Objective  To explore the adaptability and mechanism of walnut under phosphorus (P) deficiency stress.

  Method  The effects of P deficiency on the growth and physiological traits of Walnut seedlings were studied with control (CK), moderate P deficiency (MP) and severe P deficiency (SP).

  Result  (1) Under the stress of P deficiency, the aboveground biomass and root biomass of walnut seedlings were significantly lower than that of CK, but the root vigor and acid phosphatase activities were higher than these of CK, and it became more severe with the increase of P deficiency; (2) under P deficiency, the contents of chlorophyll a, chlorophyll b and carotenoid, net photosynthetic rate (P_n) , stomatal conductance (G_s) and transpiration rate (T_r) in leaves of walnut seedlings were significantly lower than those of CK. In addition, the P_n increased in the middle and late processing, G_s and T_r decreased significantly after 60 days. (3) during the whole experiment, the activities of superoxide dismutase, peroxidase, catalase and the content of malondialdehyde (MDA) were the highest in CK, the next was in MP treatment, and the last was in SP treatment. However, the activities of SOD and POD, and the contents of MDA increased in the middle and late stage of P deficiency, but the contents of proline (PRO) and soluble sugar were not significantly different.

  Conclusion  The results showed that walnut could increase the input to the root by self-regulation under low P stress in order to improve the absorptive capacity. At the same time, the stress resistance can be enhanced by inhibiting the formation of photosynthetic pigment, reducing the photosynthetic capacity of leaves, and enhancing the activity of cell protective enzyme system.