Manipulating geological phosphorus resources for improved production and environmental outcomes during plant establishment.

Phosphorus (P) fertilisers are under scrutiny due to resource constraints and environmental impacts. Simple rock phosphate (RP) modifications with acids and co-applied with microbial inoculum could offer sustainable alternative P fertiliser products. We evaluated the effects of acid-treated rock phosphate (RP) in combination with fungal inoculum on plant establishment, environmental impacts (nutrient leaching) and soil quality in a 5-month pot trial. The treatments were evaluated in a clayey Vertisol and a silty Acrisol using cotton (Gossypium hirsutum) as a model plant. The RP treatments - apart from the unmodified and HCl products - were effective in promoting plant establishment with two of the microbial formulations superior to conventional P fertilisers by an average factor of 2 in both soil types (p < 0.05). All RP products restricted P leaching compared with conventional P fertilisers (p < 0.05), by an average factor of 5 for diammonium phosphate (DAP) in both soil types and 3 for the triple superphosphate TSP (only in Acrisol). Nitrate leaching from all treatments was high although much lower from the RP treatments compared with the conventional fertilisers towards the end of the establishment trial, by an average factor of 1.5 (p < 0.05). Ranking analysis revealed that some RP treatments showed evidence for improved ongoing soil quality, including decreased P leaching and soil acidification risks. Microbial analysis showed complex interactions between treatment and soil type. Nonetheless, inoculum persistence at the end of the plant establishment phase was observed for all pots analysed. Our results demonstrate that relatively simple modifications to RP could pave the way for developing sustainable P fertilisers.

Missing phosphorus legacy of the Anthropocene: Quantifying residual phosphorus in the biosphere.

A defining feature of the Anthropocene is the distortion of the biosphere phosphorus (P) cycle. A relatively sudden acceleration of input fluxes without a concomitant increase in output fluxes has led to net accumulation of P in the terrestrial-aquatic continuum. Over the past century, P has been mined from geological deposits to produce crop fertilizers. When P inputs are not fully removed with harvest of crop biomass, the remaining P accumulates in soils. This residual P is a uniquely anthropogenic pool of P, and its management is critical for agronomic and environmental sustainability. Managing residual P first requires its quantification-but measuring residual P is challenging. In this review, we synthesize approaches to quantifying residual P, with emphasis on advantages, disadvantages, and complementarity. Common approaches to estimate residual P are mass balances, long-term experiments, soil test P trends and chronosequences, with varying suitability or even limitations to distinct spatiotemporal scales. We demonstrate that individual quantification approaches are (i) constrained, (ii) often complementary, and (iii) may be feasible at only certain time-space scales. While some of these challenges are inherent to the quantification approach, in many cases there are surmountable challenges that can be addressed by unifying existing P pool and flux datasets, standardizing and synchronizing data collection on pools and fluxes, and quantifying uncertainty. Though defined as a magnitude, the distribution and speciation of residual P is relatively less understood but shapes its utilization and environmental impacts. The form of residual P will vary by agroecosystem context due to edaphoclimatic-specific transformation of the accumulated P, which has implications for management (e.g., crop usage) and future policies (e.g., lag times in P loading from non-point sources). Quantifying the uncertainty in measuring residual P holds value beyond scientific understanding, as it supports prioritization of monitoring and management resources and inform policy.

The Co-Inoculation Effect on Triticum aestivum Growth with Synthetic Microbial Communities (SynComs) and Their Potential in Agrobiotechnology.

