摘要
重金属污染对粮食安全及人体健康造成巨大威胁，目前已开发出许多农田重金属污染修复方法。硒的补充显著降低作物对重金属的吸收，同时促进作物在重金属污染土壤中的生长，施硒已成为阻控作物吸收重金属的新途径。本文对施硒阻控作物吸收重金属的5种机制即硒改变土壤重金属的生物有效性、硒与重金属竞争植物摄取通道、硒促进植物根系铁膜形成、硒诱导植物根系形态及结构变化、硒调控植物重金属螯合和转运基因表达等研究进展进行了综述，同时对施硒阻控作物吸收重金属潜在风险及未来研究重点进行展望，以期为将来利用硒作为重金属阻控剂提供参考。
矿山的开采、过度使用化肥和杀虫剂以及污水灌溉等人为活动会导致农田土壤严重的重金属及类金属污
施加到土壤中的硒会与土壤重金属发生复杂的相互作用，从而改变土壤重金属的生物有效
图1 硒改变土壤重金属的生物有效性
Fig.1 Selenium alters the bioavailability of heavy metals in soil
水稻种植涉及淹水及排水2种水分管理方式，稻田土壤的Eh变化对硒及土壤重金属的生物有效性有着重要影
除土壤pH、Eh等理化性质外，土壤微生物可通过对硒及土壤重金属的转化介导形成不溶性硒化物沉淀，最终降低重金属的生物有效性（
除了直接改变土壤重金属的生物有效性之外，硒还可以通过与砷等类金属竞争离子摄取通道从而降低作物中类金属的含
图2 硒阻控作物吸收重金属的机制（改自文献［
Fig.2 Mechanism of selenium in mitigating heavy metal uptake by crops（modified form reference［
铁膜是水稻等水生植物根表由铁的氧化物或氢氧化物形成的铁斑块，对As、Cd、Hg、Sb、Zn及Cu等重金属均有较强吸附能力，已被广泛报道作为植物吸收重金属的屏
除以上因素外，硒的施加剂量、价态及施加时机均会影响硒对植物根表铁膜形成及重金属阻控效果。Chang
根系的形态及结构对植物抵御重金属的毒性和胁迫起着重要作
除了诱导植物根系形态或结构的改变外，硒还可通过改变根系细胞壁组成成分介导重金属的阻控。细胞壁主要由纤维素、半纤维素、果胶、木质素等物质组成，可通过与重金属的结合作用降低植物根系对重金属的吸
除上述机制外，硒还可通过调控植物重金属螯合和转运相关基因的表达进而降低重金属的吸收和毒性（
尽管施加硒阻控植物吸收各种重金属的效果得到广泛的验证，以亚硒酸盐为主要成分的重金属叶面阻隔剂也得到一定的应用，但是使用硒修复重金属污染也存在潜在的风
在某些条件下，硒可能改变植物吸收重金属元素的价态，因而影响硒对重金属的修复效果。有研究发现，尽管施加硒显著降低水稻籽粒中总砷的含量，但却提高了稻米中As（Ⅲ）的含量，而As（Ⅲ）的毒性远高于As（Ⅴ
施硒作为一种硒强化手段，不仅能促进作物富硒，提升作物品质，同时也在阻控作物重金属吸收方面展现出良好的应用前景。由于土壤-植物体系的复杂性，不同的作物及土壤的性质、重金属污染程度等因素均会影响硒对重金属的修复效果，硒降低植物重金属吸收机制的研究需要更深入的研究。未来的研究有以下几个重点：（1）需进一步明确土壤中不同形态的Se与重金属的互作机制，阐释多大剂量的Se能阻控作物重金属的积累；（2）进一步探究土壤pH、Eh、有机质等理化因子如何影响硒修复重金属的效果；（3）探究硒的施加量对不同作物吸收重金属的阻控效果，优化出阻控特定作物吸收重金属的安全硒施加剂量；（4）除Se（Ⅳ）及Se（Ⅵ）外，纳米硒毒性更小且容易被植物吸收，需开展更多纳米硒阻控植物吸收重金属的研究；（5）除镉之外，硒如何在基因水平调控植物摄入及转运其他重金属的机制尚不明确，有待进一步的阐释；（6）实际重金属复合污染土壤多为复合污染，硒对复合污染如砷镉共污染的修复效果的研究鲜有报道，需更多的研究；（7）施加硒对土壤微生物群落和重金属转化功能菌株的影响少有研究，硒对土壤生态平衡的影响尚不明确。通过对硒阻控植物吸收重金属机制的阐释，不仅能实现对毒性重金属精准高效阻控，同时能避免硒施加所带来的潜在风险。
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