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Seasonal and microhabitat variations of chemical constituents of foliar organic carbon(C),total nitrogen(N),total phosphorus(P),and total potassium(K),in Populus euphratica growing in desert riparian forests in northwestem China and their correlations were studied.Results show that ranges of C,N,P and K contents in the leaves of P.euphratica were 39.08％-46.16％,0.28％-2.81％,0.05％-0.18％ and 0.35％-2.03％,with means of 43.51％,1.49％,0.102％ and 1.17％,respectively.The ratio of C/N,C/P and N/Pchanged from 16.26 to 146.61,from 258.08 to 908.67 and from 2.89 to 26.67;the mean was 37.24,466.27 and 15.14,respectively.The mean N content was significantly lower than of deciduous trees in China,but the mean P content was nearly equivalent.The ratio of C/N was remarkably higher than of global land plants.The ratio of N/P indicated that growth of P.euphratica was jointly limited by N and P nutrient deficiency.During the growth season,total trends of leaf C,N,P and K contents decreased.The maximum appeared in May,and the minimum in September.Among microhabitats,C,N and K contents gradually increased from riparian lowland,flatland,sandpile,Gobi and dune,but C/N ratio was opposite,and P content was not apparent.Foliar C content was extremely,significantly and positively correlated with N and K contents,respectively.The relationships of N-K and P-K were both significantly positive.