Physiological and anatomical disturbances induced by chloride salts in sensitive and tolerant citrus: beneficial and detrimental effects of cations
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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) CaCl(2), 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, Ca(2+) was more beneficial, and K(+) more detrimental, for growth than sodium. Photosynthesis and growth disturbances were highly correlated (P less than or equal to 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 CT build-up and reduced growth, whereas chloride correlations with declines in photosynthesis or increases in succulence appear to be indirect.