Contribution of Root Biomass to Soil Organic Carbon Under Complex Landforms Conditions

: Quantifying the contribution of fine root density (FRD) to soil organic carbon density (SOCD) under extremely complex landforms is of great significance for the evaluation of carbon storage at an eroded small catchment in hilly regions of the Loess Plateau. Soil and root samples were collected from typical landforms (a ridge slope, gully slope, and valley bottom) and different vegetation types (cropland, grassland, and woodland) to investigate the contribution of FRD to SOCD at the Zhuan Yaogou watershed The spatial distribution of SOCD and FRD was influenced significantly by landforms, vegetation type, soil depth, or their interactions. SOCD and FRD tended to go in the following order:valley bottom > gully slope > ridge slope on different landforms,Woodland > grassland > cropland on different types of vegetation, and surface > lower depths at different soil depths. Additionally, FRD had a significant effect on SOCD (P<0.05), SOCD increased logarithmically with FRD, and there was a significant difference in root-carbon conversion efficiency between different landforms and types of vegetation (P<0.05). The root-carbon conversion efficiency on the valley bottom (0.87) was 2.0 times higher than those on ridge slopes (0.43) and gully slopes (0.43) on cropland; the root-carbon conversion efficiency on gully slopes (0.57) were 1.3 and 2.1 times greater than those in valley bottoms (0.45) and ridge slopes (0.27), respectively, on grassland; and the root-carbon conversion efficiency on ridge slopes (0.56) was 1.3 times greater than that on gully slopes (0.44). Therefore, from the perspective of increasing root-carbon conversion efficiency at the Zhuan Yaogou watershed in the hilly region of the Loess Plateau, valley bottoms are suitable for agriculture, gully slopes are suitable for returning farmland to grassland, and ridge slopes are suitable for returning farmland to woodland.