Objective Atmospheric nitrogen deposition is profoundly altering ecological processes in terrestrial ecosystems. Elucidating the mechanisms of soil microbial communities responding to the increased nitrogen deposition and how this affects the growth of desert plant communities were crucial for predicting and addressing the responses of desert ecosystems under global change.

Method This study conducted a three-year in-situ observation experiment in a desert ecosystem, establishing nitrogen addition gradients. Phospholipid fatty acid (PLFA) analysis was used to examine changes in soil microbial community structure, combined with measurements of soil physicochemical properties and plant biomass, to investigate the response patterns of soil microbial communities and systematically reveal the mechanisms of the increased nitrogen deposition affecting soil microbial communities and plant growth.

Result ① Increased nitrogen deposition significantly affected soil physicochemical properties: with the increasing nitrogen deposition, soil pH decreased from 8.64 (N₀) to 8.35 (N₈), and soil nutrients showed an increasing trend. Under the N8 treatment, soil organic carbon (SOC), total nitrogen (TN), nitrate nitrogen (NO₃⁻-N), ammonium nitrogen (NH₄ ⁺ -N), and available phosphorus (Olsen-P) increased significantly by 11.1%, 13.3%, 625.9%, 128.1% and 44.9%, respectively. ② Different soil microbial groups responded differently to increased nitrogen deposition: under high nitrogen treatment (N₈), Actinomycetes (Act), Gram-positive bacteria (G ⁺ ), and Gram-negative bacteria (G⁻) increased significantly by 34.9%, 33.2% and 27.0%, respectively. However, the increased nitrogen deposition did not alter soil microbial community structure and diversity indices. ③ Redundancy analysis indicated that soil pH, TN, and SOC were the main factors influencing the soil microbial community. Random forest results showed that dark septate endophytes (DSE) were the primary soil microbial group affecting desert plant growth. Structural equation modeling further indicated that increased nitrogen deposition regulates the soil microbial community by reducing soil pH. The decrease in pH promoted the growth of DSE, and the increase in DSE significantly inhibited plant growth. However, nitrogen addition promoted an increase in total plant community biomass.

Conclusion This study reveals the mechanism of the increased nitrogen deposition regulates the growth of soil functional microorganisms by lowering soil pH, inhibiting the growth of Erodium oxyrhinchum and promoting an increase in community biomass.