镉对不同硝酸盐累积型小白菜及根际土壤氮素转化的影响

摘要

Cadmium pollution is a major threat to agricultural ecosystems and safety of agricultural products. To determine the effect of elevated Cd on nitrogen cycling in cabbage-soil system, a pot cultivation experiment was conducted with two cabbage cultivars (L, and H) characterised by possessing lower and higher nitrate accumulating abilities, respectively. The results indicated that two cultivars were not notably impaired when they were applied with low concentration of Cd (0~0.5 mg·kg-1), and in this condition the nitrogen accumulation in cultivar H was higher than cultivar L. The fresh weight of both cultivars were significantly decreased with the increase of Cd. The cultivar H was more sensitive than cultivar L, and the maximum difference reached 20%. Moreover, the nitrogen absorption and utilization of cultivar H was significantly declined in treatments amended with cadmium above 0.5 mg·kg-1, but no significant reduction was detected in cultivar L. When Cd concentration was less than 1.0 mg·kg-1, the nitrate contents in both cultivars decreased, however, they were increased with higher Cd treatment (5.0~10.0 mg·kg-1). The nitrate content of Cultivar H was also sensitively responded to Cd. As the elevation of Cd in soil, Cd content in pakchoi was increased. The accumulated rate of cultivar H decreased slowly when Cd reached 5.0 mg·kg-1. Fitting the relationship of Cd concentration and soil inorganic nitrogen content by using polynomial, we found that soil inorganic nitrogen contents planted withboth cultivars reached the maximum (34.83, 23.73 mg·kg-1) with about 7.1 mg·kg-1 Cd, and cultivar L was higher than H at each treatment. It can be seen that, the cabbage is resistant to low cadmium, but poisoned by higher cadmium, and the specific response differed from different cabbage species. The cultivar L with lower nitrate accumulation ability grew better under cadmium stress. Therefore, it is important to choose appropriate varieties of cabbage, which could help to increase the safety of vegetable production.%镉污染是农业生态和农产品安全的重大威胁。采用盆栽方法，对比分析硝酸盐高、低累积型品种的小白菜Brassica chinens（前者为品种H，抗病矮脚黄；后者为品种L，金夏时青梗菜）对镉污染的响应，探究不同镉水平对小白菜-土壤系统氮素吸收和转化效应，以期为城郊蔬菜的安全生产提供依据。结果表明，在土壤镉质量分数为0~0.5 mg·kg-1时，小白菜生长不受影响，品种间氮素累积量为品种H>品种L。随着镉质量分数的增加，2个品种小白菜生物量均显著降低，品种H单株鲜质量最大降幅达20%，表现更为敏感。镉质量分数高于0.5 mg·kg-1时，显著降低了品种H的氮素吸收和利用，而对低累积品种影响不显著。2个品种小白菜体内硝酸盐含量均在较低的镉质量分数（0.5~1.0 mg·kg-1）处理下有所降低，而当镉质量分数达5.0 mg·kg-1时有所增加，同样是品种H表现更为敏感。随着镉污染水平的增加，小白菜体内镉积累量显著增加，其中品种H在镉质量分数达5.0 mg·kg-1时，累积速率明显降低。通过一元二次模型拟合镉和土壤无机氮质量分数可以得出，镉质量分数为7.1 mg·kg-1时，2个品种小白菜土壤无机氮质量分数均达到最高，分别为34.83和23.73 mg·kg-1。不同品种小白菜在镉污染水平较低时，均具有一定的抗性，而随着镉含量的增加，不同品种对镉毒害响应不同。因此，城郊土壤不同镉污染区域小白菜的种植可依据其品种特性进行选择，从而为蔬菜的生长和土壤的改良提供保障。