Phosphate Solubilizing Bacteria Inoculation Research Articles

Effects and mechanisms of phosphate solubilizing bacteria on enhancing phytoextraction of lead from contaminated soil by Celosia cristata L.

Phosphate solubilizing bacteria (PSB)-assisted phytoextraction can enhance the removal of toxic metals by plants from contaminated soil. Here, we investigated the promotion effects of a Pb-tolerant PSB strain, Leclercia adecarboxylata L1-5, on assisting Pb phytoextraction by Celosia cristata L.. The results showed that PSB inoculation could increase the plant shoot and root biomass by 34.90% and 55.56% when the Pb concentration was 800 mg kg−1. Pb contents in the root and shoot were enhanced 3.06 and 0.72-fold by PSB inoculation, resulting in a bioaccumulation factor (BCFaboveground) of 0.2, a translocation factor (TF) of 1.92, and a maximum total Pb extraction amount of 222.94 μg kg−1. The positive effects of PSB on Pb bioaccumulation by C. cristata L. could be attributed to its abilities of increasing soil available phosphorus. PSB inoculation benefited osmotic potential balance and membrane stability in the plant leaves, as evidenced by 2.39-fold increase of the soluble protein, 71.39% decrease of malondialdehyde and 74.31% decrease of hydrogen peroxide. The main mechanism of the enhancement of Pb phytoextraction efficiency induced by PSB inoculation could be summarized as helping Pb absorption by root elongation, and increasing endurable Pb concentration by osmotic regulation and detoxification ability optimization. This work demonstrated that PSB combined with C. cristata L. was an excellent candidate for lead extraction and could be considered as an effective way for soil lead remediation in the future.

Phosphate Solubilizing Bacteria (PSB) Improve Phosphorus Availability from Various Sources in Alkaline Soils

Phosphorus (P) is one of the major essential macronutrients for plants, applied to soil in the form of phosphatic fertilizers and organic manures. The application of PSB to soils can replace or partially reduce use of inorganic P fertilizers and could be one of the cost effective, highly efficient, and sustainable approaches to conserve P resources. The aim of the study was to evaluate the role of PSB in phosphorus (P) availability from organic, mineral and natural sources. For this purpose, a laboratory incubation experiment was conducted at the University of Agriculture Peshawar. The experiment was consisting of four sources of P [poultry manure (PM), farm yard manure (FYM), rock phosphate (RP) and single supper phosphate (SSP)] for obtaining 45 mg P2O5 kg-1 and two types of inoculation (control and PSB) arranged in two factorial complete randomized design with three replications. Resultantly, PSB inoculation significantly improved. P availability at all incubation interval except day zero. A 3.4%, 5.4%, 12% and 16 % increased were observed in P as compared to control, at day 7, 14, 28 and 56 respectively. Similarly, significant differences were observed in P release for P sources at all incubation intervals. Initially higher P release was observed for SSP but at day 14 onward PM and FYM proved to be the best P releasable sources as compared to mineral P sources. RP released the lowest P at all incubation intervals however it performed statistically at par to SSP at 56 days. The significant interactive effect of P sources and PSB at day 28 and 56 demonstrated that soil receiving P from organic sources inoculated with PSB released higher P than other treatments combination. Thus, it is suggested that P must be applied from organic P sources (PM and FYM) along with PSB inoculation for better P nutrition and crop yield.

Relationships among phosphatase activities, functional genes and soil properties following amendment with the bacterium Burkholderia sp. ZP‐4

