Abstract: This paper studied the dynamic characteristics of K+ uptake by 5 plants and the effects of NH4+ on K+ uptake.The experiment was carried out by hydroponics and with application of ion channel inhibitor TEA at low K+ concentration. Under with or without NH4+ the dynamic parameters of +uptake were assessed.The results indicated that the K+ uptake curve by high affinity transport system for K+ (K+-HATS) in root cells could be described by the Michaelich-Menten equation.There was relatively little difference(below 50%) in Km among different plants,showing a small diversity in affinity of K+ -HATS to K+.For different plants there was significant difference in Vmax of K+-HATS,e.g.the Vmax of wheat was 11 times more than that of soybean,which indicated a great discrepancy in K+-carrier number,and this discrepancy resulted in a great diversity in K+ uptake of plants under lower K+ concentration.Ammonium could greatly decrease the rate of K+ uptake by plants.Compared with lack of NH4+the Vmax of soybean was only 20% of that under with NH4+ application.The affinity of K+-HATS of plants to K+,however,was less affected by NH4+,and reduction of Km for all plants used in this experiment was less than 10%.The results above showed that for the K+-HATS of plants the effects of NH4+on the K+ uptake were mainly due to competition of NH4+ for the K+-carrier at the cell membrane.