Grasslands store large amounts of C; however, the underlying mechanisms of soil C sequestration after grazing exclusion are not well known. This study aimed to elucidate the drivers of soil organic C (SOC) sequestration from plant and microbial residues in temperate grasslands after long-term (~ 40 years) grazing exclusion. We conducted in situ ¹³C-CO₂ labelling experiments in the field and traced ¹³C in plant-soil systems paired with biomarkers to assess the C input from plants into soils. Long-term grazing exclusion increased all plant and soil pools including shoots, roots, microbial biomass and necromass. ¹³C allocation in these pools also increased, whereas ¹³C was lost via respiration as CO₂ from soils decreased. ¹³C incorporation into the soil and microbial biomass increased with ¹³C allocation into the roots. Grazing exclusion for over 40 years increased the total SOC content by 190%, largely due to increases in fungal necromass C, and there was a minor contribution of lignin phenols to SOC accrual (0.8%). Consequently, grazing exclusion boosts not only aboveground biomass, but also larger roots and rhizodeposition, leading to microbial biomass and necromass formation. Microbial necromass and lignin phenols contribute to SOC accrual under grazing exclusion, and microbial necromass, especially fungal necromass, makes a larger contribution than lignin phenols.

草原储存大量的碳；然而，禁牧后土壤固碳的潜在机制尚不清楚。本研究旨在阐明长期（约 40 年）禁牧后温带草原植物和微生物残留物固存土壤有机碳 (SOC) 的驱动因素。我们在田间进行了原位¹³ C-CO ₂标记实验，并在植物-土壤系统中追踪了¹³ C，并与生物标记物配对，以评估从植物到土壤的 C 输入。长期放牧排除增加了所有植物和土壤池，包括芽、根、微生物生物量和坏死物。这些池中的¹³ C 分配也增加了，而随着土壤中CO _{2 的减少，} ¹³ C 通过呼吸作用损失了。随着¹³ C 分配到根部，¹³ C融入土壤和微生物生物量增加。 40 多年的禁牧使总 SOC 含量增加了 190%，这主要是由于真菌坏死物 C 的增加，木质素酚对 SOC 的增长贡献较小（0.8%）。因此，放牧排斥不仅增加了地上生物量，而且增加了更大的根和根际沉积，导致微生物生物量和坏死物的形成。微生物坏死物和木质素酚对禁牧条件下 SOC 的增加有贡献，并且微生物坏死物，特别是真菌坏死物，比木质素酚做出更大的贡献。