Growth and nutrition of carob plants as affected by nitrogen sources

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.

Notes

Center for Desert Agrobiology, J. Blaustein Institute for Desert Research. Ben‐Gurion University of the Negev, Sede Boqer Israel.