Abiotic carbonate dissolution traps carbon in a semiarid desert.

It is generally considered that desert ecosystems release CO2 to the atmosphere, but recent studies in drylands have shown that the soil can absorb CO2 abiotically. However, the mechanisms and exact location of abiotic carbon absorption remain unclear. Here, we used soil sterilization, (13)CO2 addition, and detection methods to trace (13)C in the soil of the Mu Us Desert, northern China. After (13)CO2 addition, a large amount of (13)CO2 was absorbed by the sterilised soil, and (13)C was found enriched both in the soil gaseous phase and dissolved inorganic carbon (DIC). Further analysis indicated that about 79.45% of the total (13)C absorbed by the soil was trapped in DIC, while the amount of (13)C in the soil gaseous phase accounted for only 0.22% of the total absorbed (13)C. However, about 20.33% of the total absorbed (13)C remained undetected. Our results suggest that carbonate dissolution might occur predominately, and the soil liquid phase might trap the majority of abiotically absorbed carbon. It is possible that the trapped carbon in the soil liquid phase leaches into the groundwater; however, further studies are required to support this hypothesis.