Beneficial Microorganisms Improve Agricultural Sustainability under Climatic Extremes

Overview

This MDPI Life review synthesises laboratory, greenhouse, and field evidence on how plant growth-promoting rhizobacteria (PGPB, including Azospirillum, Bradyrhizobium, Pseudomonas, Bacillus, Enterobacter, Burkholderia, Pantoea, Rhizobium, Serratia, Arthrobacter, Microbacterium spp. and others) and plant growth-promoting fungi (PGPF, including arbuscular mycorrhizal fungi Glomus / Funneliformis / Rhizophagus, Trichoderma, Penicillium, Aspergillus spp.) ameliorate the impact of climatic-extreme abiotic stresses on cereal, legume, oilseed, vegetable, and forage crops. The abstract (page 1) groups the stresses into six categories — “drought, salinity, heavy metals, flooding, extreme temperatures, and intense light” — and the body splits “extreme temperatures” into separate high-temperature (Section 5) and low-temperature (Section 6) sections, yielding seven body chapters: drought, salinity, heavy metals, high temperature, low temperature, flooding/oxygen deficit, and intense light. The paper is a narrative review with no independent measurements, no primary data extraction, and no quantitative meta-analysis; tabular entries in Tables 1–3 are microorganism / stress / host-plant pairings catalogued from cited primary studies rather than occurrence values. It is ingested as an out-of-core-scope agronomic-mitigation-context reference following the Appraisal of Functions and Role of Selenium in Heavy Metal Stress Adaptation in Plants and Safety Evaluation of Absorbent Hygiene Pads: A Review on Assessment Framework and Test Methods precedent for methodology / context reviews without primary metal-occurrence data; metals: [], ingredients: [], and products: [] are correct because the paper contributes no measured contamination values to any HMI ingredient, product, or metal page. The heavy-metals section (Section 4, pages 7–8, and Table 2) is potentially useful as a starting point for a future HMI mitigation-lever entry on microbial bioremediation / phytostabilisation / phytoextraction / phyto-volatilisation as a soil-side intervention to reduce heavy-metal uptake into crops, but each specific mechanistic or quantitative claim should be sourced from its underlying primary citation rather than from this tertiary review.

Key numbers

This is a narrative review with no primary measurements. The numerical content consists of (a) the review’s own qualitative framing of heavy-metal toxicity mechanisms, (b) microorganism × heavy-metal pairings catalogued from cited primary studies in Table 2, and (c) crop-yield / stress-impact statistics quoted from cited primary studies in the prose.

Author-stated framing of heavy metals (Section 4, pages 7–8)

• “Heavy metals are generally categorized to belong to the group of metals and metalloids with high atomic density (density greater than 4 g cm⁻³) and mass” (cited to ref [142], page 7).
• “Heavy metals include non-essential plant elements such as lead (Pb), cadmium (Cd), aluminum (Al), chromium (Cr), mercury (Hg), arsenic (As), silver (Ag), and platinum group elements” (cited to refs [143,146]).
• “Some heavy metals, such as copper (Cu), iron (Fe), manganese (Mn), zinc (Zn), nickel (Ni), and molybdenum (Mo), are essential micronutrients … however, their high concentration can cause phytotoxicity” (cited to refs [143,147]).
• “Heavy metal toxicity in plants can cause leaf chlorosis, alter chlorophyll a and b ratios, decrease photosynthesis, inhibit root elongation, increase ROS production and membrane leakage, and change lipid composition through changing inter-cellular concentrations of nutrients” (cited to refs [148,149], page 8).
• Microbe-mediated remediation modes listed: “Microbes play a key role in the remediation of HMs through phyto-stabilization, phyto-extraction, and phyto-volatilization” (cited to refs [131,146]).

Table 2 — Microorganism × heavy-metal pairings in contaminated-site remediation studies, 2010–2020 (page 8)

Microorganism / heavy metal / primary-citation reference, as catalogued by the authors. The review does not report concentration values; it reports which microbe was studied against which metal in which cited primary study.

Microbe-and-heavy-metal context bullets from prose (pages 7–8)

• Most-represented bacterial genera in heavy-metal-contaminated sites listed as Bacillus, Pseudomonas, and Arthrobacter in phyla Firmicutes, Proteobacteria, and Actinobacteria (cited to refs [131,151]).
• Microbial enhancement of phytoremediation attributed to organic-acid production, siderophore production, bio-surfactant production, bio-methylation, and redox processes that “transform heavy metals into soluble and bioavailable forms” (cited to refs [9,150]). Note the directionality: in a phytoextraction context, “bioavailable” means more uptake into plant shoots for harvest-and-disposal; in a food-safety context the same mechanism risks increased contamination of edible crop fractions. The review does not draw this distinction.
• IAA and ACC-deaminase synthesis by PGPB / PGPF cited as the molecular mechanisms enhancing biomass and phytoremediation under heavy-metal exposure (cited to refs [131,150]).
• Co-stress study: Farwell et al. inoculated canola with Pseudomonas putida UW4 under nickel and flood stress and reported increased canola growth and biomass under flooding + heavy-metal stress (cited to ref [250], page 12). Cao et al. reported that flooding “increased enzymatic activity in copper (Cu)-contaminated soil” and that Cu presence is “inversely proportional to soil microbiota (bacteria and fungi)” (cited to ref [239], page 12).

Author-stated crop / yield statistics from cited primary studies (Section 2–3, pages 5–6; not heavy-metals-specific)

• “Drought can reduce yield and cultivation potential (ideal yield) of soybean by up to 70%” (cited to ref [92], page 5).
• “Soils irrigated with saturated water extract with an EC of 4.0 dS m⁻¹ (40 mmol L⁻¹ of NaCl) are considered to be saline and can cause osmotic pressure of 0.2 MPa that leads to a reduction in vegetable yields” (cited to ref [119], page 6).
• These figures are reported here only because they appear in the source’s framing; they are not heavy-metals occurrence values and do not feed any wiki page.

Methods (brief)

Narrative literature review covering predominantly 2012–2022 with select earlier citations back to 2007. The authors did not declare a PRISMA protocol, did not report search platforms / databases / search strings, did not state inclusion or exclusion criteria, and did not perform quantitative meta-analysis or independent data extraction. The structure is a thematic synthesis organised by stress class (drought, salt, heavy metals, high temperature, low temperature, flooding, light). Tables 1–3 catalogue microorganism / stress / host-plant pairings from cited primary studies, listing only the microbe, the stress class, the plant species, and the primary citation — no concentrations, doses, durations, or quantitative response measurements are tabulated. Figures 1–2 are schematic diagrams of abiotic-stress impact pathways and microbe-induced resistance mechanisms, not quantitative data. The review reports no novel laboratory work, no independent re-analysis of primary data, and no occurrence measurements in any food, feed, soil, or environmental matrix.

Implications

• Microbiome: Adjacent. The review’s heavy-metals section (Section 4 + Table 2) and the flood + Cu / Ni co-stress passages (Section 7, page 12) intersect microbiome-and-heavy-metals territory, but in the agronomic / rhizosphere register rather than the human-gut / WikiBiome federation register. Out of scope for Microbiome federation as currently scoped; flag for the future agronomic-microbiome-and-heavy-metals page if one is created.
• Synthesis: No synthesis triggers fire from this ingest. The paper does not contribute primary occurrence values to any ingredient contamination_profile cell.

Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git.