Bacterial community composition is shaped by soil secondary salinization and acidification brought on by high nitrogen fertilization rates

Abstract High rates of nitrogen (N) fertilization have resulted in soil secondary salinization and acidification, particularly in intensively managed agricultural ecosystems. However, little is known about the long-term effects of high N fertilization rates on soil bacterial community composition and diversity. Barcoded pyrosequencing was used to investigate the bacterial community composition and diversity of soils in a greenhouse-based intensive vegetable agriculture system, in eastern China. The soils were subject to five N (urea) application rates that were 100%, 80%, 60%, 40% and 0% of the conventional N application rate (870 kg N ha −1  y −1 ). After six years of N fertilization, the relative abundances of Firmicutes, Acidobacteria, Betaproteobacteria and Planctomycetes, and thus the bacterial community composition, were different among the soils from each treatment. The bacterial community composition was significantly correlated with soil electrical conductivity (EC), pH, NH 4 + –N and NO 3 − –N. The bacterial OTU phylotype richness and phylogenetic diversity were generally lower in soils with higher N fertilization rates, were significantly positively correlated with soil pH and dissolved organic N, and were negatively correlated with soil EC. The results indicate that N fertilization could affect the bacterial community composition and diversity, either directly through altering soil N availability, or indirectly through altering soil EC and pH. They suggest that soil secondary salinization and acidification, brought on by high N fertilization rates, may play more important roles than previously thought in shaping the bacterial communities in intensively managed agricultural ecosystems.