Root morphology of maize under homogeneous or spatially separated supply of ammonium and nitrate at three concentration ratios

Abstract

Maize (Zea mays L. cv. Anjou 256) seedlings were grown hydroponically for 10 d in a split-root system (3mM N; pH 5.5) under either a homogeneous supply (HS) or a simultaneous, but spatially separated supply (SS) of NH 4 + and No 3 - . Treatments comprised three NH 4 + :NO 3 - ratios (1:4, 1:1,4:1). Shoot dry matter and various root traits (dry matter, number of laterals, length of main axes, total root length and total root surface area) were determined. For all NH 4 + :NO 3 - ratios, shoot dry matter, root dry matter, total root length, and root surface area, were greater under HS than under SS. Under both SS and HS, increasing NH 4 + :NO 3 - ratios resulted in decreased shoot and root dry matter production, but did not alter the shoot:root dry matter ratio. Under SS, root dry matter, root length, and root surface area was greater on the N0 3 - -fertilized side than on the NH 4 + -fertilized side. The allocation of root dry matter, root length, and root surface area to the NH 4 + or NO 3 - compartments was unaffected by changes in the NH 4 + :NO 3 - ratio. Enhanced NH 4 + nutrition has detrimental effects on top growth, but roots are apparently unable to avoid excessive NH 4 + uptake by proliferating in zones where N0 3 - is the only form of N.