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Arbuscular mycorrhizal fungi (AMF) transfer plant photosynthate underground which can stimulate soil microbial growth. In this study, we examined whether there was a potential link between carbon (C) release from an AMF and phosphorus (P) availability via a phosphatesolubilizing bacterium (PSB). We investigated the outcome of the interaction between the AMF and the PSB by conducting a microcosm and two Petri plate experiments. An in vitro culture experiment was also conducted to determine the direct impact of AMF hyphal exudates on growth of the PSB. The AMF released substantial C to the environment, triggering PSB growth and activity. In return, the PSB enhanced mineralization of organic P, increasing P availability for the AMF. When soil available P was low, the PSB competed with the AMF for P, and its activity was not stimulated by the fungus. When additional P was added to increase soil available P, the PSB enhanced AMF hyphal growth, and PSB activity was also stimulated by the fungus. Our results suggest that an AMF and a free-living PSB interacted to the benefit of each other by providing the C or P that the other microorganism required, but these interactions depended upon background P availability.

Arbuscular mycorrhizal fungi form symbiotic associations with most land plants and deliver mineral nutrients, in particular phosphate, to the host. Therefore, understanding the mechanisms of phosphate acquisition and delivery in the fungi is critical for full appreciation of the mutualism in this association. Here, we provide updates on physical, chemical, and biological strategies of the fungi for phosphate acquisition, including interactions with phosphate-solubilizing bacteria, and those on the regulatory mechanisms of phosphate homeostasis based on resurveys of published genome sequences and a transcriptome with reference to the latest findings in a model fungus. For the mechanisms underlying phosphate translocation and export to the host, which are major research frontiers in this field, not only recent advances but also testable hypotheses are proposed. Lastly, we briefly discuss applicability of the latest tools to gene silencing in the fungi, which will be breakthrough techniques for comprehensive understanding of the molecular basis of fungal phosphate metabolism.

Background Excessive application of chemical fertilizer has exerted a great threat to soil quality and the environment. The inoculation of plants with plant-growth-promoting rhizobacteria (PGPR) has emerged as a great prospect for ecosystem recovery. The aim of this work to isolate PGPRs and highlights the effect of bacterial inoculants on available N/P/K content in soil and on the growth of wheat under conditions of reduced fertilizer application. Results Thirty-nine PGPRs were isolated and tested for their growth-promoting potential. Thirteen isolates had nitrogen fixation ability, of which N9 ( Azotobacter chroococcum ) had the highest acetylene reduction activity of 156.26 nmol/gh. Eleven isolates had efficient phosphate solubilizing ability, of which P5 ( Klebsiella variicola ) released the most available phosphorus in liquid medium (231.68 mg/L). Fifteen isolates had efficient potassium solubilizing ability, of which K13 ( Rhizobium larrymoorei ) released the most available potassium in liquid medium (224.66 mg/L). In culture medium supplemented with tryptophan, P9 ( Klebsiella pneumoniae ) produced the greatest amount of IAA. Inoculation with the bacterial combination K14 + 176 + P9 + N8 + P5 increased the alkali-hydrolysed nitrogen, available phosphorus and available potassium in the soil by 49.46, 99.51 and 19.38%, respectively, and enhanced the N, P, and K content of wheat by 97.7, 96.4 and 42.1%, respectively. Moreover, reducing fertilizer application by 25% did not decrease the available nitrogen, phosphorus, and potassium in the soil and N/P/K content, plant height, and dry weight of wheat. Conclusions The bacterial combination K14 + 176 + P9 + N8 + P5 is superior candidates for biofertilizers that may reduce chemical fertilizer application without influencing the normal growth of wheat.

Phosphorus is one of the main nutrients necessary for plant growth and development. Phosphorus-dissolving microorganisms may convert insoluble phosphorus in soil into available phosphorus that plants can easily absorb and utilize. In this study, four phosphorus-solubilizing fungi (L3, L4, L5, and L12) were isolated from the rhizosphere soil of a poplar plantation in Dongtai, Jiangsu Province, China. Phylogenetic analysis based on the internal transcribed spacer (ITS) and large subunit (LSU) of the ribosomal DNA sequences showed that the ITS and 28S sequences of isolates were the most similar to those of Mortierella. Morphological observation showed that most colonies grew in concentric circles and produced spores under different culture conditions. These results and further microscopic observations showed that these isolated fungi belonged to the genus Mortierella. Pikovskaya (PKO) medium, in which tricalcium phosphate was the sole phosphorus source, was used to screen strain L4 with the best phosphorus-solubilizing effect for further study. When the carbon source was glucose, the nitrogen source was ammonium chloride, the pH was 5, and the available phosphorus content was the highest. By exploring the possible mechanism of phosphorus release by phosphorus-solubilizing fungi, it was found that strain L4 produces several organic acids, such as oxalic acid, lactic acid, acetic acid, succinic acid, tartaric acid, malic acid, and citric acid. At 24 h, the alkaline phosphatase and acid phosphatase activities reached 154.72 mol/(L·h) and 120.99 mol/(L·h), respectively.

