Soil carbon fractions of restored lands in Liusha River Valley, Sichuan

Restored engineering leads to the sequestration of soil organic carbon (SOC), including labile and refractory fractions in the soils of the degraded lands. This study was conducted to estimate the changes in SOC fractions in the topsoil of croplands, horticultural plots and afforestation areas from degraded lands in the Liusha River Valley, Sichuan. The cover and shoot biomass of plants, soil thickness and bulk density in the restored lands differed significantly from those of the degraded lands (P < 0.05). When compared with the degraded lands, the concentrations of SOC fractions in restored lands were substantially enhanced (P < 0.05). Among the three restoration classes, the concentrations of total organic carbon (TOC), dichromate oxidizable carbon, permanganate oxidizable carbon (POXC) and water-soluble carbon (WSOC) were higher in the croplands and afforestation areas than in the horticultural plots (P < 0.05), while the humic carbon and humic acid carbon (HAC) were higher in the afforestation areas than in the horticultural plots (P < 0.05). The SOC fraction concentrations displayed significant relationships with the cover and shoot biomass of plants, elevation, soil thickness and bulk density (P < 0.05), except that WSOC showed no relationship with elevation (P > 0.05). Additionally, POXC, WSOC and HAC represented 14.62–16.17, 0.91–1.15 and 7.73–8.66% of the TOC of the restored soils, respectively, and improved significantly during the restoration process. Therefore, these fractions can be considered indicators of changes in restoration-induced soil quality and sensitivity to environmental factors and restoration practices.