Direct and indirect linkages between soil aggregates and soil bacterial communities under tillage methods

Abstract

Tillage methods affect soil aggregates and influence soil bacterial communities. However, the direct and indirect linkages between soil aggregates and soil bacterial communities are still not clear. In this study, we studied the linkages between soil bacterial diversity and soil aggregates under three tillage types (conventional tillage, CT; no tillage, NT; and subsoiling tillage, ST). All of the tillage methods were conducted for 10 years. After 10 years, soil aggregates and bacterial communities differed significantly among the three tillage types. Compared to the CT treatment, the NT treatment significantly increased the >1 mm soil aggregates (P < 0.001), and the ST treatment significantly increased the 0.25–1 mm soil aggregates (P < 0.029), while compared to the NT and ST treatments, the CT treatment increased the <0.25 mm soil aggregates (P < 0.001). Tillage affected the soil bacterial alpha diversity such that the order of the ACE index and the Shannon index was NT > CT > ST, and it influenced four bacterial communities (Chloroflexi, gamma-Proteobacteria, delta-Proteobacteria and Verrucomicrobia). Spearman correlation analysis suggested the >1 mm soil aggregates showed a positive correlation with the soil bacterial alpha diversity (species, Shannon and ACE indices), but the correlation with the <1 mm soil aggregates was negative. An SEM analysis showed that the soil aggregates explained 68.4% of the variation in the soil bacterial community, with direct linkage accounting for 38.97% and indirect linkage accounting for 29.43%. Furthermore, the indirect linkage was mainly due to changes in the soil organic matter (SOM: 11.17%), available phosphorus (AP: 8.06%), and soil water content (water: 10.20%). Overall, our results showed two procedures of soil aggregation and soil bacterial communities, suggesting the direct and indirect linkages between soil aggregates and soil bacterial communities, and our results will help us to better understand the relationship between soil aggregates and bacterial communities and to manage soil bacteria that may be useful in improving soil productivity.