INFLUENCE OF POTASSIUM SUPPLY ON UPTAKE A ND ASSIMILATION OF (N-15)-NITRATE AND (N-15)-AMMONIUM IN SCOTS PINE (PINUS-SYLVESTRIS) SEEDLINGS

In the present study with Scots pine seedlings the interaction between nitrate/ammonium - and potassium nutrition was studied with the help of labelled nitrogen (N-15). The major results are as follows: The see dlings absorb ammonium much more readily than nitrate. Optimum potassi um supply leads to a higher protein content. This effect is to be attr ibuted to an increased assimilation of nitrate and endogenous N-storag e compounds. Potassium stimulated protein synthesis corresponds with a decrease of soluble N-containing compounds. Reduced potassium supply leads to the consequence that the additionally absorbed ammonium is in corporated in soluble N-containing compounds. The previously described alleviating effect of potassium on ammonium stress in coniferous seed lings is explained by the potassium mediated decrease of ammonium inco rporation.-While uptake of nitrate is independent of potassium supply, ammonium uptake is reduced in the presence of potassium.