PacBio Sequencing Unravels Soil Bacterial Assembly Processes along a Gradient of Organic Fertilizer Application.

The application of organic fertilizer is an important agricultural practice for improving soil health and the soil microflora, and the microbial community assembly process relating to this application is also closely associated with soil health. However, the effects of organic fertilizer intensification on the bacterial community assembly processes of farmland soil are often overlooked. In this study, bacterial community structure, ecological networks, and bacterial community assembly processes were evaluated using the investment soil-cultivation test and PacBio sequencing. The PCoA, Mantel test, and Procrustes analysis showed that overfertilization changed soil physicochemical properties and caused significant succession of soil bacterial communities (p < 0.05). The neutral community model indicated that the spread of bacteria in the low-fertilization group was greater than that in the high-fertilization group. Under conditions of overfertilization via organic fertilizer (organic matter ≥ 50% and N-P2O5-K2O ≥ 5%), the bacterial network topology and stability of nutrient-rich loess brown (H) soil were improved compared with those of red (R) soils, and the slope of the robustness analysis displayed a 10.9% decrease in H soil and a 37.2% decrease in R soil. The inference of community assembly mechanisms via phylogenetic-bin-based null model analysis (iCAMP) confirmed that with increasing fertilization, the relative importance of ecological drift gradually increased, and the importance of homogeneous selection was reduced (p < 0.01, permutational ANOVA). A total of 103 bins (in the selected top 200 bins) of the dominant process were different between the H and R soils. The results clarified that homogeneous selection and drift were the dominant processes driving the assembly of bacterial communities in different soil types along the gradient of organic fertilizer application and confirmed that excessive fertilization enhanced the relative importance of drift among the construction mechanisms. Changes in soil construction mechanisms due to overfertilization are related not only to soil type but also to different microbial lineages. [ABSTRACT FROM AUTHOR]