Plant carbon (C) inputs via shoot, roots, and the associated mycorrhizal fungi are vital drivers of soil organic C (SOC) stock and turnover. Both the amounts and proportions of plant C inputs to the soil through these pathways can be affected by soil fertility. Yet, we know little about how divergent pathways of plant C inputs contribute to SOC cycling under different soil fertility. By growing the C4 grass Cleistogenes squarrosa in C3 soils, we quantified the contributions of shoot, roots, and arbuscular mycorrhizal fungi (AMF) to SOC turnover with different fertility in a temperate grassland. Our four-year field experiment showed that soils with higher fertility sequestered more shoot-, root- and AMF-derived C, which were mainly driven by greater soil microbial biomass. Irrespective of soil fertility, roots contributed the most (44%) to new SOC formation, while shoot (28%) and AMF (28%) exerted similar but lower contributions. We found that the positive priming effects induced by roots and AMF were greater in more fertile soils, which were primarily associated with more root- and AMF-derived C, respectively. Across all the soil fertility levels, root pathway had an equal impact on new SOC accumulation and native SOC losses via priming effects, and thus caused no net SOC changes. However, the priming effect induced by AMF pathway was 60% higher than the root pathway across treatments. The disproportionately large priming effects relative to new SOC accumulation induced by AMF led to net SOC losses, especially in soils with higher fertility. Overall, we demonstrated that plant C inputs through shoot, root, and mycorrhizal pathways have differential impacts on SOC turnover. Our quantitative estimation should be valuable for more accurately modeling how much plant-derived C can be sequestered in the soils and advancing our understanding of future SOC dynamics under global changes.

通过芽、根和相关菌根真菌输入的植物碳 (C) 是土壤有机碳 (SOC) 储量和周转的重要驱动因素。通过这些途径向土壤中输入植物碳的数量和比例都会受到土壤肥力的影响。然而，我们对不同土壤肥力下植物 C 输入的不同途径如何促进 SOC 循环知之甚少。通过种植 C4 草Cleistogenes squarrosa在 C3 土壤中，我们量化了地上部、根部和丛枝菌根真菌 (AMF) 对温带草地不同肥力的 SOC 周转的贡献。我们为期四年的田间试验表明，肥力较高的土壤固存了更多地上部、根部和 AMF 衍生的碳，这主要是由更大的土壤微生物生物量驱动的。无论土壤肥力如何，根系对新 SOC 形成的贡献最大 (44%)，而地上部 (28%) 和 AMF (28%) 的贡献相似但较低。我们发现，在更肥沃的土壤中，根和 AMF 诱导的正启动效应更大，这主要分别与更多的根和 AMF 衍生的 C 相关。在所有土壤肥力水平上，根途径通过启动效应对新的 SOC 积累和原生 SOC 损失具有相同的影响，因此没有造成净 SOC 变化。然而，AMF 通路诱导的启动效应比根通路高 60%。相对于 AMF 诱导的新 SOC 积累而言，不成比例的大启动效应导致净 SOC 损失，尤其是在肥力较高的土壤中。总体而言，我们证明植物 C 通过芽、根和菌根途径输入对 SOC 周转有不同的影响。我们的定量估计对于更准确地模拟土壤中可以隔离多少植物来源的 C 并促进我们对全球变化下未来 SOC 动态的理解应该是有价值的。相对于 AMF 诱导的新 SOC 积累而言，不成比例的大启动效应导致净 SOC 损失，尤其是在肥力较高的土壤中。总体而言，我们证明植物 C 通过芽、根和菌根途径输入对 SOC 周转有不同的影响。我们的定量估计对于更准确地模拟土壤中可以隔离多少植物来源的 C 并促进我们对全球变化下未来 SOC 动态的理解应该是有价值的。相对于 AMF 诱导的新 SOC 积累而言，不成比例的大启动效应导致净 SOC 损失，尤其是在肥力较高的土壤中。总体而言，我们证明植物 C 通过芽、根和菌根途径输入对 SOC 周转有不同的影响。我们的定量估计对于更准确地模拟土壤中可以隔离多少植物来源的 C 并促进我们对全球变化下未来 SOC 动态的理解应该是有价值的。