Phosphorus (P) deficiency remains a critical factor limiting crop productivity, particularly in tropical soils where most phosphorus occurs in insoluble complexes with iron (Fe³⁺) and calcium (Ca²⁺) ions. This study aimed to isolate, characterize, and evaluate the phosphate-solubilizing capacity of rhizospheric bacteria associated with Pterocarpus indicus. Soil samples were analyzed for moisture content, bacterial abundance, and phosphate-solubilizing bacteria (PSB) diversity, followed by the isolation of PSB on selective media. Each isolate was characterized morphologically and microscopically, and its phosphate-solubilizing ability was quantified using the solubilization index (SI) on Pikovskaya agar. The results showed that soil moisture strongly influenced bacterial abundance, with the highest PSB populations recorded in samples A1 (41 ± 2.16 × 10⁵ CFU g⁻¹ at 65.84% moisture) and A3 (41 ± 2.83 × 10⁵ CFU g⁻¹ at 58.74%). In contrast, the lowest population was observed in sample A2 (15 × 10⁵ CFU g⁻¹ at 46.84%), confirming that moderate soil moisture (58–65%) supports optimal PSB growth. Ten distinct PSB isolates (PSB-L1 to PSB-L10) were successfully purified and exhibited wide phenotypic diversity, including bacillus- and coccus-shaped forms with both Gram-positive and Gram-negative reactions. Phosphate-solubilization indices ranged from 0.80 to 4.00, with PSB-L3 and PSB-L8 showing the highest solubilization capacity. These findings demonstrate that native PSB associated with P. indicus possess strong phosphate-solubilizing potential and represent promising candidates for the development of locally adapted biofertilizers aimed at enhancing soil phosphorus availability and supporting sustainable crop production.

Phosphorus (P) availability is usually low in soils around the globe. Most soils have a deficiency of available P; if they are not fertilized, they will not be able to satisfy the P requirement of plants. P fertilization is generally recommended to manage soil P deficiency; however, the low efficacy of P fertilizers in acidic and in calcareous soils restricts P availability. Moreover, the overuse of P fertilizers is a cause of significant environmental concerns. However, the use of arbuscular mycorrhizal fungi (AMF), phosphate–solubilizing bacteria (PSB), and the addition of silicon (Si) are effective and economical ways to improve the availability and efficacy of P. In this review the contributions of Si, PSB, and AMF in improving the P availability is discussed. Based on what is known about them, the combined strategy of using Si along with AMF and PSB may be highly useful in improving the P availability and as a result, its uptake by plants compared to using either of them alone. A better understanding how the two microorganism groups and Si interact is crucial to preserving soil fertility and improving the economic and environmental sustainability of crop production in P deficient soils. This review summarizes and discusses the current knowledge concerning the interactions among AMF, PSB, and Si in enhancing P availability and its uptake by plants in sustainable agriculture.

Phosphorus (P) is a vital element in biological molecules, and one of the main limiting elements for biomass production as plant-available P represents only a small fraction of total soil P. Increasing global food demand and modern agricultural consumption of P fertilizers could lead to excessive inputs of inorganic P in intensively managed croplands, consequently rising P losses and ongoing eutrophication of surface waters. Despite phosphate solubilizing microorganisms (PSMs) are widely accepted as eco-friendly P fertilizers for increasing agricultural productivity, a comprehensive and deeper understanding of the role of PSMs in P geochemical processes for managing P deficiency has received inadequate attention. In this review, we summarize the basic P forms and their geochemical and biological cycles in soil systems, how PSMs mediate soil P biogeochemical cycles, and the metabolic and enzymatic mechanisms behind these processes. We also highlight the important roles of PSMs in the biogeochemical P cycle and provide perspectives on several environmental issues to prioritize in future PSM applications.

