Exploring phytoremediation potential of willow NJU513 for cadmium-contaminated soil with and without epibrassinolide treatment.

There has been a growing concern over soil cadmium (Cd) pollution, underscoring the importance of finding effective remediation strategies. Willow trees have emerged as promising candidates for phytoremediation of Cd-contaminated soils. Nevertheless, the specific potential of a novel willow genotype, NJU513, in remediating Cd-polluted soil remains unexplored. Hence, the primary objectives of this study were twofold: firstly, to ascertain the suitability of the willow genotype NJU513 for remediating Cd-contaminated soil; and secondly, to elevate its remediation efficciency with the application of epibrassinolide (Brs). In the pot-culture experiment without Brs, its leaf and stem Cd concentrations were 203 mg kg-1 and 65.1 mg kg-1, with a bioaccumulation factor (BCF) of 20.8 and 6.68, respectively. In the pot-culture experiment with Brs, the corresponding Cd concentrations were 226 mg kg-1 and 59.2 mg kg-1, with a BCF of 23.1 and 6.06, respectively. In addition, the extracted Cd contents were higher in the Brs treatments (1.11-1.37 mg plant-1) than in the no-Brs treatments (0.78-0.96 mg plant-1) because Brs increased the plant biomass and leaf BCF. The mechanism underlying the Cd accumulation of NJU513 leaves with and without Brs was revealed by a transcriptome analysis. The expression levels of genes related to metal ion binding, channel activity, and transporters in leaves were up-regulated, which contributed to the high Cd accumulation and stress tolerance. Analyses of soil metabolites and bacteria in the presence and absence of Brs spraying on willow leaves indicated that soil organic compounds with carboxyl and amino groups may induce Cd activation and passivation, respectively. This study provides valuable insights for developing woody plant varieties that can be used for remediating Cd-contaminated soil.

Effect of elemental sulfur and gypsum application on the bioavailability and redistribution of cadmium during rice growth.

Recently, concerns over heavy metal contamination of soil have grown. The application of sulfur has been recommended to enhance crop productivity and increase soil cadmium (Cd) immobilization. In this study, a pool experiment was conducted to investigate the effects of two sulfur sources and multiple treatment levels on rice growth and Cd accumulation. The two sulfur forms were elemental sulfur (S0) and gypsum, both of which were applied at 0, 0.15, and 0.30 g S kg-1 soil, for a total of five treatments. The results showed that both S0 and gypsum significantly increased rice biomass compared to the control (CK), and rice yield was increased 2.8-4.8 folds. The effect size was greater for gypsum than S0. The application of S0 reduced the rice grain Cd concentration from 0.61 mg kg-1 (CK) to 0.41-0.46 mg kg-1, while gypsum reduced the Cd concentration to 0.24-0.43 mg kg-1. The lower gypsum application level achieved the greatest reduction in rice grain Cd accumulation. This study further demonstrated that the application of S0 and gypsum led to a decrease in the labile Cd percentage and an increase in the stable Cd percentage. In bulk soil, iron and manganese oxide-bound Cd increased by 6.4-7.3% and 0.7-2.0% for the S0 and gypsum treatments, respectively. In the rhizosphere, residual Cd increased by >0.6%. Furthermore, this study found that sulfur application reduced Cd transfer from root to shoot, and significantly decreased rice grain Cd accumulation. These findings indicate that sulfur application to paddy soils can promote rice productivity and effectively remediate soil Cd contamination, with a greater effect by gypsum than S0.

Effects of simulated Cd deposition on soil Cd availability, microbial response, and crop Cd uptake in the passivation-remediation process of Cd-contaminated purple soil.

