Potassium,calcium and magnesium antagonism in clones of Populus trichocarpa

Two clones of Populus trichocarpa varying in growth rate were grown in nutrient solutions with a range of K supply. In the leaves an antagonism between the levels of K and Ca+Mg was found, this was most extreme in the older leaves. Analysis of the contents of these elements in leaf vacuoles and cytoplasm suggests that in the vacuoles the total contents of K+Ca+Mg are controlled to maintain ionic and osmotic balance. At low K supply, the K deficit in the cytoplasm is not balance by accumulation of Ca and Mg, and it is suggested that other organic osmotica may accumulate. The regulation of K+Mg+Ca supplied to the leaves seems to be regulated by the roots and is not simple competition of ions for uptake sites at the plasmalemma.