Abstract: [Objective] The purpose of this paper is to explore carbon density and its allocation in young plantation of Platycladus orientalis at different ages using hilly loess in Ning County of Gansu Province as the study area, with an expectation to provide the theoretical basis for evaluation on the ecological benefit of artificial forest in the hilly Loess Plateau.[Method] P. orientalis plantation at different ages of 7, 10, 12 and 14 years were used for this study. Three sample-plots were set up for every stand age, then samples were individually taken from tree, shrub, herb and litter layers, and soil was sampled at a depth of 0-100 cm in each plot. The carbon contents of plant and soil samples were determined by using elemental analyzer Liqui TOCⅡ, the carbon density and its allocation were analyzed in young plantations of P. orientalis in the hilly Loess Plateau in Gansu Province. [Result] The results showed that the carbon content in different organs of P. orientalis ranged from 447.51 to 513.93 g·kg^-1, with an order of cone > leaf > stem > thick-branch > fine-branch > fine-root > stump > bark > thick-root > large-root > medium-root > small-root. The carbon content of root was the lowest in shrub and herb layers, and the carbon content of un-decomposed layer in litter was higher than that of semi-decomposed layer. Significant difference in carbon content was observed among different layers of the ecology system of P.orientalis plantation at different ages. The carbon content in the soil layer (0-100 cm) ranged from 23.31 to 96.08 g·kg^-1, and increased with the increase of stand age but decreased with the increase of soil depth. The carbon density of the tree layer in the vegetation was higher than that of shrub, herb and litter layers. The carbon density in 0-100 cm soil layer was the largest in the ecosystem, showing significant difference with the increase of age. The carbon densities in the ecosystem of P. orientalis plantation at ages of 7, 10, 12 and 14 years were 37.56, 44.67, 50.87 and 56.34 t·hm^-2, respectively. All the carbon densities in tree, shrub, herb, humus , and soil layer increased with the increase of stand age. [Conclusion] The carbon content of tree layer of P. orientalis plantation showed significant(P<0.05)difference among organs of the trees, but no significant difference was observed for the same organ at different ages(P>0.05). Carbon stocks in different layers of the P. orientalis plantation ecosystems were found in the order of soil>tree>herb>litter>shrub. The carbon density of different layers of P. orientalis plantation increased with the increase of age, and the proportion of carbon distribution of tree, shrub, herb, and litter layers increased while that of soil layer decreased with increase of stand ages.

Key words: Platycladus orientalis, plantation, stand age, carbon density, carbon density components, the hilly loess region in Gansu Province