Vertical differences in carbon metabolic diversity and dominant flora of soil bacterial communities in farmlands.

The carbon cycle in soil is significantly influenced by soil microbes. To investigate the vertical distribution of the dominant groups in agricultural soil and the carbon metabolic diversity of soil bacteria, 45 soil samples from the 0 ~ 50 cm soil layer in Hunan tobacco-rice multiple cropping farmland were collected in November 2017, and the carbon diversity of the soil bacterial community, bacterial community composition and soil physical and chemical properties were determined. The results showed that the carbon metabolic capabilities and functional diversity of the soil bacterial community decreased with depth. The three most widely used carbon sources for soil bacteria were carbohydrates, amino acids, and polymers. The dominant bacterial groups in surface soil (such as Chloroflexi, Acidobacteriota, and Bacteroidota) were significantly positively correlated with the carbon metabolism intensity. The alkali-hydrolysable nitrogen content, soil bulk density and carbon-nitrogen ratio were the key soil factors driving the differences in carbon metabolism of the soil bacterial communities in the different soil layers.

Deep tillage reduces the dependence of tobacco (Nicotiana tabacum L.) on arbuscular mycorrhizal fungi and promotes the growth of tobacco in dryland farming.

The traditional shallow tillage method reduces soil quality and affects the efficiency of agricultural production. Using conventional rotary tillage (12 cm) as the control, Yunyan 87 as the test variety, and paddy soil as the test site, we studied the effects of deep tillage (subsoiling 30 cm) on soil nutrients, arbuscular mycorrhizal fungi (AMF), and tobacco (Nicotiana tabacum L.) growth. The results showed that deep tillage increased the content of organic carbon, available phosphorus (AP), and available potassium (AK) in the 20-40 cm soil layer. The AMF community was also affected by deep tillage. Glomus, the dominant genus in both groups, increased significantly in soil after deep tillage. The AMF colonization rate was lower than that of conventional rotary tillage. Deep tillage was beneficial for tobacco growth in the middle and late stages. The root growth and nutrient content of the tobacco plants increased. Deep tillage significantly improved the output value of tobacco plants. Deep tillage is conducive to improving soil fertility, promoting the vigorous growth of roots, reducing the dependence of tobacco on AMF, and promoting the high quality and yield of tobacco in the drylands of Hunan.

Pseudomonas species isolated from tobacco seed promote root growth and reduce lead contents in Nicotiana tobacum K326.

Endophytic bacteria are generally helpful for plant growth and protection. We isolated from tobacco seeds three Pseudomonas strains (K03, Y04, and N05) that could produce siderophores, indole-3-acetic acid, and 1-aminocyclopropane-1-carboxylate deaminase, fix nitrogen, dissolve phosphorus and potassium, and tolerate heavy metals. In pot experiments, the three isolated strains significantly promoted root growth and increased the root enzyme activity in Nicotiana tobacum K326. Furthermore, bacterial inoculations increased the proportion of residual lead (Pb) by 8.36%-51.63% and decreased the total Pb content by 3.28%-6.38% in the contaminated soil during tobacco planting, compared with uninoculated soils. An effective decrease in Pb content was also found in tobacco leaves with bacterial inoculations. K03 inoculation decreased the Pb content in the upper leaves by 49.80%, and Y04 inoculation had the best effect, decreasing the Pb content in the middle leaves by 70.12%. Additionally, soil pH and root activity had significant effects on transformation and translocation of Pb. The study suggested that in response to Pb pollution in soil, a reasonable application of endophytes (e.g., Pseudomonas) might be a promising approach in promoting tobacco growth and reducing Pb content in tobacco, while simultaneously enhancing Pb stabilization in soils.