Responses of soil biological traits and bacterial communities to nitrogen fertilization mediate maize yields across three soil types

Although the effects of nitrogen (N) fertilization on soil microflora have been well studied, the effects should be verified across soil types and N-added levels. To understand the impacts of N fertilization on shifts in soil biological traits and bacterial communities and to further explore the coupling mediation of these parameters with respect to crop yields, we sampled soils from three experimental sites (each site received three levels of N fertilization (0, 168 and 312 kg N ha−1)) that share the same climatic conditions but have different soil types (clay, alluvial and sandy soils). In clay and sandy soils, total microbial biomass with N fertilization treatments was lower than that with no treatment, and the N and carbon (C) contents of microbial biomass with N fertilization treatments were higher than those without treatment. In alluvial soils, these properties were higher with N fertilization treatment than with no treatment. Together with N addition, bacterial abundance and phylogenetic diversity significantly decreased in alluvial and sandy soils. Soil type had a higher (38.82%, p < 0.001) individual impact on bacterial community structure than did N fertilization (18.92%, p < 0.001). Interactions between soil type and N fertilization also notably explained 11.08% of the altered community structure. Overall, N fertilization significantly affected soil physicochemical (such as pH, organic C and NO3--N) and biological properties (microbial biomass C and N), which can affect maize yield directly and indirectly by further mediating soil bacterial abundance, diversity and community structure, with consequences for crop production. Bacterial community structure (path coefficient = 0.64) had the most positive and direct impact on maize yield, followed by organic C (0.37) and available N (0.33). Altogether, these findings suggest that N fertilization affects soil biological traits and bacterial communities across different soil types. Further understanding these soil microbial parameters can contribute to crop yield and may provide deeper insight into predicting the coupling of soil functionality and crop productivity.