Escalating anthropogenic activities have caused heavy metal contamination in the environmental matrices. Due to their recalcitrant and toxic nature, their occurrence in high titers in the environment can threaten survival of biotic components. To take the edge off, remediation of metal-contaminated sites by phytoremediators that exhibit a potential to withstand heavy metal stress and quench harmful metals is considered an eco-sustainable approach. Despite the enormous potential, phytoremediation technique suffers a setback owing to high metal concentrations, occurrence of multiple pollutants, low plant biomass, and soil physicochemical status that affect plants at cellular and molecular levels, inducing morphological, physiological, and genetic alterations. Nevertheless, augmentation of soil with microorganisms can alleviate the challenge. A positive nexus between microbes, particularly plant growth-promoting microorganisms (PGPMs), and phytoremediators can prevent phytotoxicity and augment phytoremediation by employing strategies such as production of secondary metabolites, solubilization of phosphate, and synthesis of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase and phytohormones. Microbes can mediate tolerance in plants by fortifying their antioxidant machinery, which maintains redox homeostasis and alleviates metal-induced oxidative damage in the plants. Associated microbes can also activate stress-responsive genes in plants and abridge metal-induced toxic effects. An in-depth exploration of the mechanisms employed by plant-associated microbes to trigger tolerance in phytoremediators is crucial for improving their phytoremediation potential and real-world applications. The present article attempts to comprehensively review these mechanisms that eventually facilitate the development of improved/new technology for soil ecosystem restoration.

Soil metal pollution is a global issue due to its toxic nature affecting ecosystems and human health. This has become a concern since metals are non-biodegradable and toxic. Most of the reclamation methods currently used for soils rely on the use of physical and chemical means, which tend to be very expensive and result in secondary environmental damage. However, microbe-aided phytoremediation is gaining attention as it is an ecofriendly, affordable, and technically advanced method to restore the ecosystem. It is essential to understand the complex interaction between plants and microbes. The primary function of plant growth-promoting bacteria (PGPB) is to stimulate plant development, aid in metal elimination, and reduce their bioavailability in the soil. These microbes regulate phytohormones, stimulate processes such as phytoextraction and phyto-stabilization, and improve the uptake of essential nutrients, such as nitrogen and phosphorus. PGPBs secrete a range of enzymes and chemicals, fix nitrogen, solubilize minerals, increase the bioavailability of nutrients under diverse biological environments with high salinities, excessive metal-contaminated soil, and organic pollutants, increase the soil fertility and help in the reclamation of agriculture and regenerate the native flora. The integration of CRISPR-Cas9 gene-editing technology with microbialaided phytoremediation and the use of genetically modified microbes with nanomaterials further enhance the efficacy of the approaches in polluted environments for sustainable restoration of the soil.

Most improved strategies for phytoextraction do not achieve a synergistic enhancement of chromium (Cr) accumulation capacity and biomass. This study investigated the impacts of co-addition of garbage enzyme (GE) and microelectrolytic iron-carbon filler (MF) on soil physicochemical properties, as well as form and uptake of Cr during aging and phytoextraction process. The response of rhizosphere microbial community to co-addition and its role in enhancing the remediation performance of ryegrass was further analyzed. Co-addition of GE and MF during the 12-day aging process resulted in an increase of nutrients, a shift from an oxidising to a reducing soil environment, a decrease of Cr(VI) content, and an enhancement of soil microbial community diversity and richness, creating a suitable environment for subsequent phytoextraction. During the 40-day phytoextraction process, co-addition played a crucial role in facilitating the establishment of a complex, efficient and interdependent ecological network among soil microorganisms and contributed to the evolution of microbial community composition and functional pathways. An increase in the relative abundance of Trichococcus, Azospirillum and g_norank_f_JG30-KF-CM45 elevated soil nutrient levels, while a decrease in the relative abundance of TM7a and Brucella reduced pathogen harbouring. Meanwhile, co-addition increased the relative abundance of Bacillus, Arthrobacter and Exiguobacterium, attenuated Cr phytotoxicity and improved soil biochemical activity. These markedly diminished oxidative damage and improved ryegrass growth by reducing malondialdehyde accumulation. In addition, regular additions of GE and the increase in relative abundance of norank_fnorank_o_Microtrichales led to rhizosphere acidification, which inhibited short-term Cr immobilization and contributed to a notable increase in phytoextraction efficiency. This study presents a strategy to enhance phytoremediation efficiency and soil quality during phytoextraction of Cr-contaminated soils.

