The Effects of Calcium and Magnesium Deficiency on the Growth, Physiology, and Nutrient Uptake Characteristics of Walnut Trees

Abstract

This study explored the response characteristics and adaptation mechanisms of walnut saplings under calcium and magnesium deficiency. Using walnut saplings as the research subjects, and three treatment groups were established for pot experiments: no deficiency (control, CK), calcium deficiency (–Ca), and magnesium deficiency (–Mg). The development, physiological attributes, and mineral composition of walnut seedlings were assessed, with an analysis focusing on how deficiencies in calcium and magnesium impact these elements. Compared to the findings in the CK group, walnut plant height, ground diameter, leaf area, root length, root area, number of root tips, and biomass were significantly decreased in the –Ca and –Mg groups. However, the proportions of the root surface area attributable to level I and II roots were significantly increased in the –Ca and –Mg groups, whereas that attributable to level V roots was significantly decreased. The root-to-shoot ratio was significantly increased in both groups. Peroxidase (POD), proline (Pro), and malondialdehyde (MDA) levels in walnuts significantly increased under calcium deficiency ( p <0.05), Moreover, when there is a deficiency in magnesium, there is a notable escalation in the activities of SOD, POD, and catalase, as well as a marked rise in the levels of Pro, MDA, and soluble sugars. Calcium and magnesium deficiency significantly altered mineral content of walnuts. Calcium deficiency inhibited the absorption of N, Ca, Fe, Zn, Cu, and Mn, but promoted that of P, K, and Mg. Magnesium deficiency inhibited the absorption of N, P, K, Mg, and Fe, whereas it has no effect on other minerals. Long-term calcium and magnesium deficiency significantly affected the growth of walnut saplings, with magnesium deficiency having strong effects. However, saplings adjusted to mineral deficiency by enhancing the absorption capacity of their roots. Simultaneously, They stimulated the antioxidant protection mechanisms, modulating the activity of enzymes that combat oxidation, and altering the levels of free Pro and soluble sugars within cells to eliminate free radicals generated due to stress. This, in turn, alleviates the harm caused by lipid peroxidation and bolsters resistance to adverse stress.