Effects of Freeze–Thaw Cycles on Soil Properties and Carbon Distribution in Saline-alkaline Soil of Wetland

The effects of freeze-thaw cycles on the physicochemical properties and carbon components in saline-alkali wetland soil were investigated.The results showed that the water content and bulk density of the soil increased, while soil pH decreased with increasing number of freezethaw cycles.Organic carbon content in the soil was not significantly affected by the freezethaw cycles.In contrast, water-soluble organic carbon (WSOC), microbial biomass carbon (MBC), and readily oxidized organic carbon (ROOC) contents were significantly affected by the cycles.The various carbon contents showed a common tendency to increase first and then decrease steadily with repeated cycles; the change in carbon content was stable after several freeze-thaw cycles.The correlation between soil organic carbon and active carbon components was significant within the temperature range of -5-5 ℃.However, the correlation became significant only after the first cycle.Repeated cycles and low freeze-thaw temperatures seem to affect the redistribution of carbon components in the soil.The results of this study provide basic data to support the accurate estimation of the effects of freeze-thaw cycles on soil carbon pools in saline-alkali wetlands and to reveal the responses of soil physical and chemical properties and active carbon components to the cumulative effects of freeze-thaw cycles.