The use of rhizospheric SynComs can be a new and sustainable strategy in the agrobiotechnology sector. The objective of this study was to create the most appropriate SynCom composition; examine the ability to dissolve natural rock phosphate (RP) from Morocco in liquid-modified NBRIP medium; determine organic acids, and phytohormones; and verify plant growth promoting and nutrition uptake effect in the pot experiments of winter wheat (Triticum aestivum). A total of nine different microorganisms were isolated, which belonged to three different genera: Bacillus, Pseudomonas, and Streptomyces. Out of the 21 treatments tested, four SynComs had the best phosphate-dissolving properties: IJAK-27+44+91 (129.17 mg L-1), IIBEI-32+40 (90.95 µg mL-1), IIIDEG-45+41 (122.78 mg L-1), and IIIDEG-45+41+72 (120.78 mg L-1). We demonstrate that these SynComs are capable of producing lactic, acetic, gluconic, malic, oxalic, citric acids, and phytohormones such as indole-3-acetic acid, zeatin, gibberellic acid, and abscisic acid. In pot experiments with winter wheat, we also demonstrated that the designed SynComs were able to effectively colonize the plant root rhizosphere and contributed to more abundant plant growth characteristics and nutrient uptake as uninoculated treatment or uninoculated treatment with superphosphate (NPK 0-19-0). The obtained results show that the SynCom compositions of IJAK-27+44+91, IIBEI-32+40, IIIDEG-45+41, and IIIDEG-45+41+72 can be considered as promising candidates for developing biofertilizers to facilitate P absorption and increase plant nutrition.

Phosphate solubilizing Pseudomonas and Bacillus combined with rock phosphates promoting tomato growth and reducing bacterial canker disease.

Nowadays, sustainable agriculture approaches are based on the use of biofertilizers and biopesticides. Tomato (Solanum lycopersicum L.) rhizosphere could provide rhizobacteria with biofertilizing and biopesticide properties. In this study, bacteria from the rhizosphere of tomato were evaluated in vitro for plant growth promotion (PGP) properties. Five Pseudomonas isolates (PsT-04c, PsT-94s, PsT-116, PsT-124, and PsT-130) and one Bacillus isolate (BaT-68s), with the highest ability to solubilize tricalcium phosphate (TCP) were selected for further molecular identification and characterization. Isolates showed phosphate solubilization up to 195.42 µg mL-1. All isolates showed phosphate solubilization by organic acid production. The six isolates improved seed germination and showed effective root colonization when tomato seeds were coated with isolates at 106 cfu g-1 in axenic soil conditions. Furthermore, the selected isolates were tested for beneficial effects on tomato growth and nutrient status in greenhouse experiments with natural rock phosphate (RP). The results showed that inoculated tomato plants in the presence of RP have a higher shoot and root lengths and weights compared with the control. After 60 days, significant increases in plant Ca, Na, P, protein, and sugar contents were also observed in inoculated seedlings. In addition, inoculated tomato seedlings showed an increase in foliar chlorophyll a and b and total chlorophyll, while no significant changes were observed in chlorophyll fluorescence. In greenhouse, two Pseudomonas isolates, PsT-04c and PsT-130, showed ability to trigger induced systemic resistance in inoculated tomato seedlings when subsequently challenged by Clavibacter michiganensis subsp. michiganensis, the causal agent of tomato bacterial canker. High protection rate (75%) was concomitant to an increase in the resistance indicators: total soluble phenolic compounds, phenylalanine-ammonia lyase, and H2O2. The results strongly demonstrated the effectiveness of phosphate-solubilizing bacteria adapted to rhizosphere as biofertilizers for tomato crops and biopesticides by inducing systemic resistance to the causal agent of tomato bacterial canker disease.

Cultural techniques capture diverse phosphate-solubilizing bacteria in rock phosphate-enriched habitats.

