FOLIAR AND ROOT APPLICATION OF POTASSIUM NITRATE AND CALCIUM NITRATE TO CITRUS MACROPHYLLA SEEDLINGS UNDER NACL STRESS

A growth chamber experiment was conducted to determine whether KNO₃ or Ca(NO₃)₂ could mitigate the adverse effects of salt stress on Citrus macrophylla seedlings. Six treatments were studied: C (control), S (30 mM NaCl), KR (30 mM NaCl+10 mM KNO₃ applied to the root system), KL (30 mM NaCl+10 mM KNO₃ applied to the leaves), CaR (30 mM NaCl+10 mM Ca(NO₃)₂ applied to root system) and CaL (30 mM NaCl+10 mM Ca(NO₃)₂ applied to the leaves). Although plant growth was unaffected by all the saline treatments, salt injury in the form of leaf burn was observed. Salinity also affected leaf gas exchange parameters, which decreased with the application of 30 mM NaCl. The potassium and calcium applications did not lead to increased photosynthesis rate. Neither the Ca nor the K treatment reduced the high Cl levels in the leaves, and leaf Na was only reduced by the CaR treatment. The calcium levels in leaves following the CaR treatment were higher than in C plants, whereas the CaL, KR and KL treatments led to lower Ca levels than in C plants. This was also the case with membrane stability, which increased with CaR but not with the foliar application of Ca or either of the K treatments. Cellular damage produced by salinity decreased with KL and both Ca treatments. These results suggest that, in general, the adverse effects of salinity on the nutritional and physiological response of C. macrophylla are not alleviated by the foliar treatments of Ca and K applied in this experiment.