AbstractPhosphorus (P) limitation is common in subtropical and tropical regions. Although phosphate‐solubilizing bacteria (PSB) can transform soil P fractions and enhance soil P availability, the mechanism regarding the linkage between PSB abundance and soil P fractions transformation were still unknown. In this study, Burkholderia sp. ZP‐4, a PSB strain, was inoculated into subtropical bamboo forest soil at the inoculation rates of 0% (bacterial suspension: soil weight = v: w, the control), 2% (2%IR), 6% (6%IR) and 10% (10%IR). The changes in soil P fractions, bacterial community, phosphatase activities, P transforming functional genes and soil properties were also determined after the PSB inoculation. Compared with the control, soil inorganic P extracted by deionized water (H2O‐Pi) and extracted by sodium bicarbonate (NaHCO3‐Pi) in the 6%IR treatments were increased 45.35% and 16.05%, respectively. The lowest content of residual P (residual‐P) was in the 6%IR treatment among the four treatments. The 6%IR treatment contributed to stimulating and inducing soil acid phosphatase activity and P cycling genes (phoD and phoC) abundances, relative to the control. The PSB inoculation significantly decreased soil pH but increased soil available nitrogen P supplies among all treatments. Simultaneously, the PSB inoculation also significantly changed soil bacterial community. The transformation of P fractions in the 6%IR was more efficient than the other treatments, implying that 6% is the proper inoculation rate of functional Burkholderia for accelerating P cycling at subtropical bamboo forest soil. Our findings will provide a scientific guidance for the application of biofertilizer.

Additive Response of Biofertilizers on Seed Yield and Quality in Cowpea

Background: Cowpea is a precious crop for farmers with limited resources. The crop’s yield potential was constrained coupled with poor seed management methods, a lack of high yielding varieties and improper input use. Seed inoculation with biofertilizer is critical for increasing nutrient utilization efficiency and crop yield via nitrogen fixation and nodulations. With this in mind, a study was performed to appraise the influence of pre-sowing seed inoculation on initial seed quality, crop growth, seed yield, seed biochemical content and seed quality in cowpea, both in the laboratory and field. Methods: Cowpea seeds were imposed with different bio-inoculants viz., Rhizobium @ 600 g/ha, PSB @ 600 g/ha, VAM @ 600 g/ha and Pseudomonas @ 10 g/kg as single treatment and in combined inoculations. The above treated seeds along with control were evaluated for seed quality under laboratory condition and crop growth and yield potential under field condition. Result: Rhizobium inoculation (600 g/ha) and phosphate solubilizing bacteria inoculation (600 g/ha) were added to the seeds before they were sown. This led to better growth, yield and seed quality.

Comparative efficacy of phosphorous supplements with phosphate solubilizing bacteria for optimizing wheat yield in calcareous soils

Phosphorus (P) deficiency is the main hurdle in achieving sustainable crop production ps especially in calcareous soils. Using bio-fertilizers like phosphate solubilizing bacteria (PSB) could be a useful approach for sustainable P management as they improve P availability in soil via dissolution, desorption and mineralization reactions. In addition, application of organic amendments with PSB could further ameliorate soil conditions for sustainable management of immobilized nutrients in calcarious soils. Therefore, we performed pot experiment to study the role of PSB in nullifying antagonistic effects of liming (4.78, 10, 15 and 20%) on P availability from poultry manure (PM), farm yard manure (FYM), single super phosphate (SSP) and rock phosphate (RP) in alkaline soils. PSB inoculation improved wheat growth, P availability and stimulated soil acidification over control regardless of P sources and lime levels. Soil calcification adversely affected plant growth, P nutrition, induced soil salinity and alkalinity, however, PSB and manures application potentially nullified such harmful effects over mentioned traits. Individually, organic sources were superior than mineral sources however, the performance of mineral fertilizers with PSB was at par to sole application of manures. Furthermore, application of RP with PSB proved as effective as sole SSP. Therefore, using PSB as bio-fertilizer has huge potential for improving P availability in calcareous soils.

APLIKASI PUPUK ORGANIK DAN BAKTERI PELARUT FOSFAT UNTUK MENINGKATKAN PERTUMBUHAN DAN HASIL TANAMAN JAGUNG MANIS MANIS (Zea mays saccaharta sturt L.)

