[Interannual variations in natural abundance of nitrogen stable isotopes in soil and plant and their implications in a meadow steppe].

Nitrogen is the most limiting nutrient for ecosystems. The natural abundance of δN (N/N) can efficiently indicate ecosystem nitrogen cycling processes. We investigated the interannual variations in natural abundance of δN in soil-plant system and soil net nitrogen mineralization in a meadow steppe of Inner Mongolia. Results across the four sampling years (2017-2020) showed that the content of soil NO-N (9.83-14.79 mg·kg) was significantly higher than that of NH-N (3.92-5.00 mg·kg) and that δN value of soil NH (13.3‰-18.3‰) was significantly higher than that of NO(3.76‰-6.14‰). The δN value of soil NO was negatively correlated with soil NO content. The δN value of soil NH was relatively higher in the dry years, while the δN value of soil NO significantly decreased in the wetter and drier years. Soil net mineralization and ammonification rates were significantly higher in the dry years than that of the wet years, while soil nitrification rates showed no correlation with annual precipitation. The δN values of plants were not related to that of soils, but nega-tively correlated with plant nitrogen content. Both δN values and nitrogen contents were significantly and positively correlated between the leguminous and non-leguminous plants, suggesting that legume could facilitate nitrogen uptake of non-leguminous plants. These results could provide supporting data for nitrogen cycling and their responses to changes in precipitation in grassland soil-plant systems.