Soil bacteria are very important in biogeochemical cycles and play significant role in soil-borne disease suppression. Although continuous cropping is responsible for soil-borne disease enrichment, its effect on tobacco plant health and how soil bacterial communities change are yet to be elucidated. In this study, soil bacterial communities across tobacco continuous cropping time-series fields were investigated through high-throughput sequencing of 16S ribosomal RNA genes. The results showed that long-term continuous cropping could significantly alter soil microbial communities. Bacterial diversity indices and evenness indices decreased over the monoculture span and obvious variations for community structures across the three time-scale tobacco fields were detected. Compared with the first year, the abundances of Arthrobacter and Lysobacter showed a significant decrease. Besides, the abundance of the pathogen Ralstonia spp. accumulated over the monoculture span and was significantly correlated with tobacco bacterial wilt disease rate. Moreover, Pearson's correlation demonstrated that the abundance of Arthrobacter and Lysobacter, which are considered to be beneficial bacteria had significant negative correlation with tobacco bacterial wilt disease. Therefore, after long-term continuous cropping, tobacco bacterial wilt disease could be ascribed to the alteration of the composition as well as the structure of the soil microbial community.
BackgroundThe interaction mechanism between crop and soil microbial communities is a key issue in both agriculture and soil ecology. However, how soil microbial communities respond to crop planting and ultimately affect crop health still remain unclear. In this research, we explored how soil microbial communities shifted during tobacco cultivation under different rotation systems (control, maize rotation, lily rotation and turnip rotation).ResultsOur analyses showed that soil microbial communities had a general response pattern to tobacco planting, as the abundances of Proteobacteria and Planctomycetes increased while Acidobacteria and Verrucomicrobia decreased during tobacco cultivation, no matter which rotation system was adopted. Notably, tobacco decreased the diversity and co-occurrence of soil microorganisms, but maize rotation might suppress tobacco bacterial wilt by alleviating the decrease in biodiversity and co-occurrence. Molecular ecological network analysis indicated that there was stronger competition between potential disease suppressive (e.g., Acidobacteria) and inducible bacteria (e.g., Chloroflexi) in maize rotation systems. Both soil properties (e.g., pH, Ca content) and microbial communities of tobacco mature period depended on their counterparts of fallow period, and all these factors shaped tobacco disease comprehensively.ConclusionsBoth soil microbial communities of fallow stage and tobacco selection shaped the communities of tobacco mature stage. And effective rotation crop (maize) could decrease the incidence of tobacco bacterial wilt by alleviating the decrease in diversity and co-occurrences of microbial populations. This study would deepen our understanding about succession mechanism of soil microbial communities during crop cultivation and their relationship with crop health.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-016-0845-x) contains supplementary material, which is available to authorized users.
Rotation is an effective strategy to control crop disease and improve plant health. However, the effects of crop rotation on soil bacterial community composition and structure, and crop health remain unclear. In this study, using 16S rRNA gene sequencing, we explored the soil bacterial communities under four different cropping systems, continuous tobacco cropping (control group), tobacco-maize rotation, tobacco-lily rotation, and tobacco-turnip rotation. Results of detrended correspondence analysis and dissimilarity tests showed that soil bacterial community composition and structure changed significantly among the four groups, such that Acidobacteria and Actinobacteria were more abundant in the maize rotation group (16.6 and 11.5%, respectively) than in the control (8.5 and 7.1%, respectively). Compared with the control group (57.78%), maize and lily were effective rotation crops in controlling tobacco bacterial wilt (about 23.54 and 48.67%). On the other hand, tobacco bacterial wilt rate was increased in the turnip rotation (59.62%) relative to the control. Further study revealed that the abundances of several bacterial populations were directly correlated with tobacco bacterial wilt. For example, Acidobacteria and Actinobacteria were significantly negatively correlated to the tobacco bacterial wilt rate, so they may be probiotic bacteria. Canonical correspondence analysis showed that soil pH and calcium content were key factors in determining soil bacterial communities. In conclusion, our study revealed the composition and structure of bacterial communities under four different cropping systems and may unveil molecular mechanisms for the interactions between soil microorganisms and crop health.
The effects of high potassium and normal potassium treatments on protein expression in roots of flue-cured tobacco plant HKDN-5 at the seedling stage were analyzed by an unlabeled protein quantification technique. The results showed that 555 proteins were differentially expressed (245 proteins were down-regulated and 310 proteins were up-regulated) in high potassium treatment compared with normal potassium treatment. Differentially expressed proteins were involved in 96 metabolic pathways (42 metabolic pathways, 21 synthetic pathways as well as catabolic pathways, including fatty acid metabolism, phenylpropane biosynthesis, ketone body synthesis and degradation, and butyric acid metabolism. Root processing of high potassium concentrations leads to increases in the synthesis of peroxidase, superoxide dismutase and acyl-coenzyme-A synthetase. Additional proteomic differences observed in tobacco roots grown in high potassium include proteins involved with genetic information processing as well as environmental sensing. Examples include RNA helicase, ABC transporters and large subunit GTPases. These up-regulated differentially expressed proteins function mainly in protein translation, ribosome structure and protein synthesis. This indicates that under high potassium treatment, root protein synthetic processes are accelerated and substance metabolism pathways are enhanced; thus, providing the material and energetic basis for root growth.
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