The use of organic matters on sweet corn cultivation is focused to decrease the utilization of chemical substances for minimizing environmental degradation. An experiment was conducted at Ujung Berung Indah Residence, Ujung Berung Districts, Bandung City (± 780 m asl.) from April to July 2020. The Aims of this research were to determine the suitable and effective inoculant to increase the growth of sweet corn plants. The sweet corn variety used was Bonanza F1 and the PSB inoculant that used was Bacillus Laterosporus. The organic fertilizers were compost, chicken and cow dung, and phosphate solubilizing bacteria (PSB), as a biofertilizer. A randomized block design with three replications was utilized in this experiment. The treatments consisted of without organic fertilizers or PSB (control) (K), inoculation of PSB (P1), application of compost (P2), (4) application of chicken and cow dung (P3), and application of the chemical fertilizer (NPK) (P4). The results showed that the application of organic fertilizers and PSB increased the growth of sweet corn plants after harvesting. The inoculation of PSB resulted in highest plant height compared to control and the highest sweet corn yield compared to the control treatment, and even it was higher than the yield caused by the application of the chemical fertilizer.

Phosphate solubilizing bacteria inoculated low-grade rock phosphate can supplement P fertilizer to grow wheat in sub-tropical inceptisol

Soil phosphorus (P) despite being an important element for plant growth, its high reactivity and low solubility has challenged the farming community for its efficient utilization. P fertilizers are produced from high grade rock phosphates. Reserve of this non-renewable resource is getting exhausted very rapidly. That establishes the need of using non-conventional P sources to grow crops. In this study, low grade rock phosphates (LGRP) were used as alternate P source to grow wheat in Inceptisol. Different quantities of phosphate solubilizing bacteria (PSB) inoculated LGRP were applied in incubation and pot experiments and were compared with a commercial P fertilizer. It was hypothesized that PSB inoculation would increase P solubility from LGRP and reduce P fixation in soil, thus improve supply parameter and increase P availability to the crop. Short term P dynamics at three different growth stages of wheat, enzyme activities, P-fixation and adsorption chemistry were studied. Incubation experiment established that PSB inoculated LGRP can supply significantly higher amount of P as compared to untreated LGRP. It also proved the potentiality of PSB inoculated LGRP treatment to maintain better supply of P in soil for long term. Pot experiment revealed that combined application of PSB inoculated LGRP + di-ammonium phosphate (DAP) can supplement 50% P fertilizer and maintain similar yield and P uptake as compared to DAP treatment. Applied PSB solubilized P from LGRP and soil, also prevented P fixation in soil by producing organic acids, siderophores, phosphatase enzymes. Thereby, application of PSB inoculated LGRP provided steady supply of available and saloid P for wheat throughout the growth stages and synchronised P supply with its demand. Application of PSB inoculated LGRP reduced the value of P adsorption maxima by ∼18% and bonding energy related constant of P-fixation by ∼11%; while value of P supply parameter enhanced by ∼14% over no PSB application. The PSB inoculated LGRP application enhanced inherent microbial activities by 10–24%, slashed P-fixation capacity by altering P adsorption chemistry and optimised P supply parameter. Thus, application of PSB inoculated LGRP could be recommended to crops to save ∼50% of the commercial P-fertilizer without affecting crop yields.

Combined inoculation of phosphate solubilizing bacteria with mycorrhizae to alleviate the phosphate deficiency in Banana

Combined inoculation of phosphate solubilizing bacteria with mycorrhizae to alleviate the phosphate deficiency in Banana

Low-temperature straw biochar: Sustainable approach for sustaining higher survival of B. megaterium and managing phosphorus deficiency in the soil

Inoculation of phosphate-solubilizing bacteria (PSB) is a sustainable approach to increase the available P content in soils for crop production. This application, however, is constrained by the low survival rate of PSB in the field. Biochar, a carbon-rich biomaterial with a well-developed porous structure, has recently emerged as an appealing option to maintain the population size of inoculants in the soil. The efficacy of biochar as a PSB carrier is primarily determined by its physicochemical properties, which are dominated by the feedstocks and the pyrolysis temperatures. This study demonstrated a comprehensive assessment of the efficacy of straw-derived biochars prepared from different feedstocks (i.e., crop straws from cotton, peanut, maize, soybean, and wheat) and pyrolysis temperatures (i.e., 300 and 600 °C). We employed B. megaterium carrying green fluorescence protein and evaluated its