[Spatial Characterization of Stable Isotope Composition of Organic Carbon from Farmland Soils in Chongqing].

Soil was sampled from 182 profiles in typical farmlands of Chongqing and analyzed for the stable carbon isotope composition of organic matter (δ13CSOC). The results showed that the values of δ13CSOC for each soil profile were gradually increasing with increasing soil depth, and the mean values were (-23.63±1.53)‰, (-22.43±1.59)‰, and (-21.42±1.90)‰ for surface, middle, and bottom layers, respectively. The δ13CSOC values in the northeastern region of Chongqing tended to be more negative, whereas those in central Chongqing were less negative. Paddy fields showed the most negative values of δ13CSOC, followed by rice-upland rotating fields and upland fields, with the average being (-25.32±0.93)‰, (-23.17±1.37)‰, and (-24.75±1.28)‰ for the surface layers, respectively. For different soil types, the δ13C values in the surface layers were in the order of paddy soil