Institute of Terrestrial Ecosystems, Swiss Federal Institute of Technology, Zurich, Switzerland.
Institute of Terrestrial Ecosystems, Swiss Federal Institute of Technology, Zurich, Switzerland.
Sci Total Environ. 2017 Feb 15;580:677-686. doi: 10.1016/j.scitotenv.2016.12.014. Epub 2016 Dec 28.
Cadmium (Cd) uptake by cocoa has recently attracted attention, after the European Union (EU) decided to establish values for tolerable Cd concentrations in cocoa products. Bean Cd concentrations from some cocoa provenances, especially from Latin America, were found to exceed these values. Cadmium uptake by cocoa is expected not only to depend on a variety of soil factors, but also on plant and management factors. In this study, we investigated the influence of different production systems on Cd uptake by cocoa in a long-term field trial in the Alto Beni Region of Bolivia, where cocoa trees are grown in monocultures and in agroforestry systems, both under organic and conventional management. Leaf, fruits and roots of two cultivars were sampled from each production system along with soil samples collected around these trees. Leaf, pod husk and bean samples were analysed for Cd, iron (Fe) and zinc (Zn), the roots for mycorrhizal abundance and the soil samples for 'total' and 'available' Cd, Fe and Zn as well as DGT-available Cd and Zn, pH, organic matter, texture, 'available' phosphorus (P) and potassium (K). Only a small part of the variance in bean and pod husk Cd was explained by management, soil and plant factors. Furthermore, the production systems and cultivars alone had no significant influence on leaf Cd. However, we found lower Cd leaf contents in agroforestry systems than in monocultures when analysed in combination with DGT-available soil Cd, cocoa cultivar and soil organic matter. Overall, this model explained 60% of the variance of the leaf Cd concentrations. We explain lower leaf Cd concentrations in agroforestry systems by competition for Cd uptake with other plants. The cultivar effect may be explained by cultivar specific uptake capacities or by a growth effect translating into different uptake rates, as the cultivars were of different size.
镉（Cd）的摄取量最近引起了人们的关注，此前欧盟（EU）决定为可可制品中可容忍的 Cd 浓度建立值。来自某些可可起源地的豆 Cd 浓度，特别是来自拉丁美洲的豆 Cd 浓度，被发现超过了这些值。可可对 Cd 的摄取量不仅预计不仅取决于各种土壤因素，还取决于植物和管理因素。在这项研究中，我们在玻利维亚 Alto Beni 地区的一个长期田间试验中调查了不同生产系统对可可中 Cd 摄取量的影响，在该地区，可可树种植在单一栽培和农林系统中，均采用有机和常规管理。从每个生产系统中采集两种品种的叶片、果实和根，以及围绕这些树采集的土壤样品。对叶片、荚壳和豆样进行 Cd、铁（Fe）和锌（Zn）分析，对根进行菌根丰度分析，对土壤样品进行“总”和“有效”Cd、Fe 和 Zn 以及 DGT-有效 Cd 和 Zn、pH 值、有机质、质地、“有效”磷（P）和钾（K）分析。豆和荚壳 Cd 的变异只有一小部分可以用管理、土壤和植物因素来解释。此外，生产系统和品种本身对叶片 Cd 没有显著影响。然而，当与 DGT-有效土壤 Cd、可可品种和土壤有机质结合分析时，我们发现农林系统中的 Cd 叶含量低于单一栽培系统。总体而言，该模型解释了叶片 Cd 浓度变异的 60%。我们解释了农林系统中较低的叶片 Cd 浓度，因为与其他植物竞争 Cd 摄取。品种效应可能是由于品种特定的摄取能力或生长效应转化为不同的摄取率，因为品种大小不同。
