不同价态外源硒在石灰性土壤中的形态转化及其生物有效性

Transformation and bioavailability for Pak choi(Brassica chinensis) of different forms of selenium added to calcareous soil

通过盆栽试验和连续浸提的方法,研究了外源硒酸盐(六价硒)和亚硒酸盐(四价硒)施入石灰性土壤后的形态转化及其对小白菜生物有效性的影响.结果表明,不同价态外源硒施入土壤后,土壤各形态硒含量均随外源硒添加量的增加而显著增大(p<0.01).但两种外源硒在土壤中的形态变化明显不同,施入土壤的硒酸盐主要以可溶态形式存在,在土壤中的移动性相对较大;而亚硒酸盐主要以可交换态及碳酸盐结合态形式存在,并可由可溶态转化为其他土壤形态,从而降低了其生物有效性.Monod方程拟合结果表明,小白菜根系对六价硒的亲和能力显著大于四价硒,从而使得硒酸盐处理小白菜地上和地下部最大硒含量分别为亚硒酸盐处理的5倍和2倍,说明在石灰性土壤上硒酸盐比亚硒酸盐的生物有效性更高.另外,亚硒酸盐处理小白菜地下部最大硒含量是地上部的2.3倍,而硒酸盐处理小白菜地下部和地上部最大硒含量相近,说明小白菜根系吸收在硒累积和转运过程中起着至关重要的作用.

The bioavailability of selenium in soils for plants depends more on its forms than on its total content.The aim of this study was to investigate transformation and bioavailability of additional selenite and selenate in calcareous soil to pak choi.A pot experiment was performed and a sequential extraction scheme was used in this study.Content of each selenium species in soil increased significantly with the added selenium（p 0.01）.The main selenium species in selenate-added soil was soluble form,while in selenite-added soil,it was mostly exchangeable and carbonate-bound selenium.Added selenate was hardly fixed by soil,and hence had relatively higher mobility than selenite in soil.Added selenite could transform from the soluble form to the other three forms,which would decrease its bioavailability.Monod model fitting results showed that the affinity of pak choi roots to selenate was larger than selenite.Estimated maximal selenium contents of pak choi shoots and roots in selenate-treated soils were 5 times and 2 times larger than in selenite-treated soils.In selenite-treated soils,estimated maximal selenium content of pak choi roots was 2.3 times larger than that in shoots,while in selenate-treated soils,the estimated maximal selenium contents of pak choi shoots and roots were approximately the same.In pak choi roots,adsorption was the dominant selenium accumulation method.In conclusion,selenate has higher bioavailability than selenite in calcareous soil.