Root chemistry and microbe interactions contribute to metal(loid) tolerance of an aromatic plant - Vetiver grass

Effects of naturally aged microplastics on arsenic and cadmium accumulation in lettuce: Insights into rhizosphere microecology

Naturally aged microplastics (NAMPs) are commonly found in farmland soils contaminated with heavy metals (HMs), such as arsenic (As) and cadmium (Cd); yet their combined effects on soil-plant ecosystems remain poorly understood. In this study, we investigated the toxic effects of NAMPs and As-Cd on lettuce, considering the influence of earthworm activity, and examined changes in As-Cd bioavailability in the rhizosphere. Four experimental systems were established: soil-only, soil-lettuce, soil-earthworms, and soil-lettuce-earthworms systems, with four NAMPs concentrations (0, 0.1, 0.5, 1 %). Our results showed that exposure to 0.1 % NAMPs reduced As accumulation in lettuce shoots (0.17-0.25 mg kg-1) and roots (1.13-1.72 mg kg-1), while increasing biomass and enhancing root growth by alleviating toxicity. In contrast, the combined stress of higher NAMPs concentration (0.5 %/1 %) and As-Cd caused a 28.4-58.4 % reduction in root activity, which stimulated low-molecular-weight organic acid (LMWOA) secretion in the rhizosphere, increasing the bioavailability of As and Cd and enhancing their absorption by lettuce. Partial least squares path modeling (PLS-PM) revealed that co-exposure altered LMWOA content, soil enzyme activity, and microbial community stability in the rhizosphere, ultimately influencing the bioavailability and uptake of As and Cd by lettuce.

Synergistic effects of tree-herb intercropping on the phytoremediation efficiency of cadmium and lead contaminated soil

Tree-herb intercropping has emerged as an effective strategy for the remediation of soil contamination. In this study, the effects of intercropping willow with herbaceous plants Lolium perenne L., Iris lactea Pall. and Bidens pilosa L. were investigated on the phytoremediation of Cd- and Pb-contaminated soil. After a 90-day of cultivation, the results showed that intercropping stimulated the phytoremediation efficiency through increased metal accumulation in plants. Intercropping caused a significant (p < 0.05) increase in willow biomass ranging from 48.07 % to 95.58 % by promoting photosynthesis activities and antioxidant responses. Metal contents in willow leaves and roots were also observably (p < 0.05) enhanced, indicating a beneficial effect in tree-herb intercropping systems. The biomass and metal accumulation of I. lactea Pall. and B. pilosa L. decreased due to competitive interactions with willow in the intercropping treatments. However, intercropping with willow (p < 0.05) significantly increased the Pb contents of L. perenne L. Intercropping improved the absorption of bioavailable fractions of Cd and Pb by willow and herbs in comparison to the monoculture. The decrease in soil Cd contents was partly due to the chemical changes induced by root exudates, which enhanced the transfer of Cd from the soil to the plants. Willow showed a tendency for Cd accumulation, whereas herbs exhibited Pb accumulation, reflecting the complementarity of metal accumulation in tree-herb intercropping patterns. Intercropping willow with B. pilosa L. was found to be an effective method for the remediation of Cd-contaminated soil, whereas the combination of willow with L. perenne L. proved suitable for the Pb-contaminated soil. These findings might support the potential of tree-herb intercropping as an effective strategy for enhancing the phytoremediation of contaminated soils.

Earthworm mucus contributes significantly to the accumulation of soil cadmium in tomato seedlings

Whether earthworm mucus affects Cd transport behavior in soil-plant systems remains uncertain. Consequently, this study thoroughly assessed the impacts of earthworm mucus on plant growth and physiological responses, plant Cd accumulation, translocation, and distribution, as well as soil characteristics and Cd fractionation in a soil-plant (tomato seedling) system. Results demonstrated that the earthworm inoculation considerably enhanced plant Cd uptake and decreased plant Cd translocation, the effects of which were appreciably less significant than those of the earthworm mucus. This suggested that earthworm mucus may play a crucial role in the way earthworms influence plant Cd uptake and translocation. Moreover, the artificial mucus, which contained identical inorganic nitrogen contents to those in earthworm mucus, had no significant effect on plant Cd accumulation or translocation, implying that components other than inorganic nitrogen in the earthworm mucus may have contributed significantly to the overall effects of the mucus. Compared with the control, the earthworm mucus most substantially increased the root Cd content, the Cd accumulation amount of root and whole plant, and root Cd BCF by 93.7 %, 221.3 %, 72.2 %, and 93.7 %, respectively, while notably reducing the Cd TF by 48.2 %, which may be ascribed to the earthworm mucus's significant impacts on tomato seedling growth and physiological indicators, its considerable influences on the subcellular components and chemical species of root Cd, and its substantial effects on the soil characteristics and soil Cd fractionation, as revealed by correlation analysis. Redundancy analysis further suggested that the most prominent impacts of earthworm mucus may have been due to its considerable reduction of soil pH, improvement of soil DOC content, and enhancement of the exchangeable Cd fraction in soil. This work may help better understand how earthworm mucus influences the transport behavior of metals in soil-plant systems.

Cadmium induced changes in rhizosphere microecology to enhance Cd intake by Ligusticum sinense cv. Chuanxiong

As the most famous and widely used traditional Chinese medicine (TCM), Ligusticum sinense cv. Chuanxiong (L. Chuaniong) has been affected by cadmium (Cd) exceeding with high ability of Cd accumulation. There is relatively little research on Cd absorption and storage process in L. Chuanxiong, which is an important reason for the poor remediation efficiency. Hence, this study takes L. Chuanxiong as the point of penetration to explore how L. Chuanxiong affects rhizobacteria through root exudates to alter soil Cd intake, as well as to explore the migration and storage of Cd in its body with 0.10 (T0), 5.00 (T5), 10.00 (T10) mg/kg Cd contaminations. The results showed that the relative abundance of amino acids and phospholipids secreted from L. Chuanxiong root noticeably increased with increasing Cd levels, which directly activated soil Cd or extremely significantly (P < 0.01) recruited bacteria such as Bacillus, Arthrobacter to indirectly increase Cd availability. Under the interaction of root exudates and rhizobacteria, Cd bioavailability increased by 80.00% in rhizosphere soil and Cd accumulation in L. Chuanxiong increased 5.44-6.65 mg/kg. Cd subcellular distribution analysis demonstrated that Cd was mainly stored in the root (10-fold more than in the leaf), whose Cd content was cytoderm>cytoplasm>organelle in tissues. The sequential extraction results found that non-soluble phosphate and protein-chelated Cd dominated (85.00-90.00%) in the cell, while Cd cheated with alcohol soluble protein, amino acid salts, water-soluble organic acid in cell was minimal (5.50%). The phenomenon indicated that L. Chuanxiong fixed Cd in root (the medical part) with low translocation ability. This study can provide theoretical support for the high-quality production of L. Chuanxiong and other root medical plant in heavy metal influenced sites.