Network resilience correlates with amoA gene responses to nitrogen and litter input in a desert steppe

Understanding how ammonia-oxidizing microorganisms respond to different nitrogen (N) inputs is crucial for predicting N cycling in fragile ecosystems. This study investigated the responses of ammonia-oxidizing ( amoA ) genes to mineral N addition (+N) and plant litter input (+L), along with the underlying microbial mechanisms, in an N-limited desert steppe over three consecutive years. Both + N and +L treatments significantly increased AOA- amoA abundance, with +N leading to a 164.00% increase and +L to a 58.18% increase by the third year, whereas AOB- amoA exhibited a distinct “suppression–recovery” trajectory under + N (decreasing by 53.54% in year one but ultimately exceeding the CK); litter input consistently enhanced AOB- amoA abundance by 108.71% and 85.89% in the subsequent two years. Nitrososphaerales (Group 1.1b) dominated the AOA population, whereas AOB population dynamics were largely driven by Nitrosomonas . Although diversity and network complexity correlated positively with amoA abundance, network robustness demonstrated the strongest explanatory power, emerging as a key predictor. The AOA network was closely associated with soil organic carbon (path coefficient = 0.183) and total nitrogen (path coefficient −0.385), whereas the AOB network showed a stronger relationship with inorganic nitrogen (path coefficient −0.402). These findings highlight the contrasting substrate preferences of ammonia-oxidizing microorganisms: AOA favoring low, sustained ammonium inputs from litter mineralization, and AOB responding to pulsed inorganic N enrichment. Overall, this study advances our understanding of microbially mediated ammonia oxidation in desert steppes and provides insights to guide sustainable grassland management.