Effects of Exogenous Application of Plant Growth Regulators (SNP and GA3) on Phytoextraction by Switchgrass (Panicum virgatum L.) Grown in Lead (Pb) Contaminated Soil

Cadmium biosorption and mechanism investigation using two cadmium-tolerant microorganisms isolated from rhizosphere soil of rice

Microbial remediation of cadmium-contaminated soil offers advantages like environmental friendliness, cost-effectiveness, and simple operation. However, the efficacy of this remediation process relies on obtaining dominant strains and a comprehensive understanding of their Cd adsorption mechanisms. This study identified two Cd-resistant bacteria, Burkholderia sp. 1-22 and Bacillus sp. 6-6, with significant growth-promoting effects from rice rhizosphere soil. The strains showed remarkable Cd resistance up to ∼200 mg/L and alleviated Cd toxicity by regulating pH and facilitating bacterial adsorption of Cd. FTIR analysis showed crucial surface functional groups, like carboxyl and amino groups, on bacteria played significant roles in Cd adsorption. The strains could induce CdCO3 formation via a microbially induced calcium precipitation (MICP) mechanism, confirmed by SEM-EDS, X-ray analysis, and elemental mapping. Pot experiments showed these strains significantly increased organic matter and enzyme activity (e.g., urease, sucrase, peroxidase) in the rhizosphere soil versus the control group. These changes are crucial for restricting Cd mobility. Furthermore, strains 6-6 and 1-22 significantly enhance plant root detoxification of Cd, alleviating toxicity. Notably, increased pH likely plays a vital role in enhancing Cd precipitation and adsorption by strains, converting free Cd into non-bioavailable forms.

Recent advances in phyto-combined remediation of heavy metal pollution in soil

The global industrialization and modernization have witnessed a rapid progress made in agricultural production, along with the issue of soil heavy metal (HM) pollution, which has posed severe threats to soil quality, crop yield, and human health. Phytoremediation, as an alternative to physical and chemical methods, offers a more cost-effective, eco-friendly, and aesthetically appealing means for in-situ remediation. Despite its advantages, traditional phytoremediation faces challenges, including variable soil physicochemical properties, the bioavailability of HMs, and the slow growth and limited biomass of plants used for remediation. This study presents a critical overview of the predominant plant-based HM remediation strategies. It expounds upon the mechanisms of plant absorption, translocation, accumulation, and detoxification of HMs. Moreover, the advancements and practical applications of phyto-combined remediation strategies, such as the addition of exogenous substances, genetic modification of plants, enhancement by rhizosphere microorganisms, and intensification of agricultural technologies, are synthesized. In addition, this paper also emphasizes the economic and practical feasibility of some strategies, proposing solutions to extant challenges in traditional phytoremediation. It advocates for the development of cost-effective, minimally polluting, and biocompatible exogenous substances, along with the careful selection and application of hyperaccumulating plants. We further delineate specific future research avenues, such as refining genetic engineering techniques to avoid adverse impacts on plant growth and the ecosystem, and tailoring phyto-combined strategies to diverse soil types and HM pollutants. These proposed directions aim to enhance the practical application of phytoremediation and its integration into a broader remediation framework, thereby addressing the urgent need for sustainable soil decontamination and protection of ecological and human health.

Unveiling Innovative Approaches to Mitigate Metals/Metalloids Toxicity for Sustainable Agriculture

Due to anthropogenic activities, environmental pollution of heavy metals/metalloids (HMs) has increased and received growing attention in recent decades. Plants growing in HM-contaminated soils have slower growth and development, resulting in lower agricultural yield. Exposure to HMs leads to the generation of free radicals (oxidative stress), which alters plant morpho-physiological and biochemical pathways at the cellular and tissue levels. Plants have evolved complex defense mechanisms to avoid or tolerate the toxic effects of HMs, including HMs absorption and accumulation in cell organelles, immobilization by forming complexes with organic chelates, extraction via numerous transporters, ion channels, signaling cascades, and transcription elements, among others. Nonetheless, these internal defensive mechanisms are insufficient to overcome HMs toxicity. Therefore, unveiling HMs adaptation and tolerance mechanisms is necessary for sustainable agriculture. Recent breakthroughs in cutting-edge approaches such as phytohormone and gasotransmitters application, nanotechnology, omics, and genetic engineering tools have identified molecular regulators linked to HMs tolerance, which may be applied to generate HMs-tolerant future plants. This review summarizes numerous systems that plants have adapted to resist HMs toxicity, such as physiological, biochemical, and molecular responses. Diverse adaptation strategies have also been comprehensively presented to advance plant resilience to HMs toxicity that could enable sustainable agricultural production.

