Hongli Li

In this study, to evaluate the effect of different biocontrol agents (BCAs) on the soil bacterial community, we investigated the effects of Bacillus amyloliquefaciens, synthetic bacterial community (Aspergillus niger:Bacillus subtilis:Bacillus licheniformis:Streptomyces microflavus = 3:3:3:1, SynCom), and BCAs combined with lime-nitrogen on soil bacterial community by utilizing 16S rRNA sequencing technology. The sequencing shows that BCAs application can improve the value of Shannon and Sobs index of bacterial community during tobacco rosette and vigorous growing period. With the growth of tobacco, the effect of BCAs on the composition and difference of soil bacterial community structure becomes more and more obvious. In terms of average relative richness, the top six phyla of soil bacterial community are Proteobacteria, Actinobacteria, Chloroflexi, Acidobacteria, Gemmatimonadetes, and Bacteroidetes. Bacillus amyloliquefaciens application can increase the relative richness of Proteobacteria and Bacteroidetes. And the combination between BCAs and lime-nitrogen can increase the relative richness of Gemmatimonadetes and Bacteroidetes. The SynCom also can increase the relative richness of Bacteroidetes, whereas it decreases the relative richness of Acidobacteria. Proteobacteria, Acidobacteria, Gemmatimonadetes, and Bacteroidetes showing an extremely significant correlation with pH and exchangeable magnesium (EMg). BCAs application can improve the tobacco yield, effective leaves, and reducing sugar content that also has extremely significant positive correlation with pH and EMg. In conclusion, the results of our field experiments clearly show that BCAs application can significantly affect the soil pH and EMg by changing most of the dominant soil bacterial species. The richness of Bacteroidetes can serve as an indicator of the changes in soil pH and EMg caused by BCAs application.

The dry anaerobic digestion performances were investigated at the temperature of 35±1°Cwith addition of propionic acid at different concentrations in five lab-scale reactors (R1-R5) to investigate the effect of propionic acid accumulation on methane production in dry mesophilic anaerobic digestion. And the volatile fatty acids, biogas and microbial community were detected. The active of microbial community and the methane generation would be inhibited when the propionic acid exceeded 30 gL¹, which affected not only syntrophic propionate-oxidizing bacteria but also acetate-utilizing methanogens. Eubacteria decreased sharply accompany with the higher concentration of propionic in R4 and R5. The relative abundance of acetoclastic methanogens was directly correlated with volatile solids removals and methane generation in dry anaerobic reactors. Otherwise, the quantity of syntrophic propionate-oxidizing bacteria was positively linear correlated with propionic acid when the concentration was below 30 gL¹. The methanogenic bacteria activity in R3 was the best with the methane yield of 27.01 mLCH₄ g^-1 VS d^-1. The results suggested that appropriate propionate could enhance methane production in the dry anaerobic fermentation.

Soil microorganism has a profound influence on planting growth and disease suppression. However, the difference in microbial community structure between suppressive and root rot-conducive soil and the mechanism of controlling soil-borne diseases by microorganisms in suppressive soil were not clear. To provide a theoretical foundation for prevention and control of root rot, this paper investigated the change of community structure in rhizosphere soil between suppressive and root rot-conducive tobacco fields. Soil samples were collected during before transplanting, vigorous growing period, and mature period of the tobacco, and bacteria and fungi were analyzed using 16S rRNA and 18S rRNA gene sequencing, respectively. Results showed that bacteria were more sensitive to the change between suppressive and root rot-conducive soil, and fungi were more sensitive to the change of different tobacco growth periods. Compared with conducive soil, tobacco suppressive soil can resist the invasion of pathogens, especially fungi, by regulating soil microbial community structure, and the potential pathogen Boeremia was always lower. Fusarium, the root rot pathogen, decreased rapidly in the mature period in suppressive soil. Moreover, norank_o_Gaiellales and unclassified_f_Trichocomaceae had a critical role in suppressive soil in the process of inhibiting root rot, which was obvious in the mature stage. Overall, the results indicated that the composition and structure of the microbial community significantly altered between suppressive and conducive soil along with the growth of tobacco, and suppressive soil could inhibit the occurrence of soil-borne diseases by boosting beneficial bacteria and inhibiting the potential pathogens.

In this article, the interaction between acetic acid and methanogenic bacteria activity was investigated. The dry anaerobic digestion was conducted with four lab-scale reactors (R1–R4) and acetic acid at different concentrations were fed as additional substrate to R1–R4. The results showed that the population of acetocastic-utilizing methanogens decreased along with the increasing of acetic acid, in which the concentration was above 120,000 mg·L^–1 during the stable stage with coefficient of 0.8984. The activity of methanogenic microorganisms in R2 was the best of all reactors. The maximal biogas production rate in R2 was 1.73 m³ m^–3 day^–1 with the methane content of 55%.