The behavior of trace metals may vary strongly in the course of volcanic soil development. Cadmium retention in soils is specifically important for some Galápagos islands where agriculture is leading to anthropogenic Cd contamination. To assess the influence of soil development factors on soil Cd retention and toxicity, we performed Cd sorption–desorption experiments with volcanic topsoils from the Galápagos Islands sampled along gradients of (a) substrate age (chronosequence, 1.5–1,070 ka) and (b) climate (elevation sequence, 47–866 m asl) ranging from arid lowland areas to humid highland areas. Additionally, the effects of Cd toxicity on the soil microbial community composition were evaluated for two soils of the chronosequence. In young volcanic soils, the sorption capacity was very high but decreased rapidly with soil age and increasing elevation. These trends were coupled with decreases in soil weathering indicators (e.g., electrical conductivity, pH, and effective cation exchange capacity) as well as changes in soil mineralogy. Cadmium addition did not influence total phospholipid fatty acids and basal respiration in most soils. However, with increasing Cd concentration, a pronounced reduction in the Gram-negative/Gram-positive bacteria ratio (from 0.32 to 0.12) occurred in an old, highly weathered soil with low Cd retention capacity. Our results show that up to 60% of added Cd was only weakly sorbed in old volcanic soils. As a consequence, the old volcanic soils of Galápagos bear the potential risk that the mobile Cd fraction is taken up by soil microorganisms, transferring this element into the food chain.

中文翻译：

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加拉帕戈斯群岛沿土壤年龄和气候梯度的火山土壤中的镉保留和微生物反应

在火山土壤发育过程中，痕量金属的行为可能会发生很大变化。土壤中的镉保留对于一些加拉帕戈斯群岛特别重要，这些岛屿的农业导致人为 Cd 污染。为了评估土壤发育因素对土壤 Cd 保留和毒性的影响，我们对来自加拉帕戈斯群岛的火山表土进行了 Cd 吸附-解吸实验，沿 (a) 基质年龄（时间序列，1.5-1,070 ka）和（b）梯度采样气候（海拔序列，47-866 m asl）从干旱的低地地区到潮湿的高地地区。此外，还评估了两种土壤的 Cd 毒性对土壤微生物群落组成的影响。在年轻的火山土壤中，吸附能力非常高，但随着土壤年龄和海拔升高而迅速下降。这些趋势与土壤风化指标（例如，电导率、pH 值和有效阳离子交换能力）的降低以及土壤矿物学的变化相结合。在大多数土壤中，镉的添加不影响总磷脂脂肪酸和基础呼吸。然而，随着 Cd 浓度的增加，革兰氏阴性菌/革兰氏阳性菌的比率显着降低（从 0.32 到 0.12），发生在旧的、高度风化的土壤中，Cd 保留能力低。我们的结果表明，在古老的火山土壤中，高达 60% 的添加 Cd 仅被微弱地吸收。因此，加拉帕戈斯的古老火山土壤具有潜在的风险，即流动的 Cd 部分被土壤微生物吸收，