In Situ Remediation Technology for Heavy Metal Contaminated Sediment: A Review

Sediment is an important part of the aquatic ecosystem, which involves material storage and energy exchange. However, heavy metal pollution in sediment is on the increase, becoming an important concern for the world. In this paper, the state-of-art in situ remediation technology for contaminated sediment was elaborated, including water diversion, capping, electrokinetic remediation, chemical amendments, bioremediation and combined remediation. The mechanisms for these techniques to reduce/immobilize heavy metals include physical, electrical, chemical and biological processes. Furthermore, application principle, efficiency and scope, advantages and disadvantages, as well as the latest research progress for each restoration technology, are systematically reviewed. This information will benefit in selecting appropriate and effective remediation techniques for heavy metal-contaminated sediment in specific scenarios.

Strawberry Biostimulation: From Mechanisms of Action to Plant Growth and Fruit Quality

The objective of this review is to present a compilation of the application of various biostimulants in strawberry plants. Strawberry cultivation is of great importance worldwide, and, there is currently no review on this topic in the literature. Plant biostimulation consists of using or applying physical, chemical, or biological stimuli that trigger a response-called induction or elicitation-with a positive effect on crop growth, development, and quality. Biostimulation provides tolerance to biotic and abiotic stress, and more absorption and accumulation of nutrients, favoring the metabolism of the plants. The strawberry is a highly appreciated fruit for its high organoleptic and nutraceutical qualities since it is rich in phenolic compounds, vitamins, and minerals, in addition to being a product with high commercial value. This review aims to present an overview of the information on using different biostimulation techniques in strawberries. The information obtained from publications from 2000-2022 is organized according to the biostimulant's physical, chemical, or biological nature. The biochemical or physiological impact on plant productivity, yield, fruit quality, and postharvest life is described for each class of biostimulant. Information gaps are also pointed out, highlighting the topics in which more significant research effort is necessary.

Evaluation of Chelating Agents Used in Phytoextraction by Switchgrass of Lead Contaminated Soil

Soil lead (Pb) contamination is a recognized environmental and global health problem. Phytoextraction of Pb using switchgrass (Panicum virgatum L.), a second-generation biofuel crop, is typically enhanced by soil chelation. The effectiveness of four different chelating agents, phytic acid (inositol hexaphosphate), citric acid, NTA (nitrilotriacetic acid), and EDTA (ethylenediaminetetraacetic acid) was examined in pot culture. Plants treated with EDTA (1 mM) showed significantly higher shoot Pb concentrations compared to control plants and plants treated with other chelates. Lead-solubility following phytoextraction was examined by soil washing using 0.01 and 0.05 M acetic acid as an extractant solution revealed no significant differences in Pb concentrations in soil among different chelate treatments and control. Furthermore, the effects of different concentrations (1, 2, 5 and 10 mM) of NTA on Pb phytoextraction of switchgrass were examined. Plants receiving 5 mM and 10 mM NTA had significantly higher foliage concentrations of Pb compared to plants treated with lower levels (1 and 2 mM) of NTA. Moreover, the effect of NTA application alone was significantly improved by a combined application of Triton X-100, an alkyl polyglucoside (APG); the Pb concentration in the foliage of switchgrass was more than doubled when treated with NTA combined with APG. The use of NTA combined with APG has great potential in improving phytoextraction efficiencies of switchgrass on Pb-contaminated soils.