Objective  This paper studies the phenotypic characteristics, growth and physiological characteristics of walnut seedlings under different nutrient deficiency conditions, so as to provide a theoretical basis for scientific and efficient management of walnut seedlings.

  Method  Pot experiment was conducted to study the phenotypic characteristics and growth physiological changes of walnut seedlings deficient in N, P, K, Ca and Mg.

  Result  (1) The leaf symptoms and occurrence time of walnut seedlings with different element deficiency treatments were different. Among them, the symptom of N deficiency appeared the earliest, Mg deficiency followed, and K deficiency appeared the latest. The aboveground biomass of seedlings lacking N and Mg decreased by 66.5% and 48.6%, respectively compared with CK, and root biomass decreased by 48.0% and 55.0%, respectively compared with CK; (2) The photosynthetic pigment content, net photosynthetic rate and stomatal conductance of walnut seedlings treated with element deficiency were significantly lower than those of CK. Among them, the photosynthetic pigment content of seedlings lacking N and Mg decreased the most, and the net photosynthetic rate and stomatal conductance of walnut seedlings lacking Ca and Mg decreased the most; (3) The chlorophyll fluorescence parameters of walnut seedlings treated with element deficiency showed significant differences, but in general, the chlorophyll fluorescence parameters of each element deficiency treatment were different. The values of Φ_PSII, ETR, F_v/F_m and qP were significantly lower than those of CK, and the value of NPQ was significantly higher than that of CK, among which the change of P-deficient treatment was the most obvious; (4) The contents of IAA and ABA in walnut seedlings treated with element deficiency were significantly higher than those of CK, while the contents of Spm and Spd were significantly lower than those of CK, especially in N deficiency treatment.

  Conclusion  Element deficiency has certain effects on photosynthetic efficiency and endogenous hormones of seedlings, and the effects of N deficiency, Mg deficiency and Ca deficiency are the most obvious. Therefore, in the management of walnut seedlings, we should pay attention to the observation of seedling growth, diagnose and identify the deficiency of elements as soon as possible, especially N, Ca and Mg elements that are easy to appear and have obvious symptoms, and supplement them in time, so as to improve the seedling quality of walnut.