Lignin is the most recalcitrant component in litter decomposition,and its degradation process serves as the rate-limiting step in the carbon cycle of terrestrial ecosystems. However,the effects of nitrogen deposition on lignin degradation rates in alpine steppe plant roots remain unclear. Utilizing a four-year nitrogen deposition simulation platform,we employed the litterbag method to examine the effects of nitrogen deposition on root litter decomposition and lignin degradation in four typical plant species of the northern Tibetan alpine steppe. The results showed that:(1) Simulated nitrogen deposition had no significant effects on the root mass loss rate or lignin degradation rate of plants in alpine steppe of northern Tibet. (2) The root litter mass loss rate progressively increased with decomposition time,while the lignin degradation rate exhibited a pattern of being initially low,increasing during the middle stage,and decreasing in the final stage of decomposition. (3) The root mass loss rate was regulated by the initial lignin/nitrogen ratio,with roots having a high initial lignin/nitrogen ratio showing significantly lower mass loss rates compared to those with lower ratios. The lignin degradation rate was regulated by the initial lignin concentration,with high-lignin roots exhibiting faster lignin degradation rates than low-lignin roots. These findings provide valuable insights into the effects of nitrogen deposition on root decomposition and material cycling in alpine grassland ecosystems.