Variations in different preceding crops on the soil environment, bacterial community richness and diversity of tobacco-planting soil

Abstract

Tobacco (Nicotiana tabacum L.) is a major cash crop, and soil quality played a significant role in the yield and quality of tobacco. Most farmers cultivate tobacco in rotation with other crops to improve the soil characteristics. However, the effects of different previous crops on the soil's nutrient status and bacterial community for tobacco cultivation still need to be determined. Three treatments were assessed in this study, i.e., tobacco-planting soil without treatment (CK), soil with barley previously cultivated (T₁), and soil with rapeseed previously cultivated (T₂). The soil physical and chemical properties and the 16S rRNA gene sequence diversity of the bacterial community were analyzed. The effects of different crops on the physical and chemical properties of tobacco-planting soil and the diversity and richness of the bacterial community were comprehensively discussed. The results of this study showed that different previously cultivated crops altered the nutrient status of the soil, with changes in the ratio of NH₄ ⁺-N to NO₃ ^--N having the most significant impact on tobacco. In CK, the ratio of NH₄ ⁺-N to NO₃ ^--N was 1:24.2, T₁-1:9.59, and T₂-1:11.10. The composition of the bacterial community in tobacco-planting soil varied significantly depending on the previously cultivated crops. The richness and diversity of the bacterial community with different crops were considerably higher than without prior cultivation of different crops. The dominant bacteria in different treatments were Actinobacteriota, Proteobacteria, and Chloroflexi with their relative abundance differed. In conclusion, our study revealed significant differences in nutrient status, bacterial community diversity, and the richness of tobacco-planting soil after the preceding cultivation of different crops. Suitable crops should be selected to be previously cultivated in tobacco crop rotations in near future for sustainable agriculture.

Keywords: bacterial community; bacterial diversity; nutrient status; preceding crops; tobacco-planting soil.

Figure 1

Physical and chemical properties of tobacco-planting soil previously cultivated with different crops. (A) soil pH; (B) soil SOM; (C) soil total nitrogen; (D) soil total phosphorus; (E) soil total potassium; (F) soil NH₄⁺-N; (G) soil NO₃⁻-N; (H) soil available phosphorus; (I) soil available potassium. Different letters indicate significant differences between treatments (p < 0.05).

Figure 2

The analysis of bacterial α diversity in tobacco-planting soil with different previously cultivated crops. Different letters indicate significant differences between treatments (p < 0.05). (A) the bar graph of Chao1 index; (B) the bar graph of coverage index; (C) the bar graph of Shannon index; (D) the box graph of Chao1 index; (E) the bar graph of coverage index; (F) the bar graph of Shannon index; (G) the dilution curve of Chao1 index; (H) the dilution curve of coverage index; (I) the dilution curve of Shannon index.

Figure 3

Analysis of bacterial β diversity in tobacco-planting soil with different cultivated crops. (A) the PCA of bacterial communities among the different treatments; (B) the PCoA of bacterial communities among the different treatments; (C) the PCA box graph of bacterial communities among the different treatments; (D) the PCoA box graph of bacterial communities among the different treatments.

Figure 4

Venn diagram of bacterial species composition in tobacco-planting soil cultivated with different preceding crops. (A) the Venn of bacterial communities among CK, T1 and T2; (B) the Venn of bacterial communities among CK and T1; (C) the Venn of bacterial communities among CK and T2; (D) the Venn of bacterial communities among T1 and T2.

Figure 5

Composition of rhizosphere bacterial community in tobacco-planting soil cultivated with different preceding crops. (A) the community of barplot analysis; (B) the community analysis pieplot of CK bacterial communities on genus level; (C) the community analysis pieplot of T1 bacterial communities on genus level; (D) the community analysis pieplot of T2 bacterial communities on genus level.

Figure 6

Relationship between rhizosphere bacterial community composition of the different preceding crops and tobacco-planting soil properties. (A) the heatmap of soil bacterial communities among different treatments; (B) the ternary analysis of CK, T1 and T2 on family level; (C) the circos analysis of CK, T1 and T2 on phylum level.

Figure 7

Difference analysis of bacterial species in tobacco-planting soil cultivated with different preceding crops. (A) the Kruskal-Wallis H test bar plot of CK, T1 and T2 on class level; (B) the Kruskal-Wallis H test bar plot of CK, T1 and T2 on phylum level.

Figure 8

Species difference analysis of dominant bacterial species in tobacco-planting soil cultivated with different preceding crops. (A) the LEfSe multilevel species level tree from phylum to genus; (B) the LEfSE bar of LDA discriminant histogram.

Figure 9

Correlation analysis between the different preceding crops and the tobacco-planting soil environment characteristics.

Figure 10

Correlation analysis between the tobacco soil environment characteristics and the dominant bacterial species. (A) the two-factor correlation network diagram between species and environmental factors; (B) the heatmap of correlations between species and environmental factors.