Abstract: To explore the effects of potassium on ammonium stress, wheat seedlings cultivated with nitrate (${\text{NO}}_3^{-}-\text{N}$) or ammonium (${\text{NH}}_4^{+}-\text{N}$) nitrogen were treated with different potassium levels (low, 1 mmol·L^-1; normal, 3 mmol·L^-1; high, 6 mmol·L^-1). It was shown that compared with ${\text{NO}}_3^{-}-\text{N}$, ${\text{NH}}_4^{+}-\text{N}$ significantly (P<0.05) increased ${\text{NH}}_4^{+}$ concentration in the plants (including root and leaf), and root growth was inhibited as the total root length, root surface area and root volume were significantly (P<0.05) reduced under the same potassium level. With the increasing K dose, the root inhibition was relieved. Under ${\text{NH}}_4^{+}-\text{N}$ conditions, leaf area, stomatal conductance, and net photosynthetic rate were increased with the increasing K dose, which resulted in the significantly (P<0.05) increased soluble sugar content in leaf and root, and thus could provide more carbon skeleton for ${\text{NH}}_4^{+}$ assimilation. Meanwhile, higher potassium siginificantly (P<0.05) increased the activity of sucrose phosphate synthetase (SPS) activity in leaves. In addition, the indole-3-acetic (IAA) concentration and the ratio of IAA to cytokinin (CTK) in root increased with the increasing K dose. It was inferred that, under ${\text{NH}}_4^{+}-\text{N}$ condition, the exogenous application of potassium enhanced the capability of wheat photosynthesis, provided more carbon skeleton for ${\text{NH}}_4^{+}$ assimilation, promoted the hormone balance in roots, thus reduced the accumulation of ${\text{NH}}_4^{+}$ in plant and alleviated root inhibition.

Key words: wheat, ammonium stress, potassium, phytohormone, carbon transport