Abstract: Through the measurement of organs carbon content rate,the study was conducted on distribution of carbon content rate under different organs of different species and same tree species in the plant communities of Fraxinus mandschurica Rupr,Quercus mongolica Fisch.ex Turcz,and Ulums macrocarpa Hance in Daqinggou of Horqin.The results were as follows:(1)The different aged branches of Ulums macrocarpa Hance.and Quercus mongolica Fisch.ex Turcz.carbon content rate range difference are maximum(2.46%),three tree species carbon content rate of different aged branches present significant differences.(2)Three tree species carbon content rate of different thickness roots are different,in the average the root carbon content rate of Quercus mongolica Fisch.ex Turcz.(50.6%)higher than in the average the roots carbon content rate of Ulums macrocarpa Hance.(46.42%)and Fraxinus mandschurica Rupr.(46.25%).(3)Fraxinus mandschurica Rupr.Quercus mongolica Fisch.ex Turcz.and Ulums macrocarpa Hance.,three tree species organ carbon content varied between 48.17% and 53.92%,45.58% and 51.44% and 46.25% and 51.68%.Thus,different species carbon content rate due to the impact from genetic factors,even if the different organs of the same species carbon content rate are also different because of the carbon content、organ composition and organ growth years.

Key words: Fraxinus mandschurica Rupr, Quercus mongolica Fisch.ex Turcz, Ulums macrocarpa Hance, carbon content rate, Daqinggou