Δ14C variations of pedogenic carbonate in Mongolian steppe soils under a vegetation sequence

Abstract

To provide information on the dynamics of inorganic carbon in the soil environment, vertical distributions of the Δ14C values of pedogenic carbonate were measured in Mongolian steppe soils under a vegetation sequence. Soil samples were taken from five sites in a forest steppe, steppe and govi steppe. Δ14C values for pedogenic carbonate at all sites ranged from −392‰ to −776‰. There were remarkable differences in vertical distributions of inorganic carbon contents and Δ14C values between the forest and govi steppe sites. In the forest steppe and steppe sites where inorganic carbon was not present in the A horizons, the vertical distribution of Δ14C values varied widely with depth. On the other hand, soils in the govi steppe contained inorganic carbon throughout the whole soil profile, and the Δ14C value decreased regularly with depth. In addition, soil pH and organic carbon and total nitrogen contents showed differences among the vegetation zones. From comparison of results from samples of forest steppe and steppe sites to those from govi steppe sites, it was found that vegetation and the soil chemical environment have a great effect on Δ14C values.