Atmospheric deposition of heavy metals such as Cd is a threat to ecosystems and food safety. Our knowledge is still limited about the effectiveness of remediation process for Cd-contaminated agro-soils under atmospheric Cd deposition. In this study, eight soil amendments were used in a Cd-contaminated purple soil to investigate their impacts on soil Cd availability, microbial response, and Cd uptake by mustard and corn plants via simulating the atmospheric Cd deposition under laboratory incubation and greenhouse conditions. Results showed that the simulated atmospheric Cd deposition increased the soil high-risk Cd (HR, exchangeable and carbonate Cd) and decreased soil medium-risk Cd fraction (MR, bound to Fe/Mn oxide and organic Cd), and the largest direct effects on crop Cd uptakes were 0.94 and 0.66 for mustard and corn based on the path-coefficient analysis, respectively. Generally, Cd deposition led to decreasing soil microbial biomass carbon, populations of bacteria, fungi and actinomycetes, and enzyme activities of urease, catalase, sucrase, and acid phosphatase whereas increasing soil microbial biomass nitrogen. Compared with control and lime treatments, an organic-inorganic combined preparation (OCP) appeared to be effective for remediation of the Cd-contaminated purple soil due to its potential to increase the HR-Cd and reduce both MR-Cd and crop Cd uptake, as accompanied by its neutral effects on soil bacterial alpha diversity and community structure. Results also indicated that application of nitrogen fertilizers should be considered for remediation of the Cd-contaminated soils as nitrogen inputs were demonstrated to promote soil health under elevated Cd condition.

[Effect of Nano Zeolite on Chemical Fractions of Cd in Soil and Uptake by Chinese Cabbage at Different Soil pH and Cadmium Levels].

Incubation experiments were carried out to investigate the influence of different nano zeolite(NZ) and ordinary zeolite(OZ) levels(0, 5, 10 and 20 g·kg-1) on the fraction distribution coefficient (FDC) of Cd and soil CEC at different soil pH (4, 5, 6, 7 and 8) when exposed to different cadmium(Cd) levels(1, 5, 10 and 15 mg·kg-1), and pot experiment were carried out to investigate the effects of nano zeolite(NZ) and ordinary zeolite(OZ) on the growth, Cd concentration and Cd accumulation of Chinese cabbage. The results showed that nano zeolite and ordinary zeolite decreased the concentration and FDC of exchangeable Cd (EX-F), and increased the concentration and FDC of carbonate(CAB-F), Fe-Mn oxide(FMO-F), organic matter (OM-F) and residual fraction(RES-F) in incubation experiments. At the end of incubation, the FDC of soil exchangeable Cd decreased from 72.0%-88.0% to 2.4%-10.7%. The decreasing effect of zeolite on the concentration and FDC of exchangeable Cd (EX-F) increased with the increase of zeolite, and the decreasing effect of nano zeolite (NZ) was better than that of ordinary zeolite (OZ). During the culture of 28 d, the concentration of different Cd fractions in soil was in order of EX-F>RES-F>FMO-F>CAB-F>OM-F under different pH conditions. Exchangeable fraction Cd was the dominant fraction of Cd in soil during the whole incubation. Soil CEC had significant negative correlation with soil exchangeable Cd (EX-F) (P<0.01), and significant positive correlation with the concentrations of Fe-Mn oxide(FMO-F) and organic matter (OM-F) in soil(P<0.01). Nano zeolite and ordinary zeolite effectively increased soil CEC, and soil CEC increased with the increase of the pH value of soil in the zeolite treatments. Significant negative correlation was found in soil pH with soil exchangeable Cd (EX-F)(P<0.01). The dry weight of plant tissues in Chinese cabbage increased by 14.3%-131.4% in the presence of nano zeolite(NZ) and ordinary zeolite(OZ), and Cd concentration of shoot and root decreased by 1.0%-75.0% and 3.8%-53.2%, respectively. Higher concentration and accumulation of Cd were observed in XJC3 variety than those in SD 4 variety. Compared with ordinary zeolite (OZ), nano zeolite (NZ) was better in increasing the biomass of Chinese cabbage as well as decreasing accumulation of Cd in Chinese cabbage.