Phosphorus (P) deficiency is a common problem in croplands where phosphate-based fertilizers are regularly used to maintain bioavailable P for plants. However, due to their limited mobility in the soil, there has been an increased interest in microorganisms that can convert insoluble P into a bioavailable form, and their use to develop phosphate-solubilizing bioinoculants as an alternative to the conventional use of P fertilizers. In this study, we proposed two independent experiments and explored two entirely different habitats to trap phosphate-solubilizing bacteria (PSBs). In the first experiment, PSBs were isolated from the rhizoplane of native plant species grown in a rock-phosphate (RP) mining area. A subset of 24 bacterial isolates from 210 rhizoplane morphotypes was selected for the inorganic phosphate solubilizing activities using tricalcium phosphate (TCP) as the sole P source. In the second experiment, we proposed an innovative experimental setup to select mycohyphospheric bacteria associated to arbuscular mycorrhizal fungal hyphae, indigenous of soils where agronomic plant have been grown and trapped in membrane bag filled with RP. A subset of 25 bacterial isolates from 44 mycohyphospheric morphotypes was tested for P solubilizing activities. These two bacterial subsets were then screened for additional plant growth-promoting (PGP) traits, and 16S rDNA sequencing was performed for their identification. Overall, the two isolation experiments resulted in diverse phylogenetic affiliations of the PSB collection, showing only 4 genera (24%) and 5 species (17%) shared between the two communities, thus underlining the value of the two protocols, including the innovative mycohyphospheric isolate selection method, for selecting a greater biodiversity of cultivable PSB. All the rhizoplane and mycohyphospheric PSB were positive for ammonia production. Indol-3-acetic acid (IAA) production was observed for 13 and 20 isolates, respectively among rhizoplane and mycohyphospheric PSB, ranging, respectively, from 32.52 to 330.27 µg mL-1 and from 41.4 to 963.9 µg mL-1. Only five rhizoplane and 12 mycohyphospheric isolates were positively screened for N2 fixation. Four rhizoplane PSB were identified as siderophore producers, while none of the mycohyphospheric isolates were. The phenotype of one PSB rhizoplane isolate, assigned to Pseudomonas, showed four additive PGP activities. Some bacterial strains belonging to the dominant genera Bacillus and Pseudomonas could be considered potential candidates for further formulation of biofertilizer in order to develop bioinoculant consortia that promote plant P nutrition and growth in RP-enriched soils.

Streptomyces rock phosphate ore biomining evaluation in vitro.

The process of extracting metals from rock phosphate ore (RPO) by using microorganisms to convert them into soluble compounds is called biomining. Phosphorus is one of the elements proposed to be extracted from RPO. To understand the role of Streptomyces phospholyticus, 12 isolates of Streptomyces were isolated from RPO, their ability to grow on specific phosphate solubilization medium e.g., National Botanical Research Institute's phosphate growth agar (NBRIP) was studied, and the best strain with a 3 cm clear zone was selected. Its ability to grow at increasing RPO concentrations from 0.01 to 1 kgl-1 was investigated. This strain showed good growth, with extracellular red pigmentation for all concentrations, but no clear zone. In the modified liquid NBRIP, however, the Streptomyces growth patterns of the two concentrations of 0.25 kg and 1 kgl-1 RPO showed growth of single spherical red colonies with rhizoids on the surface, the colonies somehow grew and became embedded in the fine RPO granules. This ability to grow can resist gamma irradiation with a dose of 32 KGy. Within 3 days of growth, acidic and alkaline phosphatase were 76.2 and 67.1 µg p-nitrophenol g-1 ml-1, respectively. The RPO analysis showed that the %P in the ore was 16.5% at the beginning of the experiment, and after Streptomyces biotreatment, this percentage decreased to 8.4%, with a decomposition rate of 50.7%. This study, to our knowledge, is the first to investigate the efficiency of Streptomyces in mining phosphate rock ore in the laboratory, even at high concentrations, and to examine the role of irradiation as a preservative in increasing this efficiency.

Growth stimulation of two legumes (Vicia faba and Pisum sativum) using phosphate-solubilizing bacteria inoculation.

The application of chemical fertilizers for plant growth and protection is one of the reasons for the environment and ecosystem destruction, thus, sustainable agriculture is gaining popularity in research and among farming communities. Although most soils are high in total phosphorus (P), a large portion is unavailable to plants and regarded as a growth-limiting factor. P-solubilizing bacteria (PSB) exploitation is a newly developed bio-solution for enhancing rhizosphere P availability; however, the effect of these bacteria on soil quality and the different phases of plant growth remains unknown. This study aims to evaluate the impact of five strains of PSB, isolated from legume rhizosphere, on the growth of two plants (Vicia faba and Pisum sativum) and certain soil properties. The efficient strains of PSB used are characterized by the P-solubilization, the ACC deaminase activity, the fixation of N, and the IAA, HCN, and siderophores production. The activity of these bacteria is tested in vitro and in vivo under controlled conditions on the growth of the two plants supplemented with the rock P (RP). According to our findings, all PSBs strains outperformed the control in terms of enhancing the growth of the tested legumes with a percentage ranging from 77.78 to 88.88%, respectively. The results showed that all treatments significantly improved plant parameters like nitrogen- (N) and P-content in the plants (67.50, 23.11%), respectively. Also, an increase in the fresh and dry weights of above- (41.17, 38.57%) and below-ground biomasses (56.6, 42.28%), respectively. Compared to the control, this leads to an increase of 72% in root length, 40.91% in plant dry weight, and 40.07% in fresh weight. Rhizospheric soil in PSBs treatments displayed high levels of N, P, and organic matter. All treatments were found to have significantly higher levels of alkaline phosphatase, basal soil respiration, and ß-glucosidase activity than the control. It is concluded that multi-traits PSB can be an alternative for utilizing chemical fertilizers to enhance soil quality and plant growth. Despite the potency of PSBs, its use as a source for the development of sustainable agriculture implies focusing on crop species and adaptation, stress tolerance and climate resilience.

