Distribution patterns of organic carbon and its isotope compositions in soil profiles on the slopes in Puding karst areas of Guizhou Province, Southwest China

Soil samples were collected from two types of slope soil profiles with different lithology(clastic rock and carbonate rock) around the Puding County of Guizhou Province,and their pH values,C/N ratios,organic carbon(SOC) contents,and SOC isotope compositions were analyzed,aimed to approach the distribution patterns of SOC and δ13CSOC in the two types of the soil profiles at different slope positions.The results showed that the SOC contents in the profiles of sandstone yellow soil and limestone yellow soil ranged from 3.1-79.7 g·kg-1and 8.2-73.3 g·kg-1,respectively.From the top to the bottom of the slopes,the SOC contents in the two soils showed the same distribution pattern,i.e.,slope bottom slope top slope waist.Across each soil profile,the SOC content decreased as a function of soil depth,except that of the sandstone yellow soil profile on the slope top.The δ13CSOC values in the profiles of sandstone yellow soil and limestone yellow soil varied in the range of-25.4‰ to-20.7‰ and-23.2‰ to-18.8‰,respectively.Except for the limestone yellow soil profile on the slope waist,the δ13CSOC values in the other soil profiles increased firstly from the surface layer to the 20-40 cm depth,then decreased as a function of soil depth,and finally kept stable at the base of the soil profiles.The variations of the SOC contents and the δ13CSOC values as a function of soil depth could be due to the input of plant residue and its degradation and accumulation in soil.This study provided insights to the slope soil erosion and the effects of pedogenic process on the SOC circulation of slope soils.