Growth and nutrition of carob plants as affected by nitrogen sources

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Abstract
Carob seedlings were grown at different proportions of nitrate NO3) and ammonium (NH4) supplied at a concentration of 3.5 mM nitrogen (N). The effect of five different combinations of NH4‐ and NO3‐N on growth rates, N and carbon (C) content of the plant and dry matter distribution were studied. The presence of NH4 in the nutrient solution enhanced plant growth rate, although net photosynthesis rates per unit area were lower than in NO3‐fed plants. Nitrate‐fed plants exhibited the highest rates of carbon dioxide (CO2) assimilation, water use, and N‐use efficiency. Nevertheless, plants growing only with NO3 were more fragile and susceptible to fungus infections. The role of cotyledons on the regulation of the supply of photosynthates from leaves to roots in the different combinations of NO3 and NH4 is described. Results suggest that the growth rates of carob may be improved using suitable combinations of NO3‐ and NH4‐N. Equal concentrations of these two N sources allows good development and adequate allocation of low C and N to different developing sinks of the carob seedlings.