Phosphate-Solubilizing Bacteria with Low-Solubility Fertilizer Improve Soil P Availability and Yield of Kikuyu Grass.

Inoculation with phosphate-solubilizing bacteria (PSB) and the application of phosphorus (P) sources can improve soil P availability, enhancing the sustainability and efficiency of agricultural systems. The implementation of this technology in perennial grasses, such as Kikuyu grass, for cattle feed in soils with high P retention, such as Andisols, has been little explored. The objective of this study was to evaluate the productive response of Kikuyu grass and soil P dynamics to BSF inoculation with different P sources. The experiment was conducted on a Kikuyu pasture, which was evaluated for 18 months (September 2020 to March 2022). Three P fertilizers with different solubility levels were applied: diammonium phosphate (DAP) (high-solubility), rock phosphate (RP), and compost (OM) (low-solubility). Moreover, the inoculation of a PSB consortium (Azospirillum brasilense D7, Rhizobium leguminosarum T88 and Herbaspirillum sp. AP21) was tested. Inoculation with PSB and fertilization with rock phosphate (RP) increased soil labile P and acid phosphomonoesterase activity. Increased grass yield and quality were related with higher soil inorganic P (Pi) availability. This study validated, under field conditions, the benefits of PSB inoculation for soil P availability and Kikuyu grass productivity.

Role of Rahnella aquatilis AZO16M2 in Phosphate Solubilization and Ex Vitro Acclimatization of Musa acuminata var. Valery.

Rahnella aquatilis AZO16M2, was characterized for its phosphate solubilization capacity to improve the establishment and survival of Musa acuminata var. Valery seedlings under ex-acclimation. Three phosphorus sources (Rock Phosphate (RF), Ca3(PO4)2 and K2HPO4) and two types of substrate (sand:vermiculite (1:1) and Premix N°8) were selected. The factorial analysis of variance (p < 0.05) showed that R. aquatilis AZO16M2 (OQ256130) solubilizes Ca3(PO4)2 in solid medium, with a Solubilization Index (SI) of 3.77 at 28 °C (pH 6.8). In liquid medium, it was observed that R. aquatilis produced 29.6 mg/L soluble P (pH 4.4), and synthesized organic acids (oxalic, D-gluconic, 2-ketogluconic and malic), Indole Acetic Acid (IAA) (33.90 ppm) and siderophores (+). Additionally, acid and alkaline phosphatases (2.59 and 2.56 µg pNP/mL/min) were detected. The presence of the pyrroloquinoline-quinone (PQQ) cofactor gene was confirmed. After inoculating AZO16M2 to M. acuminata in sand:vermiculite with RF, the chlorophyll content was 42.38 SPAD (Soil Plant Analysis Development). Aerial fresh weight (AFW), aerial dry weight (ADW) and root dry weight (RDW) were superior to the control by 64.15%, 60.53% and 43.48%, respectively. In Premix N°8 with RF and R. aquatilis, 8.91% longer roots were obtained, with 35.58% and 18.76% more AFW and RFW compared with the control as well as 94.45 SPAD. With Ca3(PO4)2, values exceeded the control by 14.15% RFW, with 45.45 SPAD. Rahnella aquatilis AZO16M2 favored the ex-climatization of M. acuminata through improving seedling establishment and survival.

Improving the efficiency of phosphate rocks combined with phosphate solubilizing Actinomycetota to increase wheat growth under alkaline and acidic soils.

