不同母质土壤-水稻系统Cd吸收累积特征及差异

通过选取土壤有效态镉(Cd)含量相近、母质不同的水稻土河沙泥(河流冲积物发育)和紫泥田(紫色砂页岩母质发育),添加不同浓度的外源Cd(0,0.5,1,2,5mg/kg)模拟Cd污染稻田土壤进行盆栽试验,研究不同母质稻田土壤Cd胁迫条件下水稻不同生育期对Cd吸收累积的差异,并推算出土壤Cd环境安全临界值。结果表明,水稻生育期2种土壤有效态Cd含量均在分蘖期最高,河沙泥有效态Cd含量平均为0.47mg/kg,紫泥田平均为0.36mg/kg,同一外源Cd水平下,河沙泥土壤有效态Cd含量高于紫泥田。对河沙泥而言,随着外源Cd浓度的增加,水稻总生物量呈现先增加后下降的趋势,当外源Cd浓度为1mg/kg时达到最大生物量,为47.11g/pot;而紫泥田水稻生物量呈现逐渐增加的趋势,但各处理间差异不显著(P0.05)。2种土壤中水稻糙米、谷壳、茎叶、根Cd含量均随外源Cd浓度的增加而增加,整体分布特征为根茎叶谷壳糙米,且河沙泥高于紫泥田;河沙泥水稻平均Cd累积量为51.71μg/pot,紫泥田平均Cd累积量为42.56μg/pot,2种土壤成熟期水稻Cd累积量对比分蘖期分别增加1.45,1.07倍。回归分析表明,河沙泥和紫泥田稻米Cd超标的土壤Cd安全临界值分别为2.03,3.14mg/kg。水稻对Cd的吸收累积特征及土壤Cd安全临界值因土壤母质不同而存在显著差异。

Characteristics and Differences of Cadmium Absorption and Accumulation in Different Parent Soil-Rice Systems

Alluvial sandy soil (developed from river alluvium parent materials) and purple clayey soil (developed from purple sandy shale parent materials) with similar available cadmium (Cd) content and different parent materials were selected to conduct pot experiments, and to study the difference of Cd absorption and accumulation at different growth stages of rice under Cd stress conditions in different parent material paddy soils, as well as to calculate the critical value of soil Cd environmental safety. Different concentrations of exogenous Cd (0, 0.5, 1, 2, 5 mg/kg) were added to the soils to simulate the Cd contained paddy soils. The results showed that the available Cd contents of the two soils (alluvial sandy soil and purple clayey soil) were the highest at the tillering stage. The average content of available Cd in alluvial sandy soil was 0.47 mg/kg, and that in purple clayey soil was 0.36 mg/kg. At the same level of exogenous Cd, the content of available Cd in alluvial sandy soil was higher than that in purple clayey soil. For alluvial sandy soil, with the increasing of exogenous Cd concentration, the total biomass of rice increased first and then decreased. When the concentration of exogenous Cd was 1 mg/kg, the biomass was the maximum, which was 47.11 g/pot. While the biomass of rice in purple clayey soil increased gradually, but the difference between the treatments was not significant (P>0.05). The contents of Cd in brown rice, husk, stem and leaf and root increased with the increasing of exogenous Cd concentration in the two soils, and the overall distribution characteristics were root > stem and leaf > husk > brown rice, and the Cd content of alluvial sandy soil was higher than that of purple clayey soil. The average Cd accumulation of rice in alluvial sandy soil was 51.71 g/pot, and it was 42.56 g/pot in the purple clayey soil. Compared with the tillering stage, the Cd accumulation of rice in the two soils increased by 1.45 and 1.07 times at maturation stage, respectively. Regression analysis showed that the critical Cd safety thresholds for Cd-exceeding soil were 2.03 mg/kg and 3.14 mg/kg in alluvial sandy soil and purple clayey soil, respectively. The absorption and accumulation characteristics of Cd and the critical value of soil Cd safety were significantly different among different soil parent materials.