Soil carbon (C) saturation implies an upper limit to a soil's capacity to store C depending on the contents of silt + clay and poorly crystalline Fe and Al oxides. We hypothesized that the poorly crystalline Fe and Al oxides in silt + clay fraction increased the C saturation and thus reduced the capacity of the soil to sorb additional C input. To test the hypothesis, we studied the sorption of dissolved organic carbon (DOC) on silt + clay fractions (<53 µm) of highly weathered oxic soils, collected from three different land uses (i.e., improved pasture, cropping and forest). Soils with high carbon saturation desorbed 38% more C than soils with low C saturation upon addition of DOC, whereas adsorption of DOC was only observed at higher concentration (>15 g kg⁻¹). While high Al oxide concentration significantly increased both the saturation and desorption of DOC, the high Fe oxide concentration significantly increased the desorption of DOC, supporting the proposition that both oxides have influence on the DOC sorption in soil. Our findings provide a new insight into the chemical control of stabilization and destabilization of DOC in soil.

中文翻译：

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结晶态的铁和氧化铝含量低会导致土壤中碳饱和度和溶解有机碳的吸附

土壤碳（C）的饱和度意味着土壤储存C的能力的上限，具体取决于淤泥+粘土和结晶度较弱的Fe和Al氧化物的含量。我们假设在粉土和粘土中，结晶度较差的铁和铝氧化物会增加碳饱和度，从而降低土壤吸收额外碳输入的能力。为了验证该假设，我们研究了从三种不同土地用途（即改良的牧场，农作物和森林）收集的高度风化的含氧土壤的粉砂和粘土部分（<53 µm）上的溶解有机碳（DOC）的吸附。碳饱和度高的土壤在添加DOC后比碳饱和度低的土壤多吸收38％的碳，而DOC的吸附仅在较高浓度（> 15 g kg ^-1）。尽管较高的Al氧化物浓度显着增加了DOC的饱和度和脱附，但较高的Fe氧化物浓度显着增加了DOC的脱附，支持了这两种氧化物都对土壤中DOC吸附产生影响的主张。我们的发现为土壤中DOC稳定和去稳定的化学控制提供了新的见识。