MINERAL NITROGEN IN PLANT PHYSIOLOGY AND PLANT NUTRITION

Nitrogen (N) nutrition enhances metabolic processes that influences th e physicochemical environment at the soil-root interface, modifies rhi zosphere conditions, interferes with the uptake of cations and anions, and enhances or represses the activity of several enzyme systems. Als o, it affects growth patterns, protein content, and protein quality of seeds. Ammonium (NH4)-N nutrition increases anion uptake, free amino- N/protein ratios, and acidity of root free space; it reduces carbohydr ate levels in plant tissues. NO3-N nutrition results in higher cation uptake, higher carbohydrate content in tissues, and alkalinization of root free space. N-Assimilation interferes with the allocation of dry matter and energy, which causes different growth rates of plant parts. In this article we review the effects of mineral-N nutrition on uptak e of cations and anions, activity of enzymes, growth patterns of roots and shoots, and water use efficiency, protein content, and protein qu ality of seeds.