麦季土壤镉生物有效性对大气臭氧浓度升高的响应

Effect of elevated atmospheric ozone concentration on the bioavailability of Cd in soil during the wheat season

利用开顶式气室(OTCs)设置正常大气和臭氧浓度升高的暴露环境,采用盆栽试验研究不同浓度外源镉污染土壤在小麦生长期间不同深度土层中各形态镉含量的动态变化以及成熟期植株生物量和体内镉含量的变化,同时利用BCR连续提取法和DTPA提取法评价小麦土壤镉生物有效性。结果表明:臭氧熏蒸在各土壤处理均有提高镉生物有效性的趋势,成熟期5mg·kg-1镉污染土壤的镉生物有效性变化显著,其中DTPA-镉含量在0~5、5~10、10~15cm土层分别增加21.82%、16.07%、21.90%,成熟期0~5、5~10cm土层的BCR弱酸溶解态镉分别提高34.83%、47.55%。臭氧熏蒸显著降低无污染土壤暴露组小麦籽粒的生物量(12.22%),却有增加植株各器官镉含量的趋势,其中秸秆部镉含量较对照组显著增加14.75%。臭氧暴露干扰土壤镉的形态分布,促进镉向更易被作物吸收利用的形态转化,增加小麦对镉的吸收累积,最终加剧镉进入食物链的风险。

The objective of this study was to clarify the changes of the bioavailability of Cd in soil affected by atmospheric elevated 03 concentration during the wheat season. Open top chambers （OTCs） were set up as exposure environment with normal atmospheric conditions and atmospheric elevated O3 （40 nmol·mol^-1 higher than ambient 03 concentration）. By adding extrinsic Cd （0, 5 and 50 mg·kg^-1） to soil, the pot experiment was used to study the dynamic changes of Cd in the soil and the changes of plant biomass during the period of wheat growth. The Cd contents in different plant organs were also recorded at the mature period. Soil samples were collected at the 0-5, 5-10 and 10-15 cm depth of topsoil at growth period of seedling, tillering, jointing, heading and maturity respectively. The bioavailability of soil Cd was evaluated by the Community bureau of reference （BCR） sequential extraction and the DTPA extraction method. The results showed that the ozone treatment increased the bioavailability of Cd in all the soil treatments and the difference was significant at 5 mg·kg^-1 Cd treatment during the mature period. Among them the DTPA-Cd contents were increased 21.82M, 16.07M and 21. 900//00 at the topsoil in 0-5, 5-10 and 10-15 cm depth by the ozone treatment, respectively. The weak acid soluble Cd （WAS-Cd） content was increased by the ozone treatment in the maturity period. The increase grew by 34.83% and 47. 55% at the topsoil in 0-5 and 5-10 cm. The ozone fumigation significantly reduced the grain yield of wheat in the treatment of non-polluted soil, with a decrease of 12.22%. However, there was a tendency to increase the Cd content in the organs of plant, which increased 14.75% in wheat straw. The ozone stress interfered the distribution of dif- ferent species of Cd in the soil, promoted the transformation of Cd to the more easily utilized form, increased the absorption and accumulation of Cd by wheat, and eventually exacerbated the risk of Cd entering the food chain.