Aluminous clay and pedogenic Fe oxides modulate aggregation and related carbon contents in soils of the humid tropics
Aluminous clay and pedogenic Fe oxides modulate aggregation and related carbon contents in soils of the humid tropics
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DOI：
10.5194/soil-7-363-2021
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发表时间：
2021-07
期刊：
影响因子：
6.8
通讯作者：
M. Kirsten;R. Mikutta;D. Kimaro;K. Feger;K. Kalbitz
中科院分区：
文献类型：
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作者：
M. Kirsten;R. Mikutta;D. Kimaro;K. Feger;K. Kalbitz
摘要。团聚体广泛影响土壤的物理和生物地球化学性质，对土壤碳储量有积极影响。对于风化的热带土壤，铝质粘土（高岭石和三长石）和成土铁（氧合）氧化物（针铁矿和赤铁矿；称为“铁氧化物”）被认为是团聚体的重要组成单元。然而，由于铝硅酸盐，氢氧化铝和氧化铁是粘土大小的部分的一部分，很难分离某些矿物相如何调节聚集。此外，目前尚不清楚这将对土地利用变化后有机碳（OC）持久性产生什么影响。我们选择了坦桑尼亚东部乌桑巴拉山脉在森林和农田土地利用下具有独特矿物学成分的表土，其铝粘土和铁氧化物的含量各不相同。在不同的矿物学组合中，我们确定了团聚体粒度分布、团聚体稳定性、团聚体粒度组分的有机碳含量，以及森林和农田利用下团聚体和有机碳含量的变化。不同矿物学组合（高水平的大团聚体和高团聚体稳定性）的土壤团聚体模式相当相似。然而，我们发现了一些统计上显著的铝粘土和成土铁氧化物对聚集和OC储存的影响。铝质粘土含量为250 g kg - 1，成土铁含量为4 mm。相比之下，当成土铁含量低于60 g kg - 1时，铝质粘土含量低于250 g kg - 1，即使在农业使用下，也能促进碳的储存和持久性。低铝质粘土和高成土铁含量的组合表现出最高的有机碳持久性，尽管林改田造成了大量的分解。这表明，这些热带土壤中的团聚体受到矿物学制度的调节，导致团聚体大小分布的适度但显著的差异。然而，在这些高度风化的土壤中，聚集性对总体有机碳持久性的影响不大，在这些土壤中，有机碳储存更多地受到直接矿物-有机相互作用的调节。
Abstract. 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 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.