Carbon sequestration effect and influential factors in pedogenic carbonates of saline-alkaline soils from shore of rump salt lake in Xinjiang

China has a large area of arid and semi-arid zone. The soil carbonate is the main form of soil carbon pool in arid and semi-arid regions, which has an important scientific research value. Soil carbonate contains weathering information during soil formation, and the capacity of carbon sequestration of pedogenic carbonates is closely related to the base cations supplying, silicate minerals comprising and organic matters in the soils. In this study, to keep away the agricultural areas and the entering water system, we set 3 different typical sample plots (N、W、E) in the north ,west, and east shore of the rump salt Lake Abi. Respecting to the physical and chemical properties of soil and the characteristics of carbon isotopic fractionation of pedogenic carbonates, the carbon sequestration effect and influential factors in pedogenic carbonates of saline-alkaline soils from the shore of the Abi Lake had been investigated. The research results showed that there was a long-term and stable supply of Ca2+、Mg2+、Fe2+ and other cations derived from the weathering of silicate minerals during the process of saline-alkaline soils' formation in this study region. These cations of non-lithogenic carbonate sources came from the highlands around the lake basin carried into the low-lying catchment area in continuously by the water, wind and other forces etc., providing sufficient materials for soil carbonate to sequestrate modern atmospheric CO2. The average carbon density of soil carbonate carbon(SCC) was 4.05 times as many as that in soil organic carbon(SOC) in the saline-alkaline soils from shore of the Abi Lake. The results of δ13CSCC had indicated that the value ranged from -7.9‰ to 0.3‰, and there was a very significant negative correlation between δ13CSCC and HCO3- , and the correlation value (R2) is 0.669 9. One of the critical segment of secondary carbonate precipitation was that atmospheric carbon dioxide was dissolved into soil water in the form of bicarbonate ion. However, the δ13CSCC was also very significantly negatively correlated with the soil silicate minerals (actinolite, clinochlore and lllite). And with the increase of those Ca, Mg and Fe rich minerals in the soil, δ13CSCC decreased. Similarly, with more SOC content and higher biological weathering intensity in the soil, the δ13CSCC increased to bigger negative values. And in these cases, the pedogenic carbonate would sequestrate more light carbon from atmosphere. Ca2+ and Mg2+ contents of water-soluble salts and total salt with soil carbonate contents correlation value were not too high, but they were significantly correlated with the δ13CSCC in a concordant logarithmic relationship. The value was 0.758 7 and 0.694 7 respectively. If the biological weathering process was restrained by extremely higher soil salinity, the results implied that the pedogenic carbonate would sequestrate more heavy carbon. In this research, the transfer of carbon dioxide to bicarbonate-carbonate was mainly an inorganic process, when the salt content was more than 20 g/kg, and the δ13CSCC basically value was greater than -2. However, there was a coupling effect between organic process and inorganic process in carbon sequestrating. If the vegetation coverage was considered, the SOC pool could be increased. And in this way, the silicate weathering in soil could be strengthened by high concentration CO2 that was fractionated from biological process, and instead of returning to atmosphere. Hence, the pedogenic carbonate in arid areas has great potential capacity for atmospheric CO2 sequestration.