Potassium and Phosphorus

Abstract

Using an ion depletion technique, a kinetic study of K uptake by Alligator alternanthera [Alternanthera philoxeroides (Mart.) Griseb] was carried out. Potassium uptake parameters of the plant at different ages were obtained and the influences of NH₄ ⁺ and Na⁺ on the absorption of K⁺ were investigated.

In the present research, it was observed that the roots of plants which had been selected as K‐rich had a strong affinity for K⁺. With increasing plant age there was a small reduction in Imax and a slow ascension in Km. Plants grown for periods up to 120–180 days in culture solution had an Imax of 1.8–2.1 μmol Kg^‐1FWxh^‐1; with a Km value of only 8.0–14.0 μM, and Cmin below 1.0 μM. Potassium absorption was significantly inhibited by both NH₄ ⁺ and Na⁺ _, but compared with Na⁺, NH₄ ⁺ had a much stronger effect. The relative K⁺ uptake rate was reduced by over 50% when the concentration of NH₄ ⁺ in solution was 100 μM or more, however, Na⁺ showed no significant inhibition when its concentration was within 500 μM. This implies that NH₄ ⁺‐K⁺ and Na⁺‐K⁺ interactions may have different mechanisms.

Key words:

• Alligator alternanthera
• kinetics
• potassium uptake