The Ecuadorian floriculture sector is currently facing challenges due to the decline in soil nutritional content and productivity. This situation, coupled with nitrogen (N) losses and poor soil phosphorus (P) assimilation, has led to reduced yields in ornamental species such as lily of the Incas (Alstroemeria aurantiaca), resulting in significant economic losses. Various alternatives were evaluated to address these issues. A Randomized Complete Block Design (RCBD) was employed using a two-factor scheme, including the A×B interaction and the intercept. The experimental conditions consisted of microbial applications at doses of 1, 2, and 3 L/ha, applied directly to the soil as a supplementary nutrient treatment. Treatment T2 (2 L/ha), which comprised a microbial consortium, exhibited the best performance. Total production costs were estimated at 3,440 USD per hectare, with an economic efficiency of 2,560 USD, which was rated as satisfactory. El sector florícola ecuatoriano atraviesa dificultades debido a la disminución del contenido nutricional y productividad del suelo, esto unido a pérdidas de N y poca asimilación de P del suelo hace que disminuyan los rendimientos de especies ornamentales como astromelia (Alstroemeria aurantiaca) que provocan grandes pérdidas económicas. Se evaluaron alternativas para solucionar estas problemáticas. Se empleó un DBCA con esquema de dos factores que incluye la interacción A×B y el intercepto. Las condiciones experimentales fueron: 1, 2, 3 L/ha, de microorganismos, aplicados en directamente al suelo por aplicación suplementaria de nutrientes. El tratamiento T2 (2 L/ha), fue el que mejor se comportó, el mismo comprende una mezcla de microorganismos. Los gastos completos de producción se estimaron en 3 440 USD por hectárea. Y una eficiencia económica de 2 560 USD, estimado de satisfactoria.

Introduction of quinoa (Chenopodium quinoa willd.), a gluten-free nutritious pseudo-cereal, outside its traditional growing areas exposed it to seedling damping-off. Here, we isolated eleven phosphate-solubilizing bacteria from the quinoa rhizosphere and assessed their effect on germination and seedlings growth. All isolates solubilized phosphate, produced indole3-acetic acid, hydrocyanic acid, siderophores, and ammonia. Genotypic analysis revealed that our strains are related to the genus of Bacillus, Pseudomonas, and Enterobacter. Strains Enterobacter asburiae (QD14, QE4, QE6, and QE16), Enterobacter sp. QE3, and Enterobacter hormaechei QE7 withstood 1.5 mg·L−1 of cadmium sulfate, 0.5 mg·mL−1 of nickel nitrate, and 1 mg·mL−1 of copper sulfate. Moreover, all strains solubilized zinc from ZnO; P. Stutzeri QD1 and E. asburiae QD14 did not solubilize Zn3(PO4)2 and CO3Zn, whereas CO3Zn was not solubilized by E. asburiae QE16. Bacillus atrophaeus S8 tolerated 11% NaCl. P. frederiksbergensis S6 and Pseudomonas sp. S7 induced biofilm formation. Anti-fusarium activity was demonstrated for E.asburiae QE16, P. stutzeri QD1, P. frederiksbergensis S6, Pseudomonas sp. S7, and B. atrophaeus S8. Lastly, inoculation of quinoa seeds with B. atrophaeus S8 and E. asburiae QB1 induced the best germination rate and seedling growth, suggesting their potential use as inoculants for salty and heavy metal or zinc contaminated soils.

Phosphorus is an essential nutrient for all life on earth and has a major impact on plant growth and crop yield. The forms of phosphorus that can be directly absorbed and utilized by plants are mainly HPO42− and H2PO4−, which are known as usable phosphorus. At present, the total phosphorus content of soils worldwide is 400–1000 mg/kg, of which only 1.00–2.50% is plant-available, which seriously affects the growth of plants and the development of agriculture, resulting in a high level of total phosphorus in soils and a scarcity of available phosphorus. Traditional methods of applying phosphorus fertilizer cannot address phosphorus deficiency problems; they harm the environment and the ore material is a nonrenewable natural resource. Therefore, it is imperative to find alternative environmentally compatible and economically viable strategies to address phosphorus scarcity. Phosphorus-solubilizing bacteria (PSB) can convert insoluble phosphorus in the soil into usable phosphorus that can be directly absorbed by plants, thus improving the uptake and utilization of phosphorus by plants. However, there is no clear and systematic report on the mechanism of action of PSB. Therefore, this paper summarizes the discovery process, species, and distribution of PSB, focusing on the physiological mechanisms outlining the processes of acidolysis, enzymolysis, chelation and complexation reactions of PSB. The related genes regulating PSB acidolysis and enzymatic action as well as genes related to phosphate transport and the molecular direction mechanism of its pathway are examined. The effects of PSB on the structure and abundance of microbial communities in soil are also described, illustrating the mechanism of how PSB interact with microorganisms in soil and indirectly increase the amount of available phosphorus in soil. And three perspectives are considered in further exploring the PSB mechanism in utilizing a synergistic multi-omics approach, exploring PSB-related regulatory genes in different phosphorus levels and investigating the application of PSB as a microbial fungicide. This paper aims to provide theoretical support for improving the utilization of soil insoluble phosphorus and providing optimal management of elemental phosphorus in the future.