Sodium and chloride are typically viewed as waste ions that plants do not need. This can be true if their levels are high in a water source, research has shown that plants do use these elements in small quantities.
Function: Sodium is not an essential element for plants but can be used in small quantities, similar to micronutrients, to aid in metabolism and synthesis of chlorophyll. In some plants, it can be used as a partial replacement for potassium and aids in the opening and closing of stomata, which helps regulate internal water balance. Chloride is needed in small quantities and aids in plant metabolism, photosynthesis, osmosis and ionic balance within the cell.
Deficiency: Sodium deficiency does not appear to exhibit any symptoms since it is not an essential element. Chloride deficiency can occur if there is consistently less than 2 ppm chloride in the growing medium and the symptoms appear as chlorotic blotches with necrotic spots located between the veins or on the margins of the young leaves. In advanced cases, chloride deficiency could cause plant wilting. Both deficiencies rarely occur since most water source provide them and fertilizers often have them as impurities.
Toxicity: Sodium toxicity appears as necrosis or scorching of the leaf and margins, similar to micronutrient toxicities. Chloride toxicity starts as premature yellowing of leaves then it leads to marginal or tip necrosis of older leaves and also bronzing.