Diversity and composition of active and total bacteria in rhizospheric soil in response to continuous cropping years of Panax notoginseng.

The synchronous research and analysis of total and active soil microbial communities can provide insight into how these communities are impacted by continuous cropping years and pathogen infection. The diversity of total and active bacteria in rhizospheric soil of 2-year-old and 3-year-old healthy and diseased Panax notoginseng can comprehensively reveal the bacterial response characteristics in continuous cropping practice. The results showed that 4916 operational taxonomic units (OTUs) were found in the rhizospheric soil bacterial community of P. notoginseng at the DNA level, but only 2773 OTUs were found at the RNA level. The rhizospheric environment had significant effects on the active and bacterial communities, as indicated by the number of OTUs, Shannon, Chao1, Faith's phylogenetic diversity (Faith's PD), and Simpson's diversity indexes. The DNA level can better show the difference in diversity level before and after infection with root rot. The bacterial Chao1 and Faith's PD diversity indexes of 2-year-old root rot-diseased P. notoginseng rhizospheric soil (D2) were higher than that of healthy plants, while the bacterial Shannon diversity index of 3-year-old root rot-diseased P. notoginseng rhizospheric soil (D3) was the lowest in the total bacteria. Principal coordinate analysis (PCoA) illustrated that the total bacterial species composition changed markedly after root rot disease. There were significant differences in the composition of active bacterial species between the 2-year and 3-year rhizospheres. In conclusion, the total and active edaphic rhizospheric bacterial communities could provide important opportunities to understand the responses of bacteria to continuous cropping of P. notoginseng.

Liu Y ，Bao L ，Sun W ，Cui Y ，Li X ，Ji X ，Wei Y ，Tan Y ... -  《-》

Rhizospheric soil and root endogenous fungal diversity and composition in response to continuous Panax notoginseng cropping practices.

Rhizosphere and endophytic fungal communities are considered critically important for plant health and soil fertility. In response to continuous cropping, Panax notoginseng becomes vulnerable to attack by fungal pathogens. In the present study, culture-independent Illumina MiSeq was used to investigate the rhizospheric and root endophytic fungi in response to continuous Panax notoginseng cropping practices. The results demonstrated that fungal diversity is increased inside the roots and in rhizospheric. Ascomycota, Zygomycota, Basidiomycota and Chytridiomycota were the dominant phyla detected during the continuous cropping of Panax notoginseng. The fungal diversity in the rhizospheric soil and roots of root-rot P. notoginseng plants are less than that of healthy plants in the same cultivating year, thus showing that root-rot disease also affects the community structure and diversity of rhizospheric and root endophytic fungi. Similarities in the major fungal components show that endophytic fungal communities are similar to rhizospheric soil fungal community based on a specialized subset of organisms. Canonical correspondence analysis on the fungal communities in root-rot rhizospheric from both healthy plants and rotation soils reveals that the soil pH and organic matter have the greatest impact upon the microbial community composition during continuous cropping, whereas soil nutrition status does not significantly affect the fungal community composition in response to continuous cropping practices. In addition, the results suggest that the unclassified genera Leotiomycetes, Cylindrocarpon, Fusarium and Mycocentrospora are shown as the potential pathogens which are responsible for the obstacles in continuous cropping of P. notoginseng. Further exploration of these potential pathogens might be useful for the biological control of continuous cropping of P. notoginseng.

Tan Y ，Cui Y ，Li H ，Kuang A ，Li X ，Wei Y ，Ji X ... -  《-》

Diversity and composition of rhizospheric soil and root endogenous bacteria in Panax notoginseng during continuous cropping practices.

Rhizobacteria and endophytic bacteria play important roles in protecting host plants from infection by phytopathogens, which cause soil-borne diseases and severely impair plant health. Panax notoginseng is negatively affected by continuous cropping and becomes vulnerable to attack by microbial pathogens. In the present study, culture-independent Illumina MiSeq was used to investigate root-endophytic and rhizospheric bacteria in response to continuous cropping of P. notoginseng. Numbers of rhizospheric bacteria decreased with continuous P. notoginseng cropping, while the effects of continuous cropping on endophytic bacteria were not statistically significant. Bacterial diversity was higher in healthy P. notoginseng rhizospheric soils and roots than in those of diseased P. notoginseng. The most dominant phyla detected during continuous cropping were Proteobacteria, Cyanobacteria, Actinobacteria, and Acidobacteria. The genera Pseudomonas, Rhodoplanes, Candidatus Solibacter, and Streptomyces were dominant in P. notoginseng rhizospheric soils and roots. Erwinia, Stenotrophomonas, Pseudomonas, and Sphingobium were specifically detected in relatively high proportions among root-rot rhizospheric bacteria and endogenous root bacteria in plants under continuous cropping, suggesting that they may be the pathogens responsible for the negative effects of continuous cropping on P. notoginseng. Based on canonical correspondence analysis of the bacterial communities that were identified from healthy plants and fallow soils, total phosphorus (P), pH, and organic soil matter exerted the greatest impacts upon bacterial community composition during continuous cropping. In general, continuous cropping practices for P. notoginseng and severe root-rot disease notably affected the community structure and the diversity of rhizospheric and root endophytic bacteria. Our study elucidated the ecological significance of microbial communities in healthy plant maintenance, and our results may inform biological control strategies during the continuous cropping of P. notoginseng.

Tan Y ，Cui Y ，Li H ，Kuang A ，Li X ，Wei Y ，Ji X ... -  《-》

[Microbial distribution and 16S rRNA diversity in the rhizosphere soil of Panax notoginseng].

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Molecular characterization of microbial communities in the rhizosphere soils and roots of diseased and healthy Panax notoginseng.

Wu Z ，Hao Z ，Zeng Y ，Guo L ，Huang L ，Chen B ... -  《-》