The photosynthetic characteristics, nitrogen (N) transport and root-zone volumes of Forsythia suspensa seedlings cultivated in a plant growth chamber with different N concentration treatments were studied. The results showed that the dry weights of shoots and roots of Forsythia suspensa seedlings under low N treatment were higher than that under high N treatment. The effects of root restriction on the shoot and root dry weights of Forsythia suspensa seedlings under low N treatment were different, and the seedlings with low root restriction (LR, 10cm×10cm×15cm) had lower shoot and root dry weights than that with high root restriction (HR, 20cm×10cm×15cm). The net photosynthetic rate (P_n) and chlorophyll content of Forsythia suspensa seedlings under low N treatment were higher than that under high N treatment. Under low N treatment, the LR seedlings had higher P_n and stomatal conductance (G_s) than HR seedlings, however, the HR seedlings under high N treatment had higher P_n and Gs than LR seedlings. The effects of root restriction on chlorophyll content of Forsythia suspensa seedlings under both N treatments were different from that on P_n Comparatively, the maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency of PSⅡ (Ф_PSⅡ) and non-photochemical quenching coefficient (qNP) of Forsythia suspensa seedlings under low N treatment were higher than that under high N treatment. And the LR seedlings under low or high N treatment had higher Fv/Fm and qNP but lower Ф_PSⅡ and photochemical quenching coefficient (qP) than HR seedlings. The N contents in roots and shoots of Forsythia suspensa seedlings under low N treatment were lower than that under high N treatment. And the LR seedlings under low or high N treatment had lower N contents in roots and shoots than HR seedlings. The percentages of 15N allocation in roots and leaves of Forsythia suspensa seedlings under low N treatment were lower than that under high N treatment, however, the percentages of ¹⁵N allocation in branches and stems of seedlings under low N treatment were higher than that under high N treatment. The allocation percentages of N absorbed by roots in leaves and branches were 7%-10% and 7%-12% respectively, and the nitrogen demand for leave and branches growth was mainly met by internal N stocks.