Factors affecting soil organic carbon density for Betula albo-sinensis forests on the Southern Slope of the Qinling Mountains

Soil organic carbon,the main part of the terrestrial ecosystem carbon pool,is an essential component of the terrestrial carbon cycle,and one of the most important components of research on global change. Accurate estimation of soil organic carbon storage is important for determining the role that soil organic carbon plays in the terrestrial ecosystem carbon cycle,and thus in changes in the global environment. Forest soil organic carbon storage changes according to topography and forest conditions; therefore,research on forest organic carbon in a variety of such conditions is essential to determine the relationship between soil organic carbon storage,and factors related to topography and forest conditions. Betula albo-sinensis forest is one of the principal forest types in the Qinling Mountains. This study aimed to analyze the distribution patterns of soil organic carbon density( SOCD),and to reveal the relationship between soil organic carbon density and factors influencing Betula albo-sinensis forest on the southern slopes of the Qinling Mountains. We investigated topographical,stand,and soil factors of 122 plots,each of which was 20x30 m. Inventory data( i.e.,elevation,gradient,slope position,slope aspect,canopy density,plant cover,biomass,mean height,and mean diameter at breast height) of Betula albosinensis individuals in each plot were measured and recorded. Soil samples were tested for SOCD,moisture density,and bulk density. Results indicated that the average SOCD was( 69.02+ or -12.90) t / hm~2. In virgin forest,the average SOCD was( 76.21+ or -10.83) t /hm~2,in secondary forest,( 65.24+ or -12.32) t /hm~2. The difference in average SOCD between them was significant. The average SOCD decreased with soil depth increasing,and the average SOCD for soil layers A-C was( 31.52+ or -6.57),( 27. 18 + or - 6. 49),and( 10. 32 + or - 2. 65) t / hm~2,respectively. The average SOCD( t /hm~2) differed by forest region( Xunyangba=( 58.80 + or - 10.29),Huoditang =( 67. 95 + or - 10. 25),Huangbaiyuan =( 69.63 + or - 12. 78),and Guanyinshan =( 75.82+ or -12.30)). One-way ANOVA analysis showed that differences in average SOCD were significant for the four forest regions and soil layers,but not significant for slope positions. Differences in SOCD between shady and sunny slopes were insignificant,based on t-tests. Correlation analysis showed that SOCD was positively correlated with elevation,stand age,arbor biomass,and herb biomass,but negatively correlated with surface