To explore the effects of nitrogen deposition and precipitation changes on the soil ammonia-oxidizing bacteria(AOB)community,we conducted a split-plot experiment in a desert steppe dominated by Stipabreviflora.The main plots include three water regimes:natural rainfall(CK),a 30％increase in rainfall(W),and a 30％decrease in rainfall(R).The subplots were treated with four nitrogen levels:0(N0/CK),30(N30),50(N50),and 100(N100)kg/(hm2·a).High-throughput sequencing was utilized to assess the diversity and composition of the soil AOB community.Our findings revealed that the dominant AOB in the desert steppe soils are norank_d_Bacteria,unclassified_k_norank_d_Bacteria,and the genus Nitrosospira.Under natural rainfall conditions,the AOB-amoA gene copy number increased with higher nitrogen application.However,in the reduced rainfall treatment,the AOB-amoA gene copy number significantly rose at the N50 level but sharply declined at the N100 level,suggesting that N50 is a threshold for soil AOB abundance in the desert steppe.Furthermore,higher alpha diversity was associated with increased rainfall.Significant differences in soil AOB community structure across the various nitrogen treatments were revealed by principal coordinate analysis.Redundancy analysis identified soil moisture content,nitrate nitrogen,ammonium nitrogen,and total nitrogen as the key environmental factors driving changes of the soil AOB community.
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