Growth and Mineral Nutrition Are Affected by Substrate Type and Salt Stress in Seedlings of Two Contrasting Citrus Rootstocks

We evaluated plant growth and leaf and root mineral nutrient responses to salinity of two-month-old citrus rootstock seedlings growing in four types of container growth media: aerated hydroponic solution, river washed sand, perlite, or a native clay-loam soil. Seedlings of Cleopatra mandarin (Citrus reticulata Blanco; Cleo, relatively salt tolerant) and Carrizo citrange [C. sinensis (L.) Osb. Poncirus trifoliate L.; Carr, salt sensitive] were grown in a controlled-environment chamber using Hoagland's nutrient solution containing either 0 mM (Control) or 50 mM sodium chloride (NaCl; salt). Without salt, seedlings in solution culture and sand grew the most and seedlings in perlite and clay-loam grew the least. The salinity treatment decreased growth in both Cleo and Carr seedlings in solution and sand but not in smaller seedlings in perlite and clay-loam soil. Cleo seedlings had lower leaf chloride (Cl−) concentration and higher leaf sodium (Na+) concentration than Carr seedlings. In the salinized clay-loam soil, Cl− and Na+ concentrations tended to be highest in leaves but lowest in roots. Salt treatment generally reduced leaf calcium (Ca2+) concentration in Cleo seedlings in all substrates and in Carr seedlings in solution and perlite. Based on total plant dry weight, seedlings grown in solution culture and sand were more salt tolerant than those grown in perlite and clay-loam soil. Since the reduced growth in clay-loam soil and perlite negated the effects of the salt treatment, salt tolerance was not linked to leaf Cl− concentration.