富硒土壤腐殖质特征及对芥菜富集重金属的影响效应

It is meaningful to develop selenium-rich vegetables on the rich selenium soil in Haikou. However, selenium-rich soil is often associated with heavy metal , which is a threat to the safety of the vegetables. Soil Organic Matter (SOM) is an important component of soils. Humus as the main form of SOM contains a large number of carboxyl, hydroxyl and other functional groups, it has strong adsorption and complexation to heavy metals and thus makes a key impact on heavy metal enrichment in vegetables.Therefor, taking the leaf mustard and its soil in selenium-rich areas of Haikou as the research object, samples of leaf mustard and its soil with different selenium levels were obtained through field sampling and pot experiment. (1)Extracting Fulvic Acid(FA),Humic Acid(HA) and Humin(Hu) from soil samples, then investigating the characteristics of humus in selenium-rich soils, including the composition, structure and behavior characteristics.(2)By comparing the distribution of typical heavy metal(Cd,Pd,Cu,Zn) in the rhizosphere, tillage soil, leaf mustard root and the edible parts in soil- leaf mustard system of different selenium levels, it reveals the characteristics of enrichment of heavy metals in selenium-rich soil- leaf mustard system.(3)With the characteristics of humus in selenium-rich soil and the characteristics of heavy metal enrichment in selenium-rich soil- leaf mustard system, based on data of soil physical and chemical properties, the relationship between them was analyzed and the correlation and significance were compared,which reveal the effects of the characteristic of humus in selenium-rich soil to the enrichment of heavy metal in leaf mustard and the mechanism.

海口依托富硒土壤开发富硒蔬菜意义重大，但富硒土壤常伴生重金属威胁蔬菜安全。因土壤有机质是土壤重要组成成分，而腐殖质作为土壤有机质存在的主要形态含有大量的羧基、羟基等官能团，对重金属有较强的吸附、络合作用，进而对蔬菜富集重金属的行为有关键影响。为此，以海口富硒区主栽的芥菜及其土壤为研究对象，通过大田采样和盆栽试验获取不同硒水平土壤及芥菜样品，（1）对土壤样品提取富里酸、胡敏酸和胡敏素，探讨富硒土壤腐殖质特征，包括组成、结构与行为特征。（2）比较不同硒水平土壤-芥菜系统中典型重金属（Cd、Pb、Cu、Zn）在根际及耕作层土、芥菜根及可食用部的分布，揭示富硒土壤-芥菜系统中重金属的富集性特征。（3）联系富硒土壤腐殖质特征和富硒土壤-芥菜系统中重金属的富集性特征，结合土壤理化性状的数据，分析其相互关系和影响规律，比较其相关性和显著性差异等，揭示富硒土壤腐殖质特征对芥菜富集重金属的影响效应及机制。

富硒土壤是富硒农产品开发的重要资源，往往伴生重金属，需防控其污染风险。以海口富硒区芥菜及土壤为对象。（1）以大田采样和盆栽试验获取样品。（2）富硒土壤腐殖质特征研究。比较两种方式获得土壤样品，腐殖质组成差异较大，且盆栽土壤富里酸（FA）、胡敏酸（HA）、胡敏素（HM）中各元素（C、N、H、S）含量变动较大。（3）土壤腐殖质对重金属的作用及对芥菜富集重金属的影响效应。①大田采样表明，FA、HA对溶液中Pb、Cd、Cu、Cr均产生吸附作用，硒水平较高土壤提取FA/HA对重金属作用较明显；HM对土壤重金属有钝化作用，且硒水平高土壤提取HM钝化较强，其机制是形态转化作用；硒水平高土壤提取腐殖质对Pb、Cd作用较强，具有较明显钝化效应；富硒土壤硒与铅、镉具伴生效应，而土壤硒对芥菜中铅、镉富集具抑制作用，可降低其污染风险，其机制与腐殖质能降低土壤铅、镉形态活性有关。②不同外源硒水平下盆栽试验表明，外源硒水平在HA/FA与Pb2+、Cd2+吸附过程中的影响有所不同，说明Se与HA/FA相互结合强度有差异且存在竞争吸附作用；HA对Pb2+吸附率较大（39.95％），而FA对Cd2+吸附率较大（31.15%），Langmuir模型较好地拟合HA和FA对Pb2+的吸附，而Freundlich模型较好地拟合FA对Cd2+吸附；比较HM，α-Fe2O3和HM-α-Fe2O3作为土壤重金属钝化剂效果，与钝化剂用量、钝化时间呈现较好线性增长关系，施用率低且效果明显，HM适用于短期修复，而HM-α-Fe2O3适用于长期修复；土壤中硒水平、腐殖质含量和Pb/Cd浓度之间均呈负相关，反映了其相互之间的抑制作用，也解释了土壤-芥菜系统中随外源硒水平提高Pb、Cd活性及其积累性降低现象。③不同价态外源Se（II）、Se（IV）、Se（VI）下盆栽试验表明，提取出FA对Pb2+吸附量较大，其中，添加Se（IV）土壤的富里酸对Pb2+吸附量最大（84.4%），用Freundlich和Langmuir模型均能较好对数据进行拟合，符合伪二级动力学方程，说明化学吸附占主导；以土壤重金属DTPA提取态、Tessier形态和DGT浓度表征铅、镉活性，均表明加入不同价态外源硒后，均降低土壤中重金属活性，其中以Se（VI）对铅、Se（II）对镉钝化作用较显著。以上所揭示规律，可为指导富硒区重金属污染防控提供重要科学数据。