Aluminium and ammonium ion effects on the depletion of potassium from hydroponic solutions by Trifolium repens L. cv. ‘grasslands hoia’

Abstract

The uptake of potassium from hydroponic solutions by Trifolium repens is reduced in the presence of NH₄ ⁺. However, it appears that a concurrent effect of NH₄ ⁺ is to induce, via the plant, marked changes in pH which counters the effect of NH₄ ⁺ on K uptake. When the variation in measured mean K concentration changes (KCC) associated with the variation in pH change is removed by analysis of the data using pH as a covariate, an apparent increase in K removal from solution is observed in the presence of NH₄ ⁺.

Plant‐induced changes in pH also apparently affect the Al‐NH₄ ⁺ interaction. This treatment combination induces a plant effect on the pH which in turn keeps the KCC at a fairly constant level resulting in no apparent interaction. However covariate analysis reveals the marked effect Al has on K uptake at the zero NH₄ ⁺ level. Al in the nutrient media at 148 uM causes an apparent K efflux which can not be attributed directly to variation in pH changes. When NH₄ ⁺ is present this effect is reversed.

It appears that more than one mechanism for K uptake is involved, at least one of which is not inhibited by NH₄ ⁺.

Key words:

• Aluminium ammonium potassium T. repens uptake