Objective Conducting research on the impact of freeze-thaw conditions on soil active organic carbon can provide basic data and theoretical basis for the study of organic carbon conservation and carbon balance in black soil areas.

Method Taking typical middle layer black soil in Dehui area as the research object, the effects of different freeze-thaw cycles, freezing time, freeze-thaw temperature, and moisture content on soil active organic carbon were investigated through freeze-thaw control experiments.

Result There were significant differences in the response of soil active organic carbon components to freeze-thaw conditions. The content of Dissolved Organic Carbon (DOC), Light Organic Carbon (LFOC), and Particulate Organic Carbon (POC) in soil gradually increases with the increase of freeze-thaw cycles, and the growth rate slows down after 20 freeze-thaw cycles; Soil Microbial Biomass Carbon (MBC) fluctuates between 0.160 g kg⁻¹ and 0.164 g kg⁻¹ after 12 freeze-thaw cycles. Both a decrease in freezing temperature and an increase in melting temperature can promote an increase in soil DOC, LFOC, and POC content, while the soil MBC content decreases with a decrease in freezing temperature and increases with an increase in melting temperature. However, the content still decreases by 10.42% to 24.48% compared to the control state. The content of soil DOC, LFOC, and POC showed significant differences with the increase of freezing time, with a significant increase from 12 to 48 hours; The increase in freezing time resulted in a significant decrease in soil MBC content, with a decrease of 52.60% at 96 hours of freezing time. As the moisture content increases, the content of soil DOC, LFOC, and POC gradually increases. When the relative moisture content is between 80% and 100%, the increase in LFOC content is most significant, ranging from 9.69% to 38.48%; The soil MBC content gradually decreases, and the decrease tends to be gradual when the relative water content is between 80% and 100%.

Conclusion The freeze-thaw cycle is beneficial for enhancing or maintaining soil organic carbon, and frequent freeze-thaw cycles can increase the content of some active organic carbon components and promote soil nutrient cycling.