Sequestering carbon (C) into stable soil pools has potential to mitigate increasing atmospheric carbon dioxide concentrations. Carbon accrues in grassland soil restored from cultivation, but the amount of physically protected C (here measured as microaggregate-within-macroaggregate C) and predominant mechanisms of accrual are not well understood. We modeled the rate of physically protected carbon accrued in three mesic temperate perennial restored grasslands from cross-continental regions using datasets with a wide range of restoration ages from northeast Kansas, USA; southeast Nebraska, USA; and northeast Free State, South Africa. Further, we investigated major controls on the amount of physically protected C in each site using structural equation modeling. Variables in the structural equation model were root biomass, root C:N ratio, soil structure (indicated by bulk density, percent of macroaggregates on a per whole soil mass basis, and percent of microaggregate-within-macroaggregates on a per macroaggregate mass basis), microbial composition (indicated by microbial biomass C, total phospholipid fatty acid [PLFA] biomass, and PLFA biomass of arbuscular mycorrhizae fungi [AMF] biomass), and microaggregate-within-macroaggregate C on a per whole soil mass basis. Across all sites, physically protected C accrued at a rate of 16 ± 5 g m⁻² year⁻¹. Data from South Africa fit an a priori metamodel developed for northeast KS that hypothesized physically protected C could be explained as a function of microbial composition, soil structure, root C:N ratio, and root biomass (listed in order of strength of direct effect on physically protected C). In contrast to the model-based hypothesis, root C:N ratio was the strongest influence (negative) on physically protected C in South Africa. The lesser effect of AMF on physically protected C in South Africa was consistent with lower AMF biomass in arid environments. The hypothesized model did not fit southeast Nebraska data possibly due to high (~ 30%) clay content. Overall, these results suggest that physically protected C in soil with moderate amounts of clay (more than 10% and less than 30%) can be predicted with knowledge of roots (biomass and C:N ratio), microbial biomass, and soil aggregation.

将碳（C）隔离到稳定的土壤池中具有缓解大气中二氧化碳浓度增加的潜力。从耕作中恢复后的草地土壤中积碳，但是对物理保护的C的量（此处为微骨料中的宏观骨料C的量）和主要的累积机理尚不十分了解。我们使用来自美国东北堪萨斯州的不同恢复年龄的数据集，对跨大陆地区的三个中温温带多年生恢复草地的物理保护碳积累速率进行了建模。美国内布拉斯加州东南部；和东北自由州，南非。此外，我们使用结构方程模型研究了每个站点中受物理保护的C量的主要控制措施。结构方程模型中的变量是根生物量，根C：N比，土壤结构（以堆积密度表示，以整个土壤质量为基准的大颗粒集料的百分比，以每个大集合质量为基础的微集料中的宏观集料的百分比），微生物组成（以微生物生物量C表示，总磷脂脂肪酸[PLFA]表示）的生物量和丛枝菌根真菌的PLFA生物量[AMF]生物量，以及基于整个土壤质量的微团聚体-宏观团聚体C。在所有站点中，以16±5 gm的速率累积了受物理保护的C 以及基于整个土壤质量的微团聚体中的宏观团聚体C。在所有站点中，以16±5 gm的速率累积了受物理保护的C 以及基于整个土壤质量的微团聚体中的宏观团聚体C。在所有站点中，以16±5 gm的速率累积了受物理保护的C^－2年^－1。南非的数据具有先验性为堪萨斯州东北部开发的元模型，假设了物理保护的碳可以解释为微生物组成，土壤结构，根碳氮比和根生物量的函数（按对物理保护的碳的直接作用强度顺序列出）。与基于模型的假设相反，根部碳氮比对南非受物理保护的碳影响最大（负）。在南非，AMF对受物理保护的碳的较小影响与干旱环境中较低的AMF生物量一致。假设的模型可能与内布拉斯加州东南部的数据不符，这可能是由于粘土含量较高（约30％）所致。总体而言，这些结果表明，通过了解根系（生物量和碳氮比），微生物生物量，