Soil liming to lower cadmium (Cd) bioavailability is challenged in perennial cacao orchards by the low penetration of lime in soils, not reaching deeper roots. Some studies suggest that gypsum (CaSO₄) could reduce Cd uptake by enhanced Ca²⁺:Cd²⁺ competition at the root surface. A pot experiment was conducted to identify soil conditions affecting gypsum efficacy in cacao plantlets (5-month-old CCN-51). Plants grew for 115 days in soils sampled from six locations with variable cation exchange capacity (CEC, 6–50 cmol_c.kg⁻¹) and soil solution Ca²⁺ (1.3–17 mM). Soils were either mixed or not mixed with a dose equivalent to 4.0 Mg gypsum ha⁻¹. Leaf Cd concentration in plants grown on gypsum applied soils was statistically lower compared to unamended soils in only one of the six soils. The reduction factor of leaf Cd concentrations due to gypsum (RF = control/amended Cd concentration ratio) ranged from 2.32 (high effect) to 0.76 (no effect), and it was positively correlated with the Ca²⁺ in the solution of the unamended soil (R² = 0.58) and with increasing CEC (R² = 0.52), that is, gypsum only reduced Cd bioavailability in high CEC soils, confirming a trend found in earlier publications. Soil solution analyses showed that gypsum application enhanced total dissolved Cd by forming CdSO₄⁰ complexes with, in some cases, even enhanced Cd²⁺ ion activities, likely related to Ca²⁺-induced Cd²⁺ mobilisation. Data suggest that Ca²⁺ derived from gypsum has counteracting effects on Cd mobilisation and ion competition at the root surface. The former reactions are less pronounced in high CEC soils. More research is needed to unravel gypsum effects on high Ca²⁺ soils to corroborate our findings.

中文翻译：

---

石膏应用仅降低阳离子交换能力高的土壤中可可对镉的吸收：土壤化学分析

由于石灰在土壤中的渗透率低，无法到达更深的根部，因此在多年生可可园中，土壤石灰化以降低镉 (Cd) 的生物有效性面临挑战。一些研究表明，石膏 (CaSO ₄ ) 可以通过增强根表面的Ca ²⁺ :Cd ²⁺竞争来减少 Cd 的吸收。进行盆栽试验以确定影响可可幼苗（5 个月大的 CCN-51）中石膏功效的土壤条件。植物在从六个具有不同阳离子交换能力（CEC，6-50 cmol _c .kg ^-1）和土壤溶液 Ca ²⁺ (1.3-17 mM) 的位置取样的土壤中生长了 115 天。土壤与相当于 4.0 Mg 石膏 ha ^{-1的剂量混合或不混合}. 与仅在六种土壤之一中的未改良土壤相比，在施用石膏的土壤上生长的植物中的叶片 Cd 浓度在统计学上较低。石膏对叶片 Cd 浓度的降低因子（RF = 对照/修正 Cd 浓度比）范围为 2.32（高影响）至 0.76（无影响），与未修正溶液中的Ca ²⁺呈正相关。土壤（R ²  = 0.58）和随着 CEC 的增加（R ²  = 0.52），即石膏仅降低高 CEC 土壤中 Cd 的生物有效性，证实了早期出版物中发现的趋势。土壤溶液分析表明，石膏施用通过与在某些情况下甚至增强 Cd ^{2+形成 CdSO} ₄ ^{0复合物来提高总溶解 Cd}离子活性，可能与 Ca ²⁺诱导的 Cd ²⁺动员有关。数据表明，来自石膏的 Ca ^{2+对根表面的 Cd 动员和离子竞争具有抵消作用。}前一种反应在高 CEC 土壤中不太明显。需要更多的研究来揭示石膏对高 Ca ²⁺土壤的影响，以证实我们的发现。