[Effects of Nano Material on Cadmium Accumulation Capacity and Grain Yield of Indica Hybrid Rice Under Wetting-drying Alternation Irrigation].

Wetting-drying alternation irrigation (WDI) can harvest high grain yield under effective irrigation water saving conditions. However, the kernel cadmium (Cd) content usually exceeds the national standard of 0.20 mg Cd per kg kernel in WDI. Applying a passivating agent with high-efficient repairing capabilities could be a feasible approach to reduce Cd content lower than 0.20 mg·kg-1 in WDI. Therefore, a field experiment was conducted with different irrigation regimes and passivating agents in a mildly Cd-polluted paddy field, of which the irrigation regimes were WDI and traditional flooded irrigation (FI) and the six passivating agents treatments were CK (no passivating agent; T1), slaked lime with 1125 kg·hm-2(T2), 1125 kg slaked lime and 3000 kg biochar per hectare (T3), 1125 kg slaked lime and 3000 kg organic fertilizer per hectare (T4), 1500 kg porous Nano stupalith per hectare (T5), and 1125 kg slaked lime combined with 1500 kg porous Nano stupalith per hectare (T6). Two typical Indica hybrid rice varieties with a high accumulated capacity named cultivar Shenliangyou 1813 and a low accumulated trait named cultivar Liangyou 6206 were utilized. The main reason that Indica hybrid rice cultivars were selected was their higher absorbed and accumulated characteristics than that of Japonica rice. The results indicated that available Cd content of the soil significantly declined with 17.13%-61.01% decreasing amplitude at maturity when compared with pre-transplanting in WDI; however, the reduction was in the range of -43.45%-21.07% for the FI treatment across cultivars and passivating agents treatments. The available Cd content at maturity was significantly greater in FI than in WDI (P<0.05). In contrast, WDI had higher Cd content on stem, leaf, and kernel organs at maturity than with FI treatment of both cultivars and all of the passivating agents (P<0.05). Generally, the T1 treatment had the maximum available Cd content in the soil layer and highest accumulated Cd content on different aboveground organs, followed by the T2, T3, T4, T5, and T6 treatments considering both cultivars and irrigation regimes. The Cd kernel contents were 0.23-0.24 mg·kg-1 and 0.16-0.21 mg·kg-1 for cultivars Shenliangyou 1813 and Liangyou 6206, respectively, in the T6 treatment. The higher Cd kernel content was generally related to a larger Cd content in the stem organ. For the grain yield, no significant differences were observed among cultivars, irrigation regimes, or passivating agents treatments (P>0.05). Under WDI, the kernel Cd content was still slightly higher than 0.20 mg·kg-1 in the T6 treatment (0.24 mg·kg-1 for cultivar Shenliangyou 1813 and 0.21 mg·kg-1 for cultivar Liangyou 6206); however, there is a predictability potential to produce lower than 0.20 mg·kg-1 kernel content in the T6 treatment if a cultivar with low accumulated capacity is used. Thus, the combined mode of the WDI+T6+cultivar with accumulated low Cd content could be considered an optimized cultivation scheme to obtain no Cd contaminated kernels with high grain yield and water-use efficiency in mildly polluted paddy fields.

The remediation potential and kinetics of cadmium in the green alga Cladophora rupestris.

This study determined the subcellular distribution, chemical forms, and effects of metal homeostasis of excess Cd in Cladophora rupestris. Biosorption data were analyzed with Langmuir and Freundlich adsorption models and kinetic equations. Results showed that C. rupestris can accumulate Cd. Cd mainly localized in the cell wall and debris (42.8-68.2%) of C. rupestris, followed by the soluble fraction (22.1-38.4%) observed in C. rupestris. A large quantity of Cd ions existed as insoluble CdHPO4 complexed with organic acids, Cd(H2PO4)2, Cd-phosphate complexes (FHAC) (43.2-56.0%), and pectate and protein-integrated Cd (FNaCl) (30.8-43.2%). The adsorption data were well fitted by the Freundlich model (R2 = 0.933) and could be described by the pseudo-second-order reaction rate (R2 = 0.997) and Elovich (R2 = 0.972) equations. Related parameters indicated that Cd adsorption by C. rupestris is a heterogeneous diffusion. Cd promoted Ca and Zn uptake by C. rupestris. Cu, Fe, Mn, and Mg adsorption was promoted by low Cd concentrations and inhibited by high Cd concentrations. Results suggested that cell wall sequestration, vacuolar compartmentalization, and chemical morphological transformation are important mechanisms of Cd stress tolerance by C. rupestris. This study suggests that C. rupestris has bioremediation potential of Cd.

Effects of cadmium on bioaccumulation and biochemical stress response in rice (Oryza sativa L.).

This study investigated the effects of various Cd concentrations on the bioaccumulation, antioxidative defense, and stress responses of rice (Oryza sativa L.). The distribution characteristics of Cd in rice were in the following order: roots>stems>grains. The bioconcentration factor values of Cd increased at concentrations lower than 3.00 mg Cd/kg and approximately decreased to a constant value at concentrations higher than 3.00 mg Cd/kg. Rice showed a higher Cd accumulation potential at low Cd concentrations than at high Cd concentrations. The Freundlich isotherm model described well the adsorption isotherms of Cd in rice roots. The biosorption mechanism of rice roots was determined to be cooperative adsorption. The malondialdehyde (MDA) content increased at a concentration range of 0.00-5.00 mg/L, indicating the enhancement of lipid peroxidation. By contrast, the MDA content slightly decreased at concentrations higher than 5.00 mg/L. Peroxidase (POD) activity exhibited active response to oxidative stress at concentrations lower than 5.00 mg/L but was inhibited at concentrations higher than 5.00 mg/L. The response to Cd stress of the N-H, O-H and C-O functional groups in rice shoots was observed via Fourier transform infrared spectroscopy.