Aggregation affects a wide range of physical and biogeochemical soil properties with positive effects on soil carbon storage. For weathered tropical soils, aluminous clays (kaolinite and gibbsite) and pedogenic Fe (oxyhydr)oxides (goethite and hematite; termed “Fe oxides”) have been suggested as important building units for aggregates. However, as aluminosilicates, aluminum hydroxides, and Fe oxides are part of the clay-sized fraction it is hard to separate how certain mineral phases modulate aggregation. In addition, it is not known what consequences this will have for organic carbon (OC) persistence after land-use change. We selected topsoils with unique mineralogical compositions in the East Usambara Mountains of Tanzania under forest and cropland land uses, varying in contents of aluminous clay and Fe oxides. Across the mineralogical combinations, we determined the aggregate size distribution, aggregate stability, OC contents of aggregate size fractions, and changes in aggregation and OC contents under forest and cropland land use. Patterns in soil aggregation were rather similar across the different mineralogical combinations (high level of macroaggregation and high aggregate stability). Nevertheless, we found some statistically significant effects of aluminous clay and pedogenic Fe oxides on aggregation and OC storage. An aluminous clay content > 250 g kg⁻¹ in combination with pedogenic Fe contents < 60 g kg⁻¹ significantly promoted the formation of large macroaggregates > 4 mm. In contrast, a pedogenic Fe content > 60 g kg⁻¹ in combination with aluminous clay content of < 250 g kg⁻¹ promoted OC storage and persistence even under agricultural use. The combination with low aluminous clay and high pedogenic Fe contents displayed the highest OC persistence, despite conversion of forest to cropland causing substantial disaggregation. This indicates that aggregation in these tropical soils is modulated by the mineralogical regime, causing moderate but significant differences in aggregate size distribution. Nevertheless, aggregation was little decisive for overall OC persistence in these highly weathered soils, where OC storage is more regulated by direct mineral–organic interactions.

中文翻译：

---

铝粘土和土壤铁氧化物调节湿热带土壤中的聚集和相关碳含量

聚集影响广泛的物理和生物地球化学土壤特性，对土壤碳储存有积极影响。对于风化的热带土壤，铝粘土（高岭石和三水铝石）和成土的 Fe（羟基）氧化物（针铁矿和赤铁矿；称为“Fe 氧化物”）已被建议作为骨料的重要构建单元。然而，由于铝硅酸盐、氢氧化铝和 Fe 氧化物是粘土大小部分的一部分，因此很难区分某些矿物相如何调节聚集。此外，尚不清楚这将对土地利用变化后有机碳 (OC) 的持久性产生什么后果。我们在坦桑尼亚东部乌桑巴拉山脉的森林和农田土地利用下选择了具有独特矿物组成的表土，其铝粘土和铁氧化物的含量各不相同。在矿物学组合中，我们确定了森林和农田土地利用下的聚集体尺寸分布、聚集体稳定性、聚集体尺寸部分的 OC 含量以及聚集体和 OC 含量的变化。不同矿物组合的土壤团聚模式相当相似（高水平的大团聚和高团聚稳定性）。尽管如此，我们发现铝粘土和成土铁氧化物对聚集和 OC 储存有一些统计上的显着影响。铝粘土含量 不同矿物组合的土壤团聚模式相当相似（高水平的大团聚和高团聚稳定性）。尽管如此，我们发现铝粘土和成土铁氧化物对聚集和 OC 储存有一些统计上的显着影响。铝粘土含量 不同矿物组合的土壤团聚模式相当相似（高水平的大团聚和高团聚稳定性）。尽管如此，我们发现铝粘土和成土铁氧化物对聚集和 OC 储存有一些统计上的显着影响。铝粘土含量>  250 g kg ^-1结合成土铁含量<  60 g kg ^-1显着促进了>  4 mm的大团聚体的形成。相比之下，成土 Fe 含量>  60 g kg ^-1与铝粘土含量<  250 g kg ^-1 即使在农业使用下也促进了 OC 的储存和持久性。尽管将森林转化为农田导致大量分解，但低铝粘土和高成土铁含量的组合显示出最高的 OC 持久性。这表明这些热带土壤中的聚集受到矿物学制度的调节，导致聚集体大小分布适度但​​显着差异。然而，在这些高度风化的土壤中，聚集对整体 OC 的持久性几乎没有决定性，其中 OC 的储存更多地受直接矿物 - 有机相互作用的调节。