Hormetic responses in soil ecosystem are increasingly reported recently. Soil enzymes are involved in almost all biochemical reactions, but insufficient investigations were conducted to define its hormetic responses. The objective of this study is to investigate the hormetic responses across soil particle–size fractions with cadmium (Cd) as a stressor and alkaline phosphatase (ALP) as a potential endpoint. Soils were treated by adding CdCl₂·2.5H₂O solution with 0, 0.003, 0.03, 0.3, 3.0 and 30.0 mg·kg^− 1 of Cd, respectively. A low–power ultrasonic method was used to separate the bulk soil into 0.1–2, 2–63, 63–200 and 200–2000 μm fractions. In 2–63 μm, ALP activity at doses of 0.3–3.0 mg·kg^− 1 of Cd was significantly higher than that of CK (0.0 mg·kg^− 1 of Cd), showing a typical U–shaped dose–response with the amplitude of 72.3–118.6%. Similarly, ALP activity at 0.003–0.3 mg·kg^− 1 of Cd was 36.4–66.1% higher than that of CK in 63–200 μm. However, no similar phenomenon was observed in 0.1–2 and 200–2000 μm fractions. This suggested that low doses of Cd induced the hormetic responses of soil ALP, particularly in 2–63 and 63–200 μm. In addition, analysis of the microbial community structure and diversity indicates that, at genus level, the relative abundance (RA) of Gillisia at 0.03–0.3 mg·kg^− 1 of Cd was significantly higher than that of CK with the amplitude of 3.7–37.5% in 2–63 μm. The similar responses were observed that the RA of Pontibacter at 0.003–0.03 mg·kg^− 1 of Cd was 4.0–85.4% higher than that of CK in 63–200 μm. This showed that Gillisia and Pontibacter possibly contribute to the hormetic responses of soil ALP when low contents of Cd presented in soils. This study will provide a good insight into the hormetic phenomenon at soil ecosystem scales.

中文翻译：

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在典型的沿海湿地中，Cd对不同粒度级分的土壤碱性磷酸酶的抑制作用

近来越来越多地报道了土壤生态系统中的反应式反应。土壤酶几乎参与了所有生化反应，但是没有进行足够的研究来确定其酶促反应。这项研究的目的是研究以镉（Cd）为胁迫源和碱性磷酸酶（ALP）为潜在终点的土壤颗粒级分的滴定反应。通过分别添加0、0.003、0.03、0.3、3.0和30.0 mg·kg ^-1的Cd的CdCl ₂ ·2.5H ₂ O溶液处理土壤。使用低功率超声方法将散装土壤分成0.1–2、2–63、63–200和200–2000μm的级分。在2-63μm，剂量为0.3–3.0 mg·kg ^{− 1时}ALP活性Cd的含量显着高于CK（0.0 mg·kg ^-1的Cd），显示出典型的U形剂量反应，幅度为72.3–118.6％。同样，在63-200μm的镉中，0.003–0.3 mg·kg ^-1的ALP活性比CK高36.4–66.1％。但是，在0.1–2和200–2000μm的馏分中未观察到类似现象。这表明低剂量的镉会引起土壤ALP的刺激反应，特别是在2-63和63-200μm范围内。此外，对微生物群落结构和多样性的分析表明，在属水平上，0.03–0.3 mg·kg ^{− 1}的菌根的相对丰度（RA）Cd的含量显着高于CK，在2–63μm中的振幅为3.7–37.5％。观察到类似的反应，在63-200μm的镉中0.003–0.03 mg·kg ^-1的庞蒂杆菌的RA比CK高4.0–85.4％。这表明Gillisia和Pontibacter可能有助于土壤ALP的毒物兴奋反应时，镉含量低的土壤中呈现。这项研究将提供对土壤生态系统规模上的钟表现象的深入了解。