Growth and ammonium:Nitrate uptake ratio of spring wheat cultivars under a homogeneous and a spatially separated supply of ammonium and nitrate

Abstract

In a split‐root experiment, seedlings of two German spring wheat cultivars (Remus, Star) were grown hydroponically to investigate the effect of a homogeneous and a spatially separated supply of ammonium (NH₄) and nitrate (NO₃) (HS and SS, respectively) on the production and distribution of dry matter, and on the uptake of NH₄ and NO₃. Under HS, both halves of the seminal root system were exposed to a 1:1 mixture of NH₄‐N and NO₃‐N. At SS, one half of the seminal root system was fed with NH₄, while the other half received NO₃. The pH of the nutrient solutions was 6.5, and the nitrogen (N) concentration was 3 mM in all compartments. Plants grown under HS produced more shoot dry matter, and showed a higher concentration of N in the shoots and a higher NH₄‐N: NO₃‐N uptake ratio, while root dry matter and the root:shoot dry matter ratio were greater at SS. Irrespective of N form localization, cv. Star clearly favoured NH₄ as source of N, while cv. Remus exhibited a more balanced NH₄‐N: NO₃‐N uptake ratio. Under SS, the contribution of the compartment supplied with NH₄ to seminal root dry matter production and total water consumption was significantly greater for cv. Star than for cv. Remus. A supplementary experiment showed that cv. Star had lower levels of nitrate reductase activity and lower concentrations of NO₃ in the shoots than did cv. Remus.