<p>Nitrogen (N) retained in plant and soil in late growing season is of great importance in preventing N loss and providing available N for plant growth in next early growing season in cold regions. How climatic warming changes the N retained was seldom examined. We conducted an in situ ¹⁵N labelling experiment (1) to reveal how late growing season plant and soil N retention changed and (2) to understand how competition for available N and niche partitioning between plants and microorganisms impact the N retention change in an alpine meadow warmed (1.1&#xa0;°C increase in surface soil temperature) by infrared heaters for 14 years. Results showed that N retained in both belowground biomass and in soil microorganisms increased at topsoil (0–10&#xa0;cm) under simulated warming. The competition between plants and soil microorganisms for available N in the rhizosphere of sedges, forbs, legumes and grasses showed no change. The N uptake rates of both plants and soil microorganisms also did not change with warming. Yet, niche partitioning in uptake of different available N forms (NH₄⁺-N, NO₃⁻-N, and glycine) was intensified between plants and soil microorganisms in the rhizosphere of sedges and forbs. In a warm climate, sedges increased the percentage uptake of NO₃⁻-N but forbs increased that of glycine; soil microorganisms in the rhizosphere soil of sedges increased the percentage of glycine but they took up more NO₃⁻-N in the rhizosphere soil of forbs. Niche partitioning between plants and soil microorganisms was positively related to the soil NO₃⁻-N and dissolved organic carbon content. Our results suggest that intensified chemical niche partitioning between plants and microorganisms, especially in the rhizosphere of dominant plant groups, induced improvement in ecosystem N retention, which might prevent the N loss and contribute to the increase in plant productivity in cold regions under future climatic warming.</p>