Differential responses to high soil chromium of two arbuscular mycorrhizal fungi communities isolated from Cr-polluted and non-polluted rhizospheres of Ricinus communis

Fungal community determines soil multifunctionality during vegetation restoration in metallic tailing reservoir

Microorganisms are pivotal in sustaining soil functions, yet the specific contributions of bacterial and fungal succession on the functions during vegetation restoration in metallic tailing reservoirs remains elusive. Here, we explored bacterial and fungal succession and their impacts on soil multifunctionality along a ∼50-year vegetation restoration chronosequence in China's largest vanadium titano-magnetite tailing reservoir. We found a significant increase in soil multifunctionality, an index comprising factors pertinent to soil fertility and microbially mediated nutrient cycling, along the chronosequence. Despite increasing heavy metal levels, both bacterial and fungal communities exhibited significant increase in richness and network complexity over time. However, fungi demonstrated a slower succession rate and more consistent composition than bacteria, indicating their relatively higher resilience to environmental changes. Soil multifunctionality was intimately linked to bacterial and fungal richness or complexity. Nevertheless, when scrutinizing both richness and complexity concurrently, the correlations disappeared for bacteria but remained robust for fungi. This persistence reveals the critical role of the fungal community resilience in sustaining soil multifunctionality, particularly through their stable interactions with powerful core taxa. Our findings highlight the importance of fungal succession in enhancing soil multifunctionality during vegetation restoration in metallic tailing reservoirs, and manipulating fungal community may expedite ecological recovery of areas polluted with heavy metals.

Streptomyces N2A, an endophytic actinobacteria that promotes soybean growth and increases yield and seed quality under field conditions

Sustainable agriculture based on the use of soil-beneficial microbes such as plant growth-promoting rhizobacteria (PGPR) and biocontrol agents (BCA) is gaining great consideration to reduce the use of agrochemicals for crop production. With this aim, in this study, a total of 78 actinobacteria were isolated from the rhizosphere and endosphere of soybean roots. Based on in vitro compatibility with Bradyrhizobium japonicum, the ability to produce phytohormones, siderophores, exo-enzymes, antifungal compounds and phosphate solubilization (PGPR traits), two endophytic strains, named N2A and N9, were selected to evaluate their effects on plant growth and development at greenhouse and field conditions. Greenhouse trials showed significantly promoted seedling emergence compared to control and the conventional fungicide treatment. Analysis of growth and development associated parameters at reproductive stages and maturity at greenhouse, but also and most importantly, in field experiments showed significant improvements. Plant biomass, node number, pod number, and consequently yield, were higher in plants previously treated with N2A and co-inoculated with B. japonicum compared to the conventional seed treatment. Furthermore, a significant increase in health status and vigor was observed for seeds harvested from the N2A-treated plants in relation to seeds obtained from the conventional treatment. Thus, we demonstrated that Streptomyces sp. N2A can replace traditional chemical fungicides to protect the seed during germination, allowing good implantation, but also, stimulating the growth and development of soybean crop increasing yield and seed quality at field conditions. Altogether, this supports the potential use of Streptomyces N2A as a PGPR for soybean crop production more efficiently and sustainably.

Effect of iron-loaded sludge biochar amendments on phytoremediation potential of Cr-contaminated soils by Leersia hexandra swartz

In this study, the effect of iron-loaded sludge biochar (ISBC) with different amendment dosages (mass ratio of biochar to soil equal to 0, 0.01, 0.025 and 0.05) on the phytoremediation potential of Leersia hexandra swartz (L. hexandra) to Cr-contaminated soil was investigated. With increasing ISBC dosage from 0 to 0.05, plant height, aerial tissue biomass and root biomass increased from 15.70 cm, 0.152 g pot-1 and 0.058 g pot-1 to 24.33 cm, 0.304 g pot-1 and 0.125 g pot-1, respectively. Simultaneously, the Cr contents in aerial tissues and roots increased from 1039.68 mg kg-1 to 2427.87 mg kg-1 to 1526.57 mg kg-1 and 3242.62 mg kg-1, respectively. Thus, the corresponding bioenrichment factor (BCF), bioaccumulation factor (BAF), total phytoextraction (TPE) and translocation factor (TF) values were also increased from 10.52, 6.20, 0.158 mg pot-1 (aerial tissue)/0.140 mg pot-1 (roots) and 0.428 to 15.15, 9.42, 0.464 mg pot-1 (aerial tissue)/0.405 mg pot-1 (roots) and 0.471, respectively. The significant positive effect of ISBC amendment was primarily attributed to the following three aspects: 1) the root resistance index (RRI), tolerance index (TI) and growth toxicity index (GTI) of L. hexandra to Cr were increased from 100%, 100% and 0%-216.88%, 155.02% and 42.18%, respectively; 2) the bio-available Cr content in the soil was decreased from 1.89 mg L-1 to 1.48 mg L-1, while the corresponding TU (toxicity units) value was declined from 0.303 to 0.217; 3) the activities of urease, sucrase and alkaline phosphatase in soil were increased from 0.186 mg g-1, 1.40 mg g-1 and 0.156 mg g-1 to 0.242 mg g-1, 1.86 mg g-1 and 0.287 mg g-1, respectively. In summary, ISBC amendment was able to significantly improve the phytoremediation of Cr-contaminated soils by L. hexandra.

