To investigate the mechanisms of the effects of different frequencies and intensities of freeze-thaw cycles on the soil carbon mineralization process and the characteristics of stable carbon isotope （δ¹³C） fractionation in alpine swamp meadows， this study focused on the soil of alpine swamp meadows on the Qinghai-Tibet Plateau. Two freeze-thaw intensities （-15 to 15℃ and -10 to 10℃， a total of 15 freeze-thaw cycles） and a control group at 10℃ were established. A 15-day indoor continuous monitoring experiment was conducted to compare the dynamics of carbon mineralization and changes in δ¹³C. The results showed that low-intensity freeze-thaw cycles significantly inhibited the rate of carbon mineralization， causing a decrease of 7.67%. In contrast， high-intensity freeze-thaw cycles significantly promote the cumulative carbon mineralization， with an increase of 2.70%. The differences among treatments were relatively small after the first 3 freeze-thaw cycles， but the growth rate of carbon mineralization significantly slowed down under the low-intensity treatment after the third cycle. The δ¹³C values under different freeze-thaw intensities ranged from -21.49‰ to -28.03‰， which showed -15-15℃>10℃>-10-10℃， and showed a trend of first decreasing and then increasing with the increase of freeze-thaw frequency. Redundancy analysis （RDA） showed that ammonium nitrogen （NH₄⁺-N） and microbial biomass nitrogen （MBN） were the key factors regulating carbon mineralization and isotope fractionation. Under the -15-15℃ treatment， δ¹³C values were significantly positively correlated with nitrate nitrogen （NO₃^--N）. In contrast， under the -10-10℃ treatment， the carbon mineralization rate was significantly negatively correlated with MBN and significantly positively correlated with microbial biomass carbon to microbial biomass nitrogen ratio （MBC/MBN）. Additionally， its stable isotopes were significantly positively correlated with NH₄⁺-N and MBC/MBN. Overall， the reduced freeze-thaw intensity significantly inhibits soil carbon mineralization processes and causes changes in microbial metabolic pathways. It is crucial to pay attention to the long-term impacts of the continued weakening in freeze-thaw intensity on the carbon sequestration function of alpine wetlands.

Soil carbon mineralization  /  Stable isotopes  /  Freeze-thaw cycle  /  Alpine swamp meadows  /  Qinghai Lake