The interaction of organic carbon (OC) with clay and metals stabilizes soil carbon (C), but the influence of specific clay-metal-OC assemblages (flocs) needs further evaluation. This study aimed to investigate the stability of flocs in soil as affected by external C inputs. Flocs representing OC-mineral soil fractions were synthesized using dissolved organic C (DOC) combined with kaolinite (1:1 layer structure) or montmorillonite (2:1 layer structure) clays in the absence or presence of two levels of Fe (III) (named low or high Fe). Flocs were mixed with soil (classified as Luvisol) and incubated with or without ¹³C labelled plant residue (i.e., ryegrass) for 30 days. The CO₂ emissions and DOC concentrations as well as their ¹³C signatures from all treatments were examined. Total C mineralization from flocs was approximately 70% lower than non-flocced DOC. The flocs made with montmorillonite had 16–43% lower C mineralization rate than those made with kaolinite with no Fe or low Fe. However, when flocs were made with high Fe, clay mineralogy did not significantly affect total C mineralization. A positive priming effect (PE) of flocs on native soil OC was observed in all treatments, with a stronger PE found in lower Fe treatments. The high-Fe clay flocs inhibited ryegrass decomposition, while the flocs made without clay had no impact on it. Interestingly, flocs significantly decreased the PE of ryegrass on native soil OC decomposition. These results indicate that the adsorption of DOC onto clay minerals in the presence of Fe (III) stabilizes it against decomposition processes and its stability increases as Fe in flocs increases. Flocs also protect soil OC from the PE of external degradable plant C input. This study showed that Fe level and clay mineralogy play an important role in controlling soil C stability.

有机碳 (OC) 与粘土和金属的相互作用稳定了土壤碳 (C)，但特定粘土-金属-OC 组合物（絮凝体）的影响需要进一步评估。本研究旨在调查受外部 C 输入影响的土壤中絮凝物的稳定性。在不存在或存在两种水平的 Fe (III) (称为低铁或高铁）。将絮状物与土壤（归类为 Luvisol）混合，并在有或没有¹³ C 标记的植物残留物（即黑麦草）的情况下孵育30 天。CO ₂排放量和 DOC 浓度以及它们的¹³检查了所有处理的 C 特征。来自絮凝体的总 C 矿化比非絮凝的 DOC 低约 70%。用蒙脱石制成的絮凝体的 C 矿化率比用不含铁或低铁的高岭石制成的絮凝体低 16-43%。然而，当用高 Fe 制成絮凝体时，粘土矿物学不会显着影响总 C 矿化。在所有处理中都观察到絮体对原生土壤 OC 的正引发效应 (PE)，在较低 Fe 处理中发现更强的 PE。高铁粘土絮凝物抑制了黑麦草的分解，而不含粘土的絮凝物对其没有影响。有趣的是，絮状物显着降低了黑麦草对原生土壤 OC 分解的 PE。这些结果表明，在 Fe (III) 存在的情况下，DOC 吸附到粘土矿物上使其稳定，以防止分解过程，并且其稳定性随着絮体中 Fe 的增加而增加。絮凝物还保护土壤有机碳免受外部可降解植物碳输入的 PE。该研究表明，Fe 水平和粘土矿物学在控制土壤 C 稳定性方面起着重要作用。