Maximal biomass production can occur in corn (Zea mays) in the absence of NO3 accumulation in either leaves or roots

Abstract

In order to investigate effects of limited NO3 availability in corn (Zea mays L. cv. Brulouis) 17‐day‐old plants were grown for a further 25 days on sand in a growth chamber. The plants received frequent irrigation with a complete nutrient solution containing 0.2, 0.6, 1.5 or 3.0 mM NO3. With 0.2 mM NO; nitrate levels in both roots and leaves diminished rapidly and were almost zero after 10 days treatment. Concurrently, as signs of nitrogen deficiency appeared, shoot growth was restricted, whereas root growth was enhanced. In addition, the concentration of reduced nitrogen and malate in the leaves declined, and in vitro nitrate reductase activity (NRA. EC 1.6.6.1), soluble protein and chlorophyll levels of leaf tissue were depressed and starch concentration was enhanced. With 0.6 mM NO3 in the nutrient solution, the decrease in NO3 levels in the tissues and the increase in root development were similar to those observed with 0.2 mM NO3. However, shoot growth, reduced nitrogen concentration in leaves, and the above‐mentioned biochemical characteristics were almost identical to those obtained at 1.5 and 3.0 mM NO3. This indicates that when supplied with 0.6 mM NO3, corn plants were able to absorb sufficient NO3 to support maximal biomass production without appreciable NO3 accumulation in roots or shoot. It is, thus, suggested that the plants responded to low NO3, availability in medium by enhancing root growth and by maximizing NO3 reduction relative to NO3 accumulation.