Responses of the rhizosphere microbiome to long-term nitrogen addition in a boreal forest

As the interface between plants and soil, the response of the rhizosphere to nitrogen deposition is particularly important. The rhizosphere responses to nitrogen deposition are not consistent. Here, four levels of nitrogen addition treatments were applied in boreal forests of China for 8 years: control, low nitrogen, medium nitrogen, and high nitrogen. We analyzed the soil properties and microbial communities of rhizosphere and bulk soils under different nitrogen application levels and assessed the relationship between the main species and environmental factors. The results showed that long-term nitrogen addition significantly reduced the content of total carbon in the soil and increased the soil microbial biomass nitrogen in the rhizosphere. The total carbon content in the rhizosphere under high nitrogen was 40.79 g * [kg.sup.-1], which was significantly lower than that in the control (51.82 g * [kg.sup.-1]). The diversity of the rhizosphere and bulk soil fungal communities had different significant responses to nitrogen addition. Some specific microbial taxa could be used as rhizosphere bacterial biomarkers under different nitrogen treatments. The soil microbial biomass nitrogen was the significant environmental variable affecting bacterial species variation in the rhizosphere. Nitrogen addition will change the diversity of the rhizosphere microbial community by changing soil microenvironmental factors.