Legacy effects of 8-year nitrogen inputs on bacterial assemblage in wheat rhizosphere

This study focused on the legacy effects of 8-year application of N (in gradient of 0, 140, 280, 470, and 660 kg N ha(-1) year(-1)) on the bacterial community diversity, interactions, and assembly processes in the wheat rhizosphere. The rhizosphere bacterial alpha-diversity increased with the rate of historical N input, while it did not change at N addition rates of over 280 kg N ha(-1) year(-1). Historical N input clearly shifted the rhizosphere bacterial community composition, and soils with more N input were more dissimilar to those without N input. The net relatedness index (NRI) and nearest taxon index (NTI) analysis revealed that the rhizosphere bacterial communities in most samples were phylogenetically clustered, and the treatments with high N (> 470 kg N ha(-1) year(-1)) showed higher levels of clustering than those with low N (< 140 kg N ha(-1) year(-1)), indicating more environmental selection stress in soil with higher historical N input. Increased co-occurrence network size and connectivity were accompanied by increased aboveground biomass of wheat. Overall, with the increase in historical N input, the resulting legacy effects forced the bacterial community in the rhizosphere to undergo higher environmental selection pressure, and indirectly affected the complexity of wheat rhizosphere assemblages during subsequent crop growth.