Nitrogen leaching greatly impacts bacterial community and denitrifiers abundance in subsoil under long-term fertilization

Soil microbes represent one of the most important members of agricultural systems, and many achievements about the variation of microbiota in topsoil under diverse fertilization regimes have been acquired. However, how long-term fertilization regulate microbial communities in subsoil is rarely studied. In our current research, the variation of bacterial communities in soil profiles (0–100 cm) under two typical fertilization regimes, chemical fertilization (NPK) and chemical fertilization with straw turnover (NPKS), and one no fertilization treatment (Control) were explored using high-throughput sequencing. The results showed that fertilization gave rise to greater effect on bacterial communities in topsoil (0–30 cm) than in subsoil (30–100 cm), which is consistentwith the impact on soil properties, and total nitrogen (TN) showed the highest correlation with the vertical separation of bacterial communities. Fertilization significantly decreased the bacterial richness in surface soil (0–10 cm), increased the bacterial richness in soil from 50 to 100 cm, while had little impact on the bacterial richness in soil from 10 to 50 cm. For surface soil (0–10 cm), the bacterial communities were mostly correlated with electrical conductivity (EC), whereas the bacterial communities in soil below 10 cm showed a highest correlation with nitrate. QPCR revealed that topsoil harbored a greater abundance of denitrifiers than subsoil. Fertilization enriched denitrifiers in most soil layers in the profile. However, the increase in the range of de-nitrifier abundance did not reach the increase in the range of nitrate. Further analysis found that denitrifier abundance was most positively correlated with soil organic carbon, indicating that the carbon-limit restricts the growth of denitrifiers in subsoil. These results reveal that the vertical separation of bacterial communities is largely controlled by soil resource partitioning, and nitrate leaching greatly contributes to shaping bacterial communities in subsoil in intensive agricultural systems, and further suggest that the impact of long-term fertilization on some microbial functions may be greater in subsoil than in topsoil.