¹⁵N-labell fertilizer was used to study on N competition between tree and peanuts,and to test the potential of tree roots acting as safety-net on Choerospondias axillaris cropped with peanut(Arachis hypogaea) in subtropical China.Five-year-old and nine-yea-rold Choerospondias axillaris recovered 9.66% and 30.15% of the N applied at topsoil of peanut area,respectively.Compared with sole peanut system,N recovery by peanut was decreased by 37.8%in 5-year-old and 59.1% in 9-yea-rold Choerospondias axillaris alley cropping system,respectively.The role of 5-yea-rold Choerospondias axillaris acting as a safetynet was not obvious,since it recovered little N from subsoil and did not decrease N residual in the soils. With increasing tree age,9-yea-rold Choerospondias axillaris showed its potential to act as a safety-net, since it recovered 33.79% N from 35cm soil layer and 14.74% N from 55 cm soil layer,respectively,and N residual in 0~60 cm soil layer was decreased by 24.1%,compared with that in sole peanut system.