EFFECTS OF CALCIUM ON GROWTH AND NUTRITIONAL STATE OF CITRUS SEEDLINGS UNDER NACL STRESS

In saline conditions excessive amount of saline ions maybe absorbed by plants when the Na⁺/Ca²⁺ ratio of the root medium is high. In the experiment described seedlings of the rootstocks Carrizo citrange, Mandarino Cleopatra and Citrus macrophylla were grown in a growth chamber with Hoagland solution. Four treatments were studied: control (0 mM NaCl, 4 mM Ca²⁺), control+extra Ca (0 mM NaCl, 6 mM Ca²⁺), saline (60 mM NaCl, 4 mM Ca²⁺) and saline+extra Ca (60 mM NaCl, 6 mM Ca²⁺). Thirty days after application of the different treatments, seedling growth, mineral nutrition and physiological responses were analysed. In general, salinity decreased the weight and leaf number of all rootstocks. Regardless the saline levels, the extra Ca did not affect the growth of Carrizo plants; however, the weight of C. macrophylla plants was not diminished by salinity in treatments involving extra Ca. In saline conditions, extra Ca also increased the leaf number of C. macrophylla plants compared with the treatment without extra Ca. Nevertheless, in Cleopatra, a more salt-tolerant rootstock, treatment with extra Ca did not improve the plant weight in saline treatments. The differing salinity tolerances of the three rootstocks could explain the differences found in the growth responses to the various treatments. Under saline conditions C. macrophylla and Carrizo plants showed a much reduced water content, while extra Ca helped C. macrophylla plants to partially recover their relative water content. The application of extra Ca did not reduce the high level of Na⁺ found in the leaves of the three rootstocks but slightly decreased leaf Cl^- levels, especially in Cleopatra plants. The leaf osmotic potential of the three rootstocks significantly decreased due to the effect of salinity. Extra Ca also reduced this parameter in Carrizo and C. macrophylla plants.