To investigate differences in physiological characteristics of growth and physiological basis of high growth vigor in the first generation of Populus deltoides which are from different growth vigor clones,here we chose two groups of seedlings with different growth vigor:high(A) and low(B).Indexes of phenotype and physiology were successively measured to study the growth,photosynthesis and nutrient absorption.There were significant or very significant differences in dry mass of root,stem, leaf and the total biomass between A and B.Dry matter of roots had the smallest proportion in different components,and the largest proportion was stem in A,while the leaf had the largest proportion in B.Changes in growth and physiological characteristics showed a certain regularity during June to September.All clones grew the most rapidly and physiological characteristics varied the most significantly in July.Correlation analysis showed that seedling height and ground diameter were both significantly correlated to leaf area,night respiration rate,NH_4~- uptake rate and the total photosynthetic rate(R>0.826,P<0.05),suggesting that the seedling growth was mainly affected by their own total photosynthetic capacity,nutrient absorption and night respiration consumption.In general,A was superior to B in all these factors,which construct physiological basis of the high growth vigor. To investigate differences in physiological characteristics of growth and physiological basis of high growth vigor in the first generation of Populus deltoides which are from different growth vigor clones, here we chose two groups of seedlings with different growth vigor: high (A) and low (B Indexes of phenotype and physiology were successively measured to study the growth, photosynthesis and nutrient absorption. Here are significant or very significant differences in dry mass of root, stem, leaf and the total biomass between A and B. Dry matter of roots had the smallest proportion in different components, and the largest proportion was stem in A, while the leaf had the largest proportion in B. Changes in growth and physiological characteristics showed a certain regularity during June to September. All clones grew the most rapidly and physiological characteristics varied the most significant in July.Correlation analysis showed that seedling height and ground diameter were both significantly c suggesting that the seedling growth was mainly affected by their own total photosynthetic capacity, nutrient absorption and night respiration rate (R> 0.826, P <0.05) In general, A was superior to B in all these factors, which construct physiological basis of the high growth vigor.