The Application of Arbuscular Mycorrhizal Fungi as Microbial Biostimulant, Sustainable Approaches in Modern Agriculture

Biostimulant application can be considered an effective, practical, and sustainable nutritional crop supplementation and may lessen the environmental problems related to excessive fertilization. Biostimulants provide beneficial properties to plants by increasing plant metabolism, which promotes crop yield and improves the quality of crops; protecting plants against environmental stresses such as water shortage, soil salinization, and exposure to sub-optimal growth temperatures; and promoting plant growth via higher nutrient uptake. Other important benefits include promoting soil enzymatic and microbial activities, changing the architecture of roots, increasing the solubility and mobility of micronutrients, and enhancing the fertility of the soil, predominantly by nurturing the development of complementary soil microbes. Biostimulants are classified as microbial, such as arbuscular mycorrhizae fungi (AMF), plant-growth-promoting rhizobacteria (PGPR), non-pathogenic fungi, protozoa, and nematodes, or non-microbial, such as seaweed extract, phosphite, humic acid, other inorganic salts, chitin and chitosan derivatives, protein hydrolysates and free amino acids, and complex organic materials. Arbuscular mycorrhizal fungi are among the most prominent microbial biostimulants and have an important role in cultivating better, healthier, and more functional foods in sustainable agriculture. AMF assist plant nutrient and water acquisition; enhance plant stress tolerance against salinity, drought, and heavy metals; and reduce soil erosion. AMF are proven to be a sustainable and environmentally friendly source of crop supplements. The current manuscript gives many examples of the potential of biostimulants for the production of different crops. However, further studies are needed to better understand the effectiveness of different biostimulants in sustainable agriculture. The review focuses on how AMF application can overcome nutrient limitations typical of organic systems by improving nutrient availability, uptake, and assimilation, consequently reducing the gap between organic and conventional yields. The aim of this literature review is to survey the impacts of AMF by presenting case studies and successful paradigms in different crops as well as introducing the main mechanisms of action of the different biostimulant products.

Arbuscular mycorrhizal fungi-induced tolerance to chromium stress in plants

Chromium (Cr) is one of the toxic elements that harms all forms of life, including plants. Industrial discharges and mining largely contribute to Cr release into the soil environment. Excessive Cr pollution in arable land significantly reduces the yield and quality of important agricultural crops. Therefore, remediation of polluted soil is imperative not only for agricultural sustainability but also for food safety. Arbuscular mycorrhizal fungi (AMF) are widespread soil-borne endophytic fungi that form mutualistic relationships with the vast majority of land plants. In mycorrhizal symbiosis, AMF are largely dependent on the host plant-supplied carbohydrates and lipids, in return, AMF aid the host plants in acquiring water and mineral nutrients, especially phosphorus, nitrogen and sulfur from distant soils, and this distinguishing feature of the two-way exchange of resources is a functional requirement for such mutualism and ecosystem services. In addition to supplying nutrients and water to plants, the AMF symbiosis enhances plant resilience to biotic and abiotic stresses including Cr stress. Studies have revealed vital physiological and molecular mechanisms by which AMF alleviate Cr phytotoxicity and aid plants in nutrient acquisition under Cr stress. Notably, plant Cr tolerance is enhanced by both the direct effects of AMF on Cr stabilization and transformation, and the indirect effects of AMF symbiosis on plant nutrient uptake and physiological regulation. In this article, we summarized the research progress on AMF and associated mechanisms of Cr tolerance in plants. In addition, we reviewed the present understanding of AMF-assisted Cr remediation. Since AMF symbiosis can enhance plant resilience to Cr pollution, AMF may have promising prospects in agricultural production, bioremediation, and ecological restoration in Cr-polluted soils.

