Abstract: In order to explore the mechanism of interclonal differences of poplar in P efficiency and to find out a new way in breeding improved variety of poplar, phosphate uptake characteristics of kinetics and the relation between the kinetic characteristics and P efficiency were conducted by the method of solution culture with long term absorption by intact plants for poplar seedling in greenhouse. The results showed that the root uptakes of phosphate were obviously stronger in clone S₁₇, S₁₉, and 105, which were attested as high P efficiency, than in clone 106, 797, I-69, 1388, and 3244, which were low P efficiency clones. The values of K_m, the Michaelis constant, which is the concentration where influx is half of V_max, and C_min, the critical concentration, the ion concentration in solution below which net influx of the ion ceases, of S₁₇, S₁₉, and 105 were much smaller than those of other five clones, respectively. This indicated that clones of high P efficiency were much stronger than those of low P efficiency in the affinity of root system to phosphate and in tolerating P deficiency. As a result of P deficiency stress such affinities were increased over 20% for the clones of high P efficiency but below 5% for the clones of low P efficiency, as indicated by the values of K m under two P treatments. Similarly, as showed by the values of C_min, the tolerance to P deficiency stress was raised more than 85% for the clones of high P efficiency but less than 15% for the clones of low P efficiency. Consequently, variation in P uptake characteristic parameters of kinetics by root systems of various poplar clones was one of important mechanisms for the interclonal difference in P efficiency, and will probably be of great significance in breeding improved poplar variety in the future. Further more studies were needed to explain the difference of phosphorus efficiency by the index of V_max.

Key words: Poplar, Clone, Phosphorus efficiency, Phosphate uptake kinetics