Effects of supplementary potassium nitrate on growth and gas-exchange characteristics of salt-stressed citrus seedlings
2014
Khoshbakht, D. | Ghorbani, A. | Baninasab, B. | Naseri, L. A. | Mirzaei, M.
We investigated the effects of supplementary KNO₃and NaCl on one-year-old, potted Valencia orange (Citrus sinensis) scions grafted on Iranian mandarin Bakraii [Citrus reticulate × Citrus limetta] (Valencia/Bakraii) and Carrizo citrange [C. sinensis × Poncirus trifoliata] (Valencia/Carrizo) rootstocks. After watering plants for 60 days with 50 mM NaCl, the lowest reduction in dry mass, stomatal conductance, and chlorophyll (Chl) content was found in Valencia/Bakraii. Bakraii accumulated more Cl⁻and Na⁺in roots and transferred less to Valencia leaves compared with Carrizo rootstock. Moreover, higher net photosynthetic rate was found in Valencia/Bakraii than those on Carrizo rootstock. NaCl caused a decrease in the maximal efficiency of PSII photochemistry (Fᵥ/Fₘ) and effective quantum yield (ΦPSII) but elevated coefficient of nonphotochemical quenching. Salinity reduced Ca²⁺, Mg²⁺, and total N contents, and increased Na⁺/K⁺ratio in leaves and roots of both grafting combinations. Salinity increased K⁺and proline content in leaves and decreased K⁺concentrations in roots of both grafting combinations. In salinized plants, nitrate supplementation (10 mM KNO₃) reduced leaf abscission, Cl⁻, Na⁺, Na⁺/K⁺, and Ca²⁺concentrations in leaves and roots of both combinations. K⁺and N concentrations and proline increased in leaves of the nitrate-supplemented salinized plants. Supplementary nitrate increased leaf number and area, stem elongation, Chl content, Fᵥ/Fₘ, and ΦPSIIand stimulated photosynthetic activity. Thus, nitrate ameliorated the deleterious effects of NaCl stress and stimulated the plant metabolism and growth. It can be used as a vital treatment under such condition.
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