Cadmium uptake, accumulation, and remobilization in iron plaque and rice tissues at different growth stages.

Rice consumption is considered the main source of human dietary Cd intake in Southeast Asia. This study aimed to investigate Cd uptake, accumulation, and remobilization in iron plaque and rice (Oryza sativa L. cv. 'Xiangwanxian 12') tissues at different growth stages. A pot experiment was performed in two Cd-contaminated paddy soils. Cd concentrations in iron plaque and rice tissues at five different growth stages (tillering, booting, milky, dough, and maturing) were measured. Cd concentrations in iron plaque and rice tissues (roots, stems, leaves, spikelet, husks, and brown rice) varied with growth stage. Cd accumulation in rice plants increased with extending growth in both soils, reaching 15.3 and 35.4µg/pot, respectively, at the maturing stage. The amounts of Cd in brown rice increased from the milky to maturing stages, with the greatest percentage uptake during the maturing stage. Cd amount in iron plaque significantly affected the uptake and accumulation of Cd in roots and aerial parts of rice plants. Accumulated Cd in leaves was remobilized and transported during the booting to maturing stages, and the contributions of Cd transportation from leaves to brown rice were 30.0% and 22.5% in the two soils, respectively. A large amount of Cd accumulated in brown rice during the maturing stage. The transportation of remobilized Cd from leaves was also important for the accumulation of Cd in brown rice.

[Impacts of Silicon Fertilizer as Base Manure on Cadmium Bioavailability in Soil and on Cadmium Accumulation in Rice Plants].

The impacts of silicon (Si) on cadmium (Cd) bioavailability in soil and Cd accumulation in rice plants were investigated in pot experiments with rice (Oryza sativa L.) cultivation. Silicon fertilizer as the base manure (Si 0, 15, 30, and 60 mg·kg-1) was added in simulated slightly Cd-contaminated soil (total soil Cd of 0.72 mg·kg-1) and severe Cd-contaminated soil (total soil Cd of 5.08 mg·kg-1). It indicated that the application of 15-60 mg·kg-1 Si before the rice was transplanted improved soil pH values and reduced the contents of exchangeable-Cd and TCLP extractable-Cd in the soil by 24.2%-43.7% and 12.7%-46.8%, respectively, during the rice growing stages. The reduction in soil Cd bioavailability resulted from the complexing of Si and Cd, and the reduction followed the order:slightly Cd-contaminated soil > severely Cd-contaminated soil. It was obvious that silicon fertilizer improved rice biomass above ground, especially for rice grain yield. In the slightly Cd-contaminated soil, Si both promoted and restrained soil Cd transportation from the rice root to the shoot; the low application (Si 15 mg·kg-1) and high application (Si 60 mg·kg-1) of Si both promoted Cd transportation, but the medium application (Si 30 mg·kg-1) restrained Cd transportation. With increasing silicon fertilizer application, Cd contents in brown rice increased first and then decreased, ranging from 0.07-0.15 mg·kg-1, remaining lower than 0.2 mg·kg-1. In the severely Cd-contaminated soil, Si restrained the soil Cd transportation from the rice root to the shoot. The Cd contents in brown rice, husk, and straw were reduced by 38.7%-48.5%, 35.7%-70.7%, and 30.9%-40.7%, respectively, and Cd contents in brown rice were 0.23-0.28 mg·kg-1. Considering rice grain yields and Cd contents in brown rice, it was recommended that the Si application be 30 mg·kg-1 of Si in the slightly Cd-contaminated soil and Si 15-60 mg·kg-1 in the severely Cd-contaminated soil.

[Remedying Effects of a Combined Amendment for Paddy Soil Polluted with Cd for Spring and Autumn Rice].

An in-situ paddy experiment was conducted to study the remedying effects of a combined amendment(calcium carbonate+diatomite+ferric sulfate) on Cd bioavailability in soil and Cd accumulation in rice for spring and autumn rice planted in a certain Cd contaminated paddy soil in Beishan Town, Changsha, Hunan Province. The results showed that:Application of the combined amendment significantly increased soil pH and CEC values in both cultivated seasons, but decreased soil OM contents for the spring rice. During the experiment, the contents of TCLP-extractable Cd and CaCl2-extractable Cd in soil were reduced by 18.0%-33.0% and 5.4%-57.9%, respectively. The Cd contents in brown rice, husk, leave and root for the spring rice decreased by 29.6%-56.1%, 52.1%-54.0%, 18.1%-80.7% and 24.4%-41.6%, respectively, due to application of the combined amendment. There were significant differences in Cd transport capacity between spring rice and autumn rice, and the transportation of soil Cd in autumn rice was smoother than that in spring rice. For the autumn rice, the effects of the combined amendment were not significant(P>0.05), except that the Cd content in husk increased a little after applying 2 g·kg-1 of the combined amendment. Significant positive correlations were found between the Cd contents in brown rice and the contents of TCLP-extractable Cd or CaCl2-extractable Cd in soil. Application of the combined amendment effectively inhibited Cd uptake by rice root and reduced Cd content in brown rice for the spring rice; however, these remedying effects were significantly weakened for the autumn rice due to loss of the combined amendment with the movement of irrigation water in the spring season. Therefore, we suggest that supplement of the combined amendment is necessary between two rice cultivated seasons.