Low availability of phosphorus (P) in both acidic and alkaline soils is a major problem for sustainable improvement in wheat crops yield. Optimization of crops productivity can be achieved by increasing the bioavailability of P by phosphate solubilizing Actinomycetota (PSA). However, their effectiveness may vary with changing agro-climatic conditions. In this regard, a greenhouse experiment was conducted to assess the interaction inoculation of five potential PSA (P16-P18-BC3-BC10 and BC11) and RPs (RP1- RP2-RP3 and RP4) on the growth and yield of wheat crop in unsterilized P- deficient alkaline and acidic soils. Their performance was compared with single super phosphate (TSP) and reactive RP (BG4). The in-vitro tests showed that all PSA colonize wheat root and form a strong biofilm except Streptomyces anulatus strain P16. Our findings revealed that all PSA significantly improve the shoot/root dry weights, spike biomass, chlorophyll contents as well as nutrients uptake in plants fertilized with RP3 and RP4. However, the combined application of Nocardiopsis alba BC11 along with RP4 in alkaline soil, was effective in optimizing wheat yield attributes and improve the yield biomass up to 19.7% as compared to the triple superphosphate (TSP). This study supports the view that the inoculation with Nocardiopsis alba BC11 has a broad RP solubilization and could alleviate the agricultural losses due to P limitation in acidic and alkaline soils.

Isolation of Phosphate-Solubilizing Microorganisms and the Formulation of Biofertilizer for Sustainable Processing of Phosphate Rock.

As phosphorus (P) bioavailability is limited in arable lands, chemical fertilizers are being used by farmers to increase crop production. Phosphate-solubilizing microorganisms (PSMs) increase the bioavailability of sparingly soluble inorganic and organic soil phosphorus. Therefore, the current study was an effort to evaluate the phosphate-solubilizing efficiency of PSMs using tricalcium phosphate (TCP) and Eppawala rock phosphate (ERP). The efficiency of phosphate solubilization by a series of identified isolates was compared using TCP (5 g L-1) and ERP (5 g L-1) as a P source in Pikovskava's broth. Twelve microbial isolates that showed a higher efficiency in phosphate solubilization were selected for the production of the biofertilizer. The isolate F10 in ERP broth was characterized by the highest significant level of available phosphorus (896.98 ± 10.41) mg L-1, followed by F5 (Aspergillus sp.) in TCP broth 991.43 ± 1.37 mg L-1. A pot trial was carried out by using Capsicum annuum L. as the test plant in two soil conditions: sterilized soil and non-sterilized soil with six treatments and four replicates. The significantly highest plant height, leaf length, and width were shown by chili plants treated with the formulated biofertilizer. Therefore, the application of native PSMs appeared to be an efficient method of solubilizing sparingly soluble P compounds into plant-available forms.

Screening of potential phosphate solubilizing bacteria inoculants should consider the contrast in phosphorus bio-solubilization rate along with plant growth promotion and phosphorus use efficiency.

AIMS: Although phosphate solubilizing bacteria (PSB) have been globally reported to improve soil phosphorus (P) availability and plant growth, technical gaps such as the lack of an ideal screening approach, is yet to be addressed. The potential of non-halo-forming PSB remains underestimated because of the currently adopted screening protocols that exclusively consider halo-forming and PSB with high phosphorus solubilization (PS) capacities. Yet, caution should be taken to properly assess PSB with contrasting PS rates regardless of the presence or absence of the solubilization halo. METHODS AND RESULTS: This study sought to examine the PS rate and plant growth promotion ability of 12 PSB categorized as high PSB (H-PSB), medium PSB (M-PSB), and low PSB (L-PSB) based on their PS rates of rock phosphate (RP). The non-halo-forming PSB Arthrobacter pascens was categorized as H-PSB, which might have been eliminated during the classical screening process. In addition, induction of organic acids and phosphatase activity in rhizosphere soils by H-, M-, and L-PSB was proportional to increased wheat P content by 143.22, 154.21, and 77.76 mg P g-1 compared to uninoculated plants (18.1 mg P g-1). CONCLUSIONS: Isolates considered as M- and L-PSB could positively influence wheat above-ground physiology and root traits as high as H-PSB. In addition, non-halo-forming PSB revealed significant PS rates along with positive effects on plant growth as high as halo-forming PSB.

