Salinity and nitrogen fertilization and nitrogen metabolism in rose plants

Abstract

Rose production is limited by salinity and highly affected by the nitrogen source present in the nutrient solution. The influence of sodium on several aspects of nutrition has been investigated in ‘Lambada' rose plants using different sources of nitrogen in the fertilization treatment. Experiments using a previously defined mono-shoot model plant and a simplified hydroponic culture allowed us to study the effects of salinity v. nitrogen on NPK uptake during the culture period. Mineral concentrations, nitrate reductase (NR) and glutamine synthetase (GS) activities were also analysed. This study showed that rose plants were more sensitive to saline conditions under NH₄⁺ fertilization without detectable effects on growth or in NPK mineral contents in shoots. Parameters affected most were enzymatic activities analysed such as leaf nitrate reductase activity which was reduced under NH₄⁺ nutrition. Leaf glutamine synthetase was also enhanced by saline conditions. The Na/K ratio showed that under NH₄⁺ nutrition, the highest sodium accumulation occurred in roots. Nitrate uptake did not show a clear pattern related to nitrogen source, however, ammonium uptake was affected by salinity when NH₄⁺ was the sole nitrogen source in the nutrient solution. Potassium and phosphate uptake were always lower when NH₄⁺ was present in the nutrient solution.