Arbuscular Mycorrhizal Fungi Are an Influential Factor in Improving the Phytoremediation of Arsenic, Cadmium, Lead, and Chromium

The increasing expansion of mines, factories, and agricultural lands has caused many changes and pollution in soils and water of several parts of the world. In recent years, metal(loid)s are one of the most dangerous environmental pollutants, which directly and indirectly enters the food cycle of humans and animals, resulting in irreparable damage to their health and even causing their death. One of the most important missions of ecologists and environmental scientists is to find suitable solutions to reduce metal(loid)s pollution and prevent their spread and penetration in soil and groundwater. In recent years, phytoremediation was considered a cheap and effective solution to reducing metal(loid)s pollution in soil and water. Additionally, the effect of soil microorganisms on increasing phytoremediation was given special attention; therefore, this study attempted to investigate the role of arbuscular mycorrhizal fungus in the phytoremediation system and in reducing contamination by some metal(loid)s in order to put a straightforward path in front of other researchers.

Impact of increasing chromium (VI) concentrations on growth, phosphorus and chromium uptake of maize plants associated to the mycorrhizal fungus Rhizophagus irregularis MUCL 41833

Arbuscular mycorhizal fungi (AMF) associated to plants may represent a promising phyto-remediation avenue due to the widely documented role of these fungi in alleviation of numerous abiotic (e.g. heavy metals) stresses. In the present work, it was the objective to study the dynamics of inorganic phosphorus (Pi) and chromium(VI) (Cr(VI)) and total Cr uptake by the plant-AMF associates Zea mays + R. irregularis MUCL 41833, under increasing (i.e. 0, 0.1, 1 and 10 mg L⁻¹) concentrations of Cr(VI). The plant-AMF associates were grown in a circulatory semi-hydroponic cultivation system under greenhouse conditions. We demonstrated that Cr(VI) had an hormesis effect on root colonization of maize. Indeed, at 0.1 and 1 mg L⁻¹ Cr(VI), root colonization was increased by approximately 55% as compared to the control (i.e. in absence of Cr(VI) in the solution), while no difference was noticed at 10 mg L⁻¹ Cr(VI) (P ≤ 0.05). However, this did not result in an increased uptake of Pi by the AMF-colonized plants in presence of 0.1 mg L⁻¹ Cr(VI) as compared to the AMF control in absence of Cr(VI) (P ≤ 0.05). Conversely, the presence of 1 mg L⁻¹ Cr(VI) stimulated the Pi uptake by non-mycorrhizal plants, which absorbed 17% more Pi than their mycorrhizal counterparts (P ≤ 0.05). In addition, the non-mycorrhizal plants absorbed, in average, 8% more Cr(VI) than the mycorrhizal plants. Overall, our results prompt the hypothesis that in presence of AMF, the regulation of uptake of Cr(VI) and Pi by plant roots is done mostly by the fungus rather than the root cells. This regulated uptake of roots associated to AMF would indicate that the symbiosis could benefit the plants by providing a stable Pi uptake in a Cr(VI) polluted environment.

An insight into the current oil spills and on-site bioremediation approaches to contaminated sites in Nigeria

Land oil spills in Nigeria have a long history of contaminating the soil, groundwater, vegetation, and streams with spill extension being the primary of numerous ordeals. These have left the host communities of oil fields and pipelines in crucial need of soil rehabilitation. Thus, this review provides insights into the current state of land oil spills and the effectiveness of on-site remediation approaches across communities. A total of 44 incidents of land oil spills of ≥ 500 bbl, amounting to 53,631 bbl between 2011 and 2019, was recorded by the Shell Petroleum Development Company, which primarily attributed to 83% of the total sabotage. Over 73% of the 53,631 bbl spills were unrecovered from the spill areas, which had deleterious impacts on farmlands, fishponds, rivers, and residential areas. Remediation by enhanced natural attenuation (RENA) is a feasible technique for restoring petroleum hydrocarbon-contaminated sites, but it might be ineffective when limited to tiling, windrows, and fertilizer applications due to the presence of non-biodegradable residues and contaminants beyond the aeration depth. However, bioremediation techniques ranging from non-supplemented in-situ and fertilizer supplemented in-situ to mixed in-situ and ex-situ bio-cells supplemented RENA are feasible approaches for spill sites. However, challenging limitations with regard to RENA application failures in the region include delayed responses to spill emergency, large amounts of un-recovered spilled oil, and un-implemented legislative guidelines for spill cleanup. Nevertheless, the temperature, moisture, nutrient, oxygen, and pH of the soil are essential parameters to be considered when implementing a landfarming remediation approach.