Vertical Distribution of Soil organic Carbon and its Influencing Factors Under Different Land use Types in the Desert Riparian Zone of Downstream Heihe River Basin, China

The amount of soil organic carbon (SOC) reflects the ability of ecosystem to sequester carbon (C). In the desert riparian zone of Heihe River basin, northwest China, that has been the subject of an ecological water conveyance since 2000, studies on SOC under different land use types remain scarce. Yet analyzing soil organic carbon content (SOCC) and its spatial distribution in the area is a key component when studying C cycle in this desert ecosystem. We therefore investigated the vertical distribution of SOC and its influencing factors using field study, and we found significant differences among different land use types and soil depths. The average SOCC and soil organic carbon density in the 0-100 cm soil layers were 23.31 g kg(-1) and 6.08 kg m(-2), respectively. SOCC and soil organic carbon density decreased in the following order: grassland (5.73 g kg(-1)) > forestland (5.03 g kg(-1)) > shrubland (4.79 g kg(-1)) > cropland (4.28 g kg(-1)) > Gobi desert (2.10 g kg(-1)). We also found that vegetation and soil properties jointly affected SOCC in this riparian arid zone, in addition to human disturbance, as indicated by a low stratification ratio in the grassland (1.575) and cropland (1.366). When natural vegetation was transformed into cropland, SOCC decreased with the removal of plant biomass and the increase of wind erosion. Consequently, conservation agricultural practices that consider preservation of soil organic matter (e.g., no-tillage and intercropping with deep-rooted leguminous perennial plants) should be introduced in order to prevent further degradation.