Aims <p>Nitrogen (N) addition profoundly alters soil N-cycle processes in grassland ecosystems. However, it still remains unclear about the mechanisms underlying plant-microbial interactions that drive differences in N transformation between bulk and rhizosphere soils in response to N addition.</p> Methods <p>Our research examined soil N transformations under N addition using a field experiment in a natural grassland on the Loess Plateau. The treatments consisted of three levels of N addition (0, 3, and 9&#xa0;g N m⁻²&#xa0;yr⁻¹; labeled N0, N3, and N9) applied for 8&#xa0;years.</p> Results <p>The N9 addition significantly enhanced the net nitrification rate (NNR) by 73.9% compared with that of the N0 addition in bulk soil, whereas N3 and N9 additions increased the net mineralization rate (NMinR) by 33.5% and 39.6%, respectively. In rhizosphere soil, N3 and N9 additions significantly increased NNR by 89.1% and 82.6%, respectively, whereas N9 addition significantly increased NMinR by 42.5%. Root exudation, particularly amino acids such as asparagine and ornithine, was significantly correlated with N-cycle functional genes, particularly organic N metabolism genes (<i>gltB</i>, <i>gltD</i>, <i>gdhA</i>, <i>gdhB</i>, and <i>glnA</i>). N addition primarily stimulated the root exudates, <i>e.g.,</i> octanal, ornithine, and asparagine, promoting the N-cycle functional genes abundance, which subsequently accelerated the N transformation rates in rhizosphere soil.</p> Conclusions <p>Overall, this study revealed that N transformation differed between bulk and rhizosphere soils of grassland under N addition, emphasizing the need for future studies on the effects of root exudates.</p> Graphical abstract <p></p>