镉同位素分馏在土壤-植物体系中的研究进展

Cadmium Isotopes Fractionation in Soil-Plant Systems:A Review

镉污染土壤因其导致粮食作物超标以及通过食物链对居民健康构成威胁,引起了人们的高度关注。土壤镉的迁移转化、植物根部对镉的吸收、植物体内对镉的装载转运和贮存是土壤-植物体系镉生物地球化学循环的重要过程。近年来,稳定同位素分馏技术被广泛应用于土壤-植物系统中镉的迁移和储存,为研究镉在不同土壤库和植物部位中的迁移和转化提供了新的思路和视角。本文首先介绍了镉同位素组成分析的基本原理和方法;其次对土壤矿物溶解、共沉淀、吸附和有机质螯合配位等四个关键过程引起的镉同位素分馏方向和程度进行综述,并重点针对植物根部对镉的吸收、根部-地上部转运和籽粒储存等三个关键过程阐述植物体内镉同位素分馏机制;最后基于目前研究现状,展望了土壤-植物体系镉同位素分馏尚需解决的科学问题和未来的研究方向。有助于深入理解镉在土壤-植物体系中的生物地球化学过程与机制,以期为镉污染土壤的安全利用与治理修复、农产品减毒脱毒等应用技术的研发提供科学依据。

Cd contamination of soils has aroused great concerns among the people the world over for its causing Cd concentration in food crops beyond the limit for food safety,thus posing a threat to human health via the food chain.Migration and transformation of cadmium in soil,uptake of cadmium by plant roots,transport and storage of cadmium in different organs of plants are critical processes of the biogeochemical cycling of cadmium in the soil-plant systems.In recent years,the technique of stable isotope fractionation has been applied to investigation of cadmium transfer and storage in soil-plant systems,providing new insights into the transformation of cadmium in different soil pools and plant compartments.In this study,a brief introduction is presented first to the fundamental principle and methodology of cadmium isotopic composition analysis.And then discussions in detail are made about directions and extents of the cadmium isotopes fractionation in soil induced by a number of processes,such as dissolution of soil minerals,precipitation,adsorption,and chelation with organic matter,with special emphasis laid on mechanisms of the fractionation of Cd in different plant parts during the three critical processes,that is,cadmium uptake by plant roots,cadmium translocation from root to shoot and cadmium storage in grains.To the best of our acknowledge,fractionation of cadmium isotopes in soil-plant systems may be subject to impacts of a number of factors/processes,such as soil minerals,composition of organic matter,root exudates and microorganisms in the rhizosphere,type of plants,stage of plant growth,nutrient elements with antagonistic effect,and so on.However,it remains as of yet unclear as to how.In the end,based on the status quo of the research on cadmium isotopes fractionation in soil-plant systems,perspectives for future research are put forth to encourage a combined application with other techniques,such as spectroscopy-based speciation analyses,molecular biological analyses,and so on,in the hope that the future research may provide a better understanding of the mechanisms of cadmium transformation in soil-plant systems,and help develop regulation strategies and remediation technologies for safe production of crops in cadmium-contaminated soils.