The Variation Of Distribution Characteristics And Major Fractions Of Soil Organic Carbon Under Different Forest Types In The Qinling Mountains

Adopting field investigation and indoor analysis methods, the distribution patterns of soil organic carbon, total nitrogen, soil active organic carbon and soil carbon storage in the soil profiles of Quercus aliena var acuteserrata forest(Ma Toutan forest), Pinus tabulaeformis Carr forest, Pinus armandii Franch forest, pine-oak mixed forest, Picea asperata Mast forest, and Quercus aliena var. acuteserrata forest(Xin Jiashan forest) of Qinling Mountains were studied in this paper. We wish to provide basic data for the future study of direct carbon storage of forest ecological system in Qinling Mountains area, and provide the basis for the operation and management of forest soil carbon in the area. The results show that:1. There were highly significant positive correlations between SOC and TN and the contents of SOC, TN of different soil layers decreased with increasing soil depth on all of the six soil profiles. The SOC and TN content change intervals of the six forest soils were 13.46 g?kg-1-26.41 g?kg-1 and 4.47 g?kg-1-9.51 g?kg-1, respectively, and the order of them both were Picea asperata Mast forest>pine-oak mixed forest>Quercus aliena var acuteserrata forest(Matoutan forest)>Pinus tabulaeformis Carr forest>Pinus armandii Franch forest>Quercus aliena var. acuteserrata forest(Xinjiashan forest).2. The soil microbial biomass carbon(MBC), dissolved organic carbon(DOC), and easily oxidizable carbon(EOC) decreased with the increase of soil depth on different forest soil profiles.The DOC contents of different depth on soil profiles of Picea asperata Mast forest and pine-oak mixed forest were all higher than other studied forest soils, the order of the mean DOC on different soil profiles were Picea asperata Mast forest>pine-oak mixed forest>Quercus aliena var acuteserrata forest(Ma Toutan forest)>Pinus tabulaeformis Carr forest> Pinus armandii Franch forest > Quercus aliena var. acuteserrata forest(Xin Jiashan forest).The contents of MBC of different forest soil profiles were 71.25 mg?kg-1 and 710.01 mg?kg-1, with a content sequence of Quercus aliena var acuteserrata forest(Ma Toutan forest)>Picea asperata Mast forest>pine-oak mixed forest>Pinus armandii Franch forest>Pinus tabulaeformis Carr forest>Quercus aliena var. acuteserrata forest(Xin Jiashan forest). The content of EOC on the whole soil profile of pine-oak mixed forest had a largest decline, and the order of the mean EOC were in the order pine-oak mixed forest>Picea asperata Mast forest>Quercus aliena var acuteserrata forest(Ma Toutan forest)>Pinus tabulaeformis Carr forest>Pinus armandii Franch forest>Quercus aliena var. acuteserrata forest(Xin Jiashan forest).3. The ratio of DOC content to SOC content of 0-60 cm soil layer of the six soils were in the order Pinus tabulaeformis Carr forest≧Quercus aliena var acuteserrata forest(Ma Toutan forest) > Pinus armandii Franch forest > pine-oak mixed forest > Quercus aliena var. acuteserrata forest(Xin Jiashan forest)>Picea asperata Mast forest. The ratio of MBC content to SOC content of 0-60 cm soil layer of the six soils were in the order Pinus tabulaeformis Carr forest>Quercus aliena var acuteserrata forest(Ma Toutan forest)>Pinus armandii Franch forest>pine-oak mixed forest>Quercus aliena var. acuteserrata forest(Xin Jiashan forest)>Picea asperata Mast forest. The ratio of EOC content to SOC content decreased with increasing soil depth on all of the six soil profiles. The ratio of MBC content to SOC content of 0-60 cm soil layer of the six soils were in the order Quercus aliena var acuteserrata forest(Ma Toutan forest)>pine-oak mixed forest>Pinus tabulaeformis Carr forest>Picea asperata Mast forest > Pinus armandii Franch forest > Quercus aliena var. acuteserrata forest(Xin Jiashan forest).4. SOC storage of 0-60 cm soil layer of the six soils were 150.94 t·hm-2 for Picea asperata Mast forest>135.28 t·hm-2 for Quercus aliena var acuteserrata forest(Matoutan forest)>124.93 t·hm-2 for pine-oak mixed forest>109.24 t·hm-2 for Pinus armandii Franch forest>102.15 t·hm-2 for Quercus aliena var acuteserrata forest(Xinjiashan forest)>96.62 t·hm-2 for Pinus tabulaeformis Carr forest, which was greater than the national average soil carbon storage(96.0 t·hm-2).5. Correlations analysis showed that there were highly significant positive correlations between SOC and TN, but no significant correlations between C/N and SOC and TN. The MBC, DOC and EOC contents of the different forest soils were significantly correlated to each other. There was significantly positive correlation among soil active carbon and TOC, TN. Meanwhile, there was no significantly correlation between soil active carbon and other soil basic physicochemical properties.