Abstract: Comparison of N,Pand Kconcentrations in live and dead fine roots of Cunninghamia lanceolata,Alnus cremastogyne and Kalopanax septemlobum showed that the fine roots of A. cremastogyne had a stronger ability of Nretranslocation than K.septemlobum's, but no N translocation occurred in C.lanceolata's. P retranslocation could be found in the fine roots of the all test tree species except C.lanceolata.As for K,it could translocate from fine roots to tree bodies of all these tree species before senescence.Based on the analysis on the difference of N,P,and K concentrations in live fine roots of each pair of tree species in the mixtures,it was suggested that N and K could respectively transfer from the root system of A.cremastogyne and K. septemlobum to the fine roots of C.lanceolata,and the mechanism could be clarified through exploring the ecological process of root-soil interface.