College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, China.
College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, China; Key Laboratory of Plant Nutrition and the Agri-environment in Northwest China, Ministry of Agriculture, Yangling, Shaanxi 712100, China.
Sci Total Environ. 2019 Mar 20;657:871-881. doi: 10.1016/j.scitotenv.2018.12.021. Epub 2018 Dec 4.
Soil dissolved organic matter (DOM) alters heavy metal availability, but whether straw amendment can manipulate soil selenium (Se) speciation and availability through DOM mineralization remains unclear. In this study, allochthonous maize straw and selenate were incubated together in four different soils for 1 y. The transformation and availability of DOM associated Se (DOM-Se) was investigated during aging. Results indicated that soil solution and soil particle surfaces were dominated by hexavalent hydrophilic acid-bound Se (Hy-Se). The amount of fulvic acid bound Se in soil solution (SOL-FA-Se) was higher than humic acid bound Se in soil solution (SOL-HA-Se), except in krasnozems, and mainly existed as hexavalent Se (Se(VI)). Tetravalent Se (Se(IV)) was the main valence state of FA-Se adsorbed on soil particle surfaces (EX-FA-Se) after 5 w of aging. The proportion of soil-available Se (SOL + EX-Se) decreased with increasing straw rate. However, under an application rate of 7500 kg·hm, soluble Se fraction (SOL-Se) reduction was minimal in acidic soils (18.7%-34.7%), and the organic bound Se fraction (OM-Se) was maximally promoted in alkaline soils (18.2%-39.1%). FA and HON could enhance the availability of Se in the soil solution and on particle surfaces of acidic soil with high organic matter content. While Se incorporation with HA could accelerate the fixation of Se into the solid phase of soil. Three mechanisms were involved in DOM-Se aging: (1) Reduction, ligand adsorption, and inner/outer-sphere complexation associated with the functional groups of straw-derived DOM, including hydroxyls, carboxyl, methyl, and aromatic phenolic compounds; (2) interconnection of EX-FA-Se between non-residual and residual Se pools; and (3) promotion by soil electrical conductivity (EC), clay, OM, and straw application. The dual effect of DOM on Se aging was highly reliant on the characteristics of the materials and soil properties. In conclusion, straw amendment could return selenium in soil and reduce soluble Se loss.
土壤溶解有机质（DOM）会改变重金属的有效性，但秸秆添加是否可以通过 DOM 矿化来改变土壤硒（Se）的形态和有效性尚不清楚。本研究在四种不同土壤中共同培养外源玉米秸秆和硒酸盐，共 1 年，研究 DOM 结合硒（DOM-Se）在老化过程中的转化和有效性。结果表明，土壤溶液和土壤颗粒表面主要存在六价亲水性酸结合态硒（Hy-Se）。土壤溶液中腐殖酸结合态硒（SOL-FA-Se）的含量高于土壤溶液中胡敏酸结合态硒（SOL-HA-Se），除黑钙土外，主要以六价硒（Se(VI)）存在。老化 5 周后，土壤颗粒表面吸附的 FA 结合态硒（EX-FA-Se）的主要价态为四价硒（Se(IV)）。随着秸秆添加量的增加，土壤有效硒（SOL+EX-Se）的比例降低。然而，在 7500 kg·hm 的施用量下，酸性土壤中可溶性硒（SOL-Se）的减少量最小（18.7%-34.7%），碱性土壤中有机结合态硒（OM-Se）的增加量最大（18.2%-39.1%）。FA 和 HON 可以促进富含有机质的酸性土壤中土壤溶液和颗粒表面硒的有效性。而 Se 与 HA 结合可以加速 Se 固定到土壤固相。DOM-Se 老化涉及三种机制：（1）与秸秆衍生 DOM 功能基团（羟基、羧基、甲基和芳香酚类化合物）有关的还原、配体吸附和内/外配位；（2）EX-FA-Se 在非残留和残留 Se 库之间的连接；（3）土壤电导率（EC）、粘土、OM 和秸秆施用的促进作用。DOM 对 Se 老化的双重影响高度依赖于材料和土壤特性。总之，秸秆添加可以归还土壤中的硒并减少可溶性硒的损失。
