Objective  The adaptive mechanism of walnut was explored under short-term potassium stress.

  Method  Walnut seedlings were treated with different levels of potassium deficiency for 75 d: control (CK), moderate potassium deficiency (MK) and severe potassium deficiency (SK), respectively. The related indexes were measured every 15 d, and the effects of potassium deficiency stress on the growth and physiology of walnut seedlings were analyzed.

  Result  (1) Under K deficiency stress, the aboveground biomass, root biomass, chlorophyll a, chlorophyll b and carotenoid contents of walnut seedlings were significantly lower than those of CK (control treatment), and the overall decrease was more obvious with the aggravation of K deficiency degree and the extension of treatment time. (2) Compared with CK treatment, F_v/F_m, Φ_PSⅡ, ETR and qP of walnut seedlings decreased significantly at the late stage of MK and SK (60−75 d). (3) As the processing time increased, CAT of walnut seedlings increased at first and then decreased under different K deficiency treatments. MK, SK and CK treatments reached the maximum at 30, 45 and 60 d, respectively. SOD activity of MK and SK increased, but POD activity decreased under severe K deficiency. From the middle stage of treatment (30 d) , the content of MDA in walnut seedlings increased with the increase of stress degree.

  Conclusion  The growth of root and aboveground parts, and the synthesis of photosynthetic pigments of walnut are significantly affected by potassium deficiency stress. However, the walnut could increase the input to root system through self-regulation to improve its absorption capacity, and consume the excess excitation energy of PSⅡ reaction center by increasing heat dissipation, in order to reduce the damage of stress on photosynthetic apparatus. Furtherly, the walnut could mobilize its enzymatic antioxidant system, and produce certain resistance to potassium deficiency stress.