A warming climate will cause shrubification and less winter snow cover in peatlands, which are an important global carbon sink. Both shrubification and snowpack reduction affect organic carbon sequestration, yet their effects on the dynamics of microbial necromass carbon (MNC) and plant necromass carbon (PNC) in rhizosphere soil are indeterminate. This investigation focuses on the effects of shrubification and snow cover changes on organic carbon components and their mechanisms in rhizosphere soil. For this purpose, a field in situ experiment on snow cover removal and natural snow cover was conducted in shrub and herb peatlands, respectively, in winter, and rhizosphere soil samples were collected in the following growing season. The MNC biomarker amino sugar and the PNC biomarker lignin phenol were quantified, and in addition to the general soil physical, chemical, and biological parameters, root exudates were measured based on untargeted metabolomics. The findings showed that MNC contributes more to SOC in spring, with the majority of it derived from fungal necromass carbon, and the contribution of PNC to SOC gradually increased in later seasons, with a consequent decrease in rhizosphere SOC stability. Shrubification decreased the MNC content by 15.80% and the PNC content by 7.68%, whereas snow removal increased the MNC content by 8.24% and 2.58% and the PNC content by 11.31% and 17.39% in shrub and herb peatlands, respectively. The changes in root exudates may be an important factor regulating the accumulation of different SOC components. Specifically, sugars and amino acids had a positive priming effect on MNC and PNC, whereas organic acids had a negative priming effect. The mechanisms by which root exudates mediated MNC and PNC accumulation differed depending on the season. This research will be useful in forecasting future changes in carbon sink function and providing a theoretical foundation for increasing carbon sink measures.