Long Term Monocropping Effects Tobacco Yield by Regulating Rhizosphere Allelochemicals and Microbial Community

Long term monocropping is considered to change soil chemical properties and affect the yield. It is significant to study the relationship among soil character, rhizosphere microorganism and crop yield under long term monocropping, to clarify the mechanism of monocropping obstacle. In this work, a continuous cropping area of tobacco in Southwest China was selected, in which Nicotiana tabacum cv. Yunyan87 was planted. The disease incidence, yield, soil properties, rhizosphere allelochemicals and microbial community were determined in the mature phase of tobacco with treatments for 2 (MCC2), 3 (MCC3), 4 (MCC4), 5 (MCC5), and 15 years (MCC15) of continuous cropping. In the results, the continuous cropping barrier was serious in the first 5 years, however, after 15-year continuous cropping, the yield was gradually recovered, and the soil-borne diseases were significantly inhibited. In terms of allelochemicals, the concentration of myristic acid increased with the time of monocropping, except for MCC15. Additionally, 2,2′-methylene bis-(4-methyl-6-tert-butylphenol) and dioctyl phthalate were lower in MCC15 than other treatments. After different monocropping years, the structure of bacterial community was distinct, with no significant differences in diversity index. For bacteria, the dominant phyla in all the treatments were Proteobacteria , followed by Acidobacteria , and Actinobacteria . In addition, in MCC15, showed relative abundances in beneficial bacterial genera like Sphingomonas and Gemmatimonas , that are involved in disease suppression and plant growth, were increased. For fungi, the dominant phyla in all the treatments were Ascomycota , followed by Mortierellomycota . Moreover, compared with MCC5 treatment, the relative abundance of pathotroph in MCC15 treatment decreased by 31.52%, the relative abundance of saprotroph increased by 31.90%. The relative abundance of potential pathogen fusarium in rhizosphere soil was the highest at the mature stage of tobacco crop rotation (MCR). Hence, different from the short-term monocropping, the 15-year long-term tobacco monocropping showed a gradual restoration of microbial community structure and specific genera, while reducing the accumulation of specific allelochemicals, thus relatively recovering the yield. It is expected to provide a reference for further understanding the mechanism of continuous cropping obstacle.