Glomerales Dominate Arbuscular Mycorrhizal Fungal Communities Associated with Spontaneous Plants in Phosphate-Rich Soils of Former Rock Phosphate Mining Sites.

Arbuscular mycorrhizal fungi (AMF) are key drivers of soil functioning. They interact with multiple soil parameters, notably, phosphorus (P). In this work, AMF communities of native plants grown spontaneously on former mining sites either enriched (P sites) or not enriched with P (nP sites) by mining cuttings of rock phosphate (RP) were studied. No significant differences were observed in the root mycorrhizal rates of the plants when comparing P and nP sites. The assessment of AMF diversity and community structure using Illumina MiSeq metabarcoding and targeting 18S rDNA in roots and rhizospheric soils showed a total of 318 Amplicon Sequence Variants (ASVs) of Glomeromycota phylum. No significant difference in the diversity was found between P and nP sites. Glomeraceae species were largely dominant, formed a fungal core of 26 ASVs, and were persistent and abundant in all sites. In the P soils, eight ASVs were identified by indicator species analysis. A trend towards an increase in Diversisporaceae and Claroideoglomeraceae and a reduction in Paraglomeraceae and Glomeraceae were noticed. These results provide new insights into AMF ecology in former RP mining sites; they document that P concentration is a driver of AMF community structures in soils enriched in RP long term but also suggest an influence of land disturbance, ecosystem self-restoration, and AMF life history strategies as drivers of AMF community profiles.

Promoting growth and production of sunchoke (Helianthus tuberosus) by co-inoculation with phosphate solubilizing bacteria and arbuscular mycorrhizal fungi under drought.

Due to different functions of phosphate solubilizing bacteria (PSB) and arbuscular mycorrhizal fungi (AMF), their potential synergistic effects on enhancing plant growth and yield are worth investigating, especially under adverse conditions. This work focused on the isolation of PSB and characterization for their plant growth promoting properties under drought. The most efficient P solubilizing bacterium was isolated and identified as Burkholderia vietnamiensis strain KKUT8-1. Then, a factorial experiment on the performance of sunchoke (Helianthus tuberosus) was set up with four factors, viz., PSB (presence or absence of KKUT8-1), AMF (presence or absence of Rhizophagus aggregatus), rock phosphate (RP; added or not) and moisture (well-watered (WW) or drought (DS) conditions). Sunchoke performance was enhanced by the presence of AMF, whereas addition of PSB had a positive effect on SPAD values and inulin concentration. Drought reduced plant performance, while addition of RP reduced photosynthetic rate. There was little evidence for synergistic effects between PSB and AMF, except for SPAD values and inulin concentration. Plants that were co-inoculated with AMF and PSB had highest SPAD value, shoot diameter, leaf area, leaf number, chlorophyll concentration, plant biomass, tuber production, root growth and total soluble sugar concentration. Co-inoculated plants also had increased plant water status, reduced electrolyte leakage, and reduced malondialdehyde and proline concentration. Strain KKUT8-1 is the first strain of B. vietnamiensis capable of promoting growth and yield of sunchoke. Enhanced production of sunchoke by a combination of AMF and PSB was much better than the application of RP. Our finding offers an opportunity to develop combinations of biological inoculants for increasing the growth and production of sunchoke under drought in the future.

Isolation and characterization of phosphate solubilizing bacteria naturally colonizing legumes rhizosphere in Morocco.

Low-cost and environmentally friendly agricultural practices have received increasing attention in recent years. Developing microbial inoculants containing phosphate (P) solubilizing bacteria (PSB) represents an emerging biological solution to improve rhizosphere P availability. The present study aims to explore PSB strains isolated from soils located at different bioclimatic stages in Morocco and present in various legumes rhizosphere to improve agronomic microbial fertilizer's effectiveness. It was also aimed to test the isolated strains for their ability to solubilize P in NBRIP medium with Tricalcium P (Ca3 (PO4)2) (TCP), rock phosphate (RP), and their combination as a source of phosphorus, by (22) experiment design. Bacterial strains with a high P solubility index (PSI) were selected, characterized, and compared to commercial control. The vanadate-molybdate method was used to estimate P solubilization activity. Stress tolerance to salinity, acidity, drought, and temperature was tested. From all isolated strains (64), 12 were screened as promising biotechnological interest because of their P solubilization and their good resistance to different drastic conditions. Besides, the strain WJEF15 showed the most P solubility efficiency in NBRIP solid medium with a PSI of 4.1; while the WJEF61 strain was located as the most efficient strain in NBRIP-TCP liquid medium by releasing 147.62 mg.l-1 of soluble P. In contrast, in the NBRIP-RP medium, the strain WJEF15 presented maximum solubilization with 25.16 mg.l-1. The experiment design showed that a combination of RP and TCP with max level progressively increases P solubilization by 20.58%, while the WJEF63 strain has the most efficient concentration of 102.69 mg.l-1. Indeed, among the selected strains, four strains were able to limit tested fungi growth. Thus, results reveal a potential effect of selecting PSBs to support cropping cultures as plant growth-promoting rhizobacteria (PGPR).

