Objective To investigate the impact of fire disturbance on the soil micro-ecological environment in temperate grassland, elucidate the variation patterns of key soil carbon cycle indicators post-fire, and provide a scientific basis for ecosystem restoration and sustainable carbon stock management following grassland fires.

Method This study focused on grasslands in FuYu County, Heilongjiang Province, specifically selecting fire-affected sites 1 year (F1), 3 years (F3), and 5 years (F5) after the fire, with an unburned area serving as the control (CK). We measured soil physicochemical properties((pH,moisture content,temperature,available phosphorus, available potassium), organic carbon components (dissolved organic carbon DOC, particulate organic carbon POC, readily oxidizable organic carbon, ROC), microbial biomass (microbial biomass carbon, MBC; microbial biomass nitrogen, MBN), and humic substance content were measured.We then conducted a comparative analysis to assess the impact of fire disturbance on key indicators of the soil micro-ecosystem and carbon cycle.

Result (1) Fire disturbance significantly altered soil physical and chemical properties, resulting in decreased soil pH, increased moisture and temperature, and a notable elevation in available nutrients, particularly potassium. (2) Compared with unburned plots, fire disturbance also exerted a significant influence on soil organic carbon fractions, demonstrating a differential response pattern characterized by an initial decrease (F1, F3) followed by an increase (F5) in active components (DOC), a continuous decline in particulate organic carbon (POC), and a relatively stable trend in readily oxidizable carbon (ROC). (3) Microbial biomass carbon (MBC) and nitrogen (MBN) both exhibited a trend of initial increase followed by a decrease with recovery years. After five years of fire suppression, MBC and MBN levels approached those of unburned areas, indicating that the soil microbial biomass carbon and nitrogen pools had largely recovered to pre-fire conditions, reflecting the robust self-restoration capacity of soil microbial communities in cold-temperate grasslands. (4) Total humus, humic acid, and fulvic acid content displayed a fluctuating trend of “crease (F1)—decrease (F3)—increase (F5)”with recovery years, while humin content showed no significant change. This suggests that fire disturbance primarily affected the more labile, soluble components of humus, with comparatively limited perturbation to the stable organic carbon pool.

Conclusion Five years post-fire, soil labile nutrient pools significantly increased, soluble carbon stocks recovered and surpassed unburned levels, and total humus content notably rose. These findings indicate that fire disturbance positively enhances soil carbon sequestration function on a long-term scale and drives the soil microbial ecological environment through a temporal succession of “short-term perturbation—mid-term adjustment—long-term recovery”. This research elucidates the dynamic transformation mechanisms of soil carbon pools in burned areas of temperate grasslands, providing critical parameters and scientific evidence for grassland ecological restoration, carbon stock assessment, and fire prevention and management.