Physiological and anatomical disturbances induced by chloride salts in sensitive and tolerant citrus: beneficial and detrimental effects of cations

Abstract

In citrus, the relative contributions of chloride and cations to growth disturbances induced by salinity are a matter of controversy. Chloride salts (15 mol m–3 CaCl2, 30 mol m–3 CaCl and 30 mol m–3 KCl) reduced growth and gas exchange parameters, increased leaf damage and abscission and produced anatomical disarrangements and mineral imbalances in seedlings of sensitive Carrizo citrange (Citrus sinensis x Poncirus trifoliata) and tolerant Cleopatra mandarin (Citrus reshni). In both cultivars, Ca2+ was more beneficial, and K+ more detrimental, for growth than sodium. Photosynthesis and growth disturbances were highly correlated (P≤ 0·001) with leaf Cl– build‐up. In the sensitive genotype, Cl– was also significantly correlated with several leaf anatomical disarrangements, such as increase in succulence. In comparison with sodium, both calcium and potassium increased leaf Cl– content (up to 25 and 69%, respectively). Protective calcium effects were not linked to improvement of photosynthesis, reduction of leaf anatomical disarrangements, or prevention of Cl– and Na+ increases. It is proposed that the ameliorative effects of calcium on citrus grown under salinity are mostly related to reduction of leaf abscission. Collectively, the data suggest a cause–effect relationship between Cl– build‐up and reduced growth, whereas chloride correlations with declines in photosynthesis or increases in succulence appear to be indirect.