The ¹³C and ¹⁵N Natural Abundances to Characterize Soil Organic Matter Associated with Clay Minerals in Eurasian Steppe Soils (THE 2nd INTERNATIONAL CONFERENCE ON ARID LAND (ICAL 2)) The ¹³C and ¹⁵N Natural Abundances to Characterize Soil Organic Matter Associated with Clay Minerals in Eurasian Steppe Soils

Soil organic matter (SOM) associated with clay minerals plays an important role in maintaining fertility and storing carbon in soil. Moreover, for soil conservation, it is necessary to understand the nature of SOM associated with clay minerals in various environments. Our objective was to characterize SOM associated with clay minerals in Eurasian steppe soils using particle size fractionation and stable isotopic techniques. In this study, we collected 43 samples from grassland soils in Ukraine, Kazakhstan, and Mongolia as well as Xinjiang and Inner Mongolia in China, and conducted particle size fractionation to evaluate SOM associated clay minerals. The results revealed that SOM associated with clay minerals plays a key role in the fertility of Eurasian steppe soils (52.5% ± 9.0% C and 55.0% ± 8.2% N in total organic carbon and total nitrogen). The C/N ratio decreased in the following order: sand (13.5 ± 5.5) > silt (11.5 ± 2.0) > clay (8.6 ± 1.0). The δ¹³C and δ¹⁵N values of clay fractions were higher than those of silt and sand fractions in most samples. The C/N, δ¹³C, and δ¹⁵N values suggested that SOM associated with clay minerals contains more decomposed SOM. In addition, the difference of δ¹⁵N values between clay and silt fractions had a larger range than that of δ¹³C values. This indicated that δ¹⁵N values of SOM were a useful tool for clearly showing the difference of quality between particle size fractions in Eurasian steppe soils.