful reference for understanding the growth promoting mechanism interaction with sugarcane. |
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