Characteristics of soil organic carbon in Populus davidiana natural secondary forest stands at different ages in Liaoheyuan Nature Reserve

【Objective】This study researched the soil organic carbon density and vertical distribution at depth of 0-100 cm in Populus davidiana natural secondary forests at 3different ages in Liaoheyuan Nature Reserve to provide reference for evaluating forest carbon sequestration.【Method】Soil samples were collected from 27profiles(at depth of 0-100cm)of P.davidiana natural secondary forest plantations at different ages in Liaoheyuan Nature Reserve and the soil bulk density,soil organic,and carbon soil carbon density were measured.Correlation analysis were also conducted between soil organic carbon and other soilphysical and chemical indexes.【Result】The soil bulk density in layer of 0-100 cm were 1.07-1.69g/cm3 and gradually increased with the increase of soil depth.The soil organic carbon contents in P.davidiana natural secondary forests at different ages were 1.53-17.59g/kg and decreased with the increase of soil depth.The average soil organic carbon density in layer of 0-100 cm was 15.31t/hm2,soil organic carbon densities in different soil types at same tree age increased first and then decreased gradually along with depth.Correlation analysis showed that the soil organic carbon in forests at 3different ages in the profiles had extremely positive correlation with soil total N and soil total P and positive correlation with soil pH.The soil organic carbon of middle-aged forest and nearly mature forest had extremely negative correlation with soil bulk density and soil total K but extremely positive correlation with soil moisture.The soil organic carbon of mature forest had negative correlation with soil bulk density and total K but positive correlation with soil moisture.【Conclusion】The soil organic carbon densities in depth of 0-10 cm in P.davidiana natural secondary forests at different ages were in the decreasing order of mature forestmiddle-aged forestmature forest,in the depth of 10-20 cm the order was mature forestmature forestmiddle-aged forest,and in depth of 20-100 cm the order was mature forestmiddle-aged forestnearly mature forest.