Contribution of hydrological connectivity to the retention of soil organic carbon by vegetation patches: Insight from a dryland hillslope on the Loess Plateau, China

Abstract

Hydrological connectivity affects the carbon capture and redistribution over landscapes. However, the contribution of hydrological connectivity to the spatial heterogeneity of carbon sequestration, particularly the spatial variation of carbon retention, is not well covered in carbon inventory and estimation. This study addressed the contribution of hydrological connectivity to the soil carbon retention on a hillslope with a mosaic of shrub patches and inter-shrub area covered by grass, biological crust and bare soil on the Loess Plateau, China. The variation of the efficiency of the shrub patches to retain SOC and the SOC difference between shrub patch and inter-shrub area among slope positions were revealed in the context of varied hydrological connectivity indicated by the contributing area. The results illustrate that the efficiency of shrub patches to retain sediment and SOC transported from upslope areas decreased from the hillslope top to the slope foot, though the morphological traits of the shrub patches did not significantly varied. The mean SOC in shrub patches declined, and increased in inter-shrub areas from hillslope top to slope foot. Consequently, the SOC difference between shrub patch and inter-shrub area declined from the top to the foot of the hillslope. These results imply that the size of contributing areas is the dominant contributor to the spatial variation of the efficiency of shrub patches to retain SOC, and the pattern of SOC difference between shrub patches and inter-shrub areas. The results highlight the necessity to incorporate the spatial heterogeneity of hydrological connectivity into evaluating the carbon retention efficiency of vegetation, especially in the dryland landscape. This study also revealed that the lack of hydrological connectivity may lead to great uncertainty in assessing SOC sequestration in terrestrial landscapes.