Increasing carbon input (CI) to soil has been widely recommended (e.g., residue retention and manure application) to sequester more carbon in agricultural soils thereby mitigating climate change and improving soil quality. However, carbon sequestration may not respond linearly to additional CI due to their active interactions with the turnover of native soil organic carbon (SOC) via such as the priming effect and mediating SOC accessibility to decomposition. In this study, we collected SOC measurements from 22 long-term paired trials (12–142 years) with two levels of CI [i.e., a treatment with carbon input (+CI) and another treatment with less carbon input (-CI) compared with + CI] across the globe. We used these observed SOC to constrain a carbon model and analyse SOC turnover processes as impacted by CI to the soil. The results show that there are divergent responses of SOC turnover processes to CI, indicated by large variability of changes in decay rates of carbon pools, transfer coefficient of carbon flow from fast to slow pools, and physical accessibility to decomposition. Initial SOC at the start of the trial, the average amount of CI during the experiment, and soil bulk density are the three most important variables underlying such divergent responses. Simulation experiments suggest that these discrepancies in SOC turnover processes induced by CI have significant consequences on the efficiency of increasing carbon inputs for SOC sequestration. Ignoring the effect of additional CI leads to overestimation or underestimation of CI required to achieve typical SOC sequestration targets depending on baseline SOC content and temperature. Our results demonstrate the vital role of CI in regulating SOC turnover processes, which have site-specific consequences on the management of carbon inputs to sequester SOC.

增加土壤的碳输入 (CI) 已被广泛推荐（例如，残留物保留和施肥）以在农业土壤中封存更多的碳，从而缓解气候变化并改善土壤质量。然而，碳固存可能不会对额外的 CI 做出线性响应，因为它们与原生土壤有机碳 (SOC) 的周转有积极的相互作用，例如启动效应和介导 SOC 对分解的可及性。在这项研究中，我们从 22 项长期配对试验（12-142 年）中收集了 SOC 测量值，这些试验具有两个水平的 CI [即，一种碳输入 (+CI) 处理和另一种碳输入较少 (-CI) 的处理比较与 + CI] 遍布全球。我们使用这些观察到的 SOC 来约束碳模型并分析受 CI 对土壤影响的 SOC 周转过程。结果表明，SOC 周转过程对 CI 有不同的响应，表现为碳池衰减率、碳从快到慢池的转移系数以及分解的物理可及性的变化很大。试验开始时的初始 SOC、试验期间的平均 CI 量和土壤容重是造成这种不同反应的三个最重要的变量。模拟实验表明，由 CI 引起的 SOC 周转过程中的这些差异对增加用于 SOC 封存的碳输入的效率具有显着影响。忽略额外 CI 的影响会导致高估或低估实现典型 SOC 封存目标所需的 CI，具体取决于基线 SOC 含量和温度。