Impact of aeration rate on phosphorus conversion and bacterial community dynamics in phosphorus-enriched composting.

This study was to investigate the effects of different aeration rates on phosphorus (P) conversion and bacterial community dynamics in P-enriched composting by 16S rRNA gene sequencing, sequential P fractionation, network analysis and structural equation model (SEM). Results indicated that Olsen P content increased by 138 %, 150 %, 121 % after composting with aeration rate (L kg-1 DM min-1) at 0.2 (AR0.2), 0.4 (AR0.4) and 0.6 (AR0.6). AR0.4 was more conducive to enhance P solubilization efficacy and available P accumulation. Redundancy analysis indicated Lactobacillus, Spartobacteria and Pseudomonas were key bacteria associated with HCl-Pi especially in AR0.2 and AR0.4. Network analysis showed that increased aeration rate enhanced the connection and function homoplasy among modules and AR0.4 had more orderly community organization for key bacteria to solubilize P in directly and indirectly biotic way. SEM suggested indirectly biotic P-solubilization had more contribution than directly biotic way mainly by phosphate-solubilizing bacteria.

Influence of carbon-to-phosphorus ratios on phosphorus fractions transformation and bacterial community succession in phosphorus-enriched composting.

This study aims to assess the effect of different carbon-to-phosphorus (C:P) ratios on phosphorus (P) fractions transformation, bacterial community succession and microbial P-solubilizing function in kitchen waste composting with rock phosphate (RP) amendment and phosphate-solubilizing bacteria (PSB) inoculation. Results indicated that initial C:P ratio at 50 enhanced organic carbon degradation, available P (AP) accumulation, the amount of PSB and pqqC gene abundance in composting but higher C:P ratio increased microbial biomass phosphorus (MBP) content. Redundancy analysis showed C:P ratios, PSB amount and pqqC gene abundance greatly affected bacterial community diversity and composition. Network analysis indicated that lower C:P ratio enhanced the interaction frequency in core bacterial network for AP transformation. Variance partitioning analysis abiotic factors contributed more to MBP and AP conversion. The study revealed that C:P ratio could directly drive PSB to regulate P fractions and the accumulation of MBP or AP in P-enriched composting.

In-situ stabilization of potentially toxic elements in two industrial polluted soils ameliorated with rock phosphate-modified biochars.

The present study was aimed at determining the efficacy of rock phosphate (RP) 3% loaded in a green coconut shell, chicken manure, and vegetable waste to make green coconut-modified biochar (GMB), chicken manure modified-biochar (CMB), and vegetable waste-modified biochar (VMB) in the fixation of Cr, Pb, Cu, Zn, Ni, and Cd in Sharafi goth and Malir polluted soils. The impact of RP impregnated with organic waste material to produce modified biochars (MBs) on stabilizing PTEs from polluted soils and reducing their uptake by mustard plant has not yet been thoroughly investigated. All modified BCs in 0.5, 1, and 2% doses were used to stabilize Cr, Pb, Cu, Zn, Ni, and Cd in two polluted soils and to reduce their uptake by the mustard plant. The obtained results revealed that the maximum mustard fresh biomass was 17.8% higher with GMB 1% in Sharafi goth polluted soil and 25% higher with VMB 0.5% in Malir polluted soil than in the control treatment. After applying modified BCs, immobilization of Cr, Pb, Cu, Ni, and Cd was observed in both soils and it reduced the uptake of these elements by mustard plants. On the other hand, although Zn mobilization increased by 0.38% for CMB 0.5% and by 5.9% for VMB 0.5% in Sharafi goth polluted soil, as well as by 3.15% for GMB 1%, 6.34% for GMB 2%, and 4.78% for VMB 0.5% in Malir polluted soil, this was due to changes in soil pH and OM. It was found that GMB 1%, CMB 0.5%, and VMB 0.5% have the potential to increase Zn uptake by mustard, while VMB 2% can reduce the element uptake by the plant. Redundancy analysis showed that soil chemical parameters were negatively correlated with PTEs in both soils and reduced their uptake by mustard. The present study revealed that MBs can stabilize PTEs in industrial and wastewater soils polluted with multiple metals and reduce their uptake by plants.

