Division of Soil and Water Management, KU Leuven, Kasteelpark Arenberg 20, Heverlee, BE, 3001, Belgium.
Facultad de Ciencias de la Vida, Escuela Superior Politécnica del Litoral (ESPOL), Campus Gustavo Galindo Km. 30.5 Vía Perimetral, P.O. Box 09-01-5863, Guayaquil, Ecuador.
J Environ Qual. 2020 Sep;49(5):1359-1369. doi: 10.1002/jeq2.20123. Epub 2020 Aug 3.
Cadmium concentrations in cacao (Theobroma cacao L.) beans from South America often exceed trade limits. Liming soil is advocated as a remediation option, but amendments cannot be incorporated into the entire root zone without harming the trees. An experiment was set up to identify how Cd uptake varies within the root zone when surface and subsurface soil layers are either limed or not. The experiment used 22-cm-height pots with top and bottom layers using surface and subsurface soil samples from a cacao field. The potted soils were either surface limed or not or fully limed and layers spiked with stable Cd isotope in various combinations to trace the plant Cd provenance. The root distribution was neither affected by liming nor by soil source; 70% of the root biomass was present in the top layer. Plants grown on the fully limed surface soil had 1.7 times lower Cd concentrations in leaves than the unlimed treatments, whereas this concentration was 1.2 times lower when only the top layer was limed (surface soil used in both layers). The isotope dilution data showed that surface soil liming enhanced Cd uptake from the unlimed bottom layer compared with the unlimed soil, suggesting compensating mechanisms. The pots containing surface soil over subsurface soil also showed that compensating effect but, due to lower phytoavailable Cd in the subsurface soil, surface liming still effectively reduced foliar Cd. We conclude that liming might be a feasible mitigation strategy, but its effectiveness is limited when Cd phytoavailability remains untreated in the subsurface layer.
南美的可可豆（可可树）中的镉含量经常超过贸易限制。提倡用石灰改良土壤作为一种修复方法，但如果不伤害树木，就不能将改良剂掺入整个根区。进行了一项实验，以确定当表层和次表层土壤分别进行石灰处理或不进行石灰处理时，根区内部的镉吸收量如何变化。该实验使用了 22 厘米高的花盆，上下层分别使用了可可田的表层和次表层土壤样本。盆栽土壤要么进行石灰处理，要么不进行处理，要么完全进行石灰处理，并以各种组合分层添加稳定的镉同位素，以追踪植物的镉来源。根的分布既不受石灰处理的影响，也不受土壤来源的影响；70%的根生物量存在于上层。与未施石灰的处理相比，生长在完全石灰处理的表层土壤上的植物叶片中的镉浓度低 1.7 倍，而当仅顶层进行石灰处理（两层均使用表层土壤）时，该浓度低 1.2 倍。同位素稀释数据表明，与未施石灰的底层相比，表层土壤石灰处理增强了对未施石灰的底层的镉吸收，表明存在补偿机制。含有表层土壤覆盖次表层土壤的花盆也表现出了这种补偿效应，但由于次表层土壤中可利用的镉含量较低，表层石灰处理仍能有效地降低叶片中的镉含量。我们得出的结论是，石灰处理可能是一种可行的缓解策略，但当次表层的镉植物可利用性仍未得到处理时，其效果是有限的。