This study investigated the enhancing effects of soil treatment with ethylene diamine tetraacetic acid (EDTA) and oxalic acid (OA) on the remediation of Cr(VI) contaminated soil by Datura stramonium L. A greenhouse pot experiment was conducted, where Cr(VI) contaminated soil was treated with 100 mg/kg Cr(VI) and varying concentrations of EDTA (5 and 10 mmol/kg) and OA (5 and 10 mmol/kg). The effects of these soil treatments on biomass, chlorophyll content, antioxidant enzyme activities, and Cr(VI) enrichment and translocation efficiency of D. stramonium were evaluated. The results showed that added OA to soil significantly increased the biomass and chlorophyll content of D. stramonium. The addition of 10 mmol/kg of OA to soil increased the plant biomass by 67.16 % and chlorophyll b content by 40.01 %. In addition, OA soil treatment significantly enhanced the activities of superoxide dismutase (SOD) by 6.36 %, peroxidase (POD) by 163.13 %, catalase (CAT) by 36.92 %, and ascorbate peroxidase (APX) by 32.12 %, which effectively alleviated the oxidative stress induced by Cr(VI). In contrast, soil treatment with a high concentration of EDTA (10 mmol/kg) significantly reduced plant biomass and chlorophyll content, although it increased the biological concentration factor (BCF) of the stem and leaf, as well as the translocation factor (TF). In conclusion, appropriate amounts of EDTA and OA added to soil can enhance the phytoremediation efficiency of D. stramonium grown in Cr(VI) contaminated soil, with OA added to soil being more effective than addition of EDTA. This study revealed the potential mechanisms of chelating agents EDTA and OA in enhancing the phytoremediation of Cr(VI) contaminated soil by D. stramonium, providing a scientific basis for further optimization of phytoremediation techniques.

In this study, the phytoremediation efficiency of Arabidopsis halleri L. in response to mechanical injury were compared between those irrigated with magnetized water and those irrigated with normal water. Under normal irrigation treatment, wounding stress increased malondialdehyde (MDA) concentrations and hydrogen peroxide (H2O2) levels in A. halleri leaves significantly, by 46.7-86.1% and 39.4-77.4%, respectively, relative to those in the intact tissues. In addition, wounding stresses decreased the content of Cd in leaves by 26.8-52.2%, relative to the control, indicating that oxidative damage in plant tissues was induced by mechanical injury, rather than Cd accumulation. There were no significant differences in MDA and H2O2 between A. halleri irrigated with magnetized water and with normal water under wounding conditions; however, the activities of catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) in the leaves of plants treated with magnetized water were significantly increased by 25.1-56.7%, 47.3-183.6%, and 44.2-109.4%, respectively. Notably, under the magnetic field, the phytoremediation effect of 30% wounded A. halleri nearly returned to normal levels. We find that irrigation with magnetized water is an economical pathway to improve the tolerance of A. halleri to inevitable mechanical injury and may recover its phytoremediation effect.

Rapid industrialization and extensive agricultural practices are the major causes of soil heavy metal contamination, which needs urgent attention to safeguard the soils from contamination. However, the phytotoxic effects of excessive metals in plants are the primary obstacle to efficient phytoextraction. The present study evaluated the effects of hesperidin (HSP) on metals (Cu, Cd, Cr, Zn) phytoextraction by hyperaccumulator (Celosia argentea L.) plants. For this purpose, HSP, a flavonoid compound with strong antioxidant potential to assist metal phytoextraction was used under metal stress in plants. Celosia argentea plants suffered significant (P <= 0.001) oxidative damage due to the colossal accumulation of metals (Cu, Cd, Cr, Zn). However, HSP supplementation notably (P <= 0.001) abated ROS generation (O2 center dot-, center dot OH, H2O2), lipoxygenase activity, methylglyoxal production, and relative membrane permeability that clearly indicated HSP-mediated decline in oxidative injury in plants. Exogenous HSP improved (P <= 0.001) the production of non -protein thiol, phytochelatins, osmolytes, and antioxidant compounds. Further, HSP enhanced (P <= 0.001) H2S and NO endogenous production, which might have improved the GSH: GSSG ratio. Consequently, HSP-treated C. argentea plants had higher biomass alongside elevated metal accumulation mirrored as profound modifications in translocation factor (TF), bioaccumulation coefficient (BAC), and bioconcentration factor (BCF). In this context, HSP significantly enhanced TF of Cr (P <= 0.001), Cd (P <= 0.001), and Zn (P <= 0.01), while BAC of Cr (P <= 0.001), Cd (P <= 0.001), and Zn (P <= 0.001). Further, BCF was significant (P <= 0.05) only in plants grown under Cr-spiked soil. Overall, HSP has the potential for phytoremediation of metals by C. argentea, which might be a suitable strategy for metal-polluted soils.