Effect of Arbuscular Mycorrhizal Fungi Isolated From Rock Phosphate Mine and Agricultural Soil on the Improvement of Wheat Plant Growth.

The improvement of plant growth and yield becomes crucial to feed the rising world population, especially in harsh conditions, drought, salt stress, lack of nutrition, and many other challenges. To cope with these stresses, plants developed an adaptation strategy (mycorrhiza), which is an efficient way to reinforce their growth and resistance. For this purpose, we studied the influence of mycorrhizal fungi isolated from a natural rock phosphate mine in the vicinity of some native plants and agricultural soil to assess their capacity in increasing the growth, nutritional profile improvement, and biochemical parameters in the inoculated wheat plants. Results showed a high diversity of isolated arbuscular mycorrhizal fungi (AMF) spores in the agricultural soil, and less diversity in the natural phosphate samples, where three main genera were identified: glomus, gigaspora, and acaulospora. The chlorophyll content increased by 116% in the native inoculum (NM) flowed by Glomus sp2 from agricultural soil (98%) compared to non-mycorrhized plants, which significantly impact the growth and plant biomass (an increase of 90 and 73%, respectively). The same rate of change was shown on total phenolic compounds with an increase of 64% in the plants inoculated with Glomus sp2 in the presence of TSP, compared to the non-mycorrhized plants. In conclusion, the inoculation of wheat plants with AMF spores improved plants' growth via the increase in the density of the root system, which implies better assimilation of nutrients, especially in mycorrhizal plants with phosphorus fertilization regime, triple superphosphate (TSP) or natural rock phosphate (RP). This improvement of the physiological and biochemical parameters (chlorophyll contents and phenolic compound) of the treated plants reflected the positive impact of AMF, especially those originating from RP. AMF in phosphate mine could be an important source of inoculum to improve plant nutrient efficiency with the direct use of RP as fertilizer.

Streptomycetaceae and Promicromonosporaceae: Two Actinomycetes Families from Moroccan Oat Soils Enhancing Solubilization of Natural Phosphate.

Soil actinomycetes explorations appear to be an efficient alternative as biofertilizers to optimize the use of phosphorus (P) resources and enhance plant growth. This research aimed to explore the distribution of actinomycetes isolated from four different rhizospheric Moroccan oat soils and to investigate their potential for P solubilization. The distribution of actinomycetes was significantly more abundant in Settat (9.68%), Tangier (7.38%), and Beni Mellal (6.87%) than in the Merchouch-Rabat (4.90%) region. A total of 235 actinomycete strains were isolated from all sites and tested for their ability to grow on a synthetic minimum medium (SMM) containing insoluble natural rock phosphate (RP) or synthetic tricalcium phosphate (TCP) as the unique P source. One hundred forty-three isolates (60.8%) had the ability to grow in the SMM with RP whereas only twenty-five isolates (17%) had the most active growth using the SMM with TCP. Eight isolates with the most active growth in solid SMM were selected for their P solubilization abilities in liquid SMM cultures. The highest amount of P solubilized was 163.8 µg/mL for RP and 110.27 µg/mL for TCP after 5 days of culture. The biosolubilization process of AM2, the most efficient RP and TCP solubilizing strain, probably implied the highest excretion of siderophore substances. Eight of these strains were shown to belong to the Streptomyces genus and one to the Promicromonospora genus. These findings bolster the phosphate biosolubilization abilities of actinomycetes and may participate in increasing agricultural yields in an eco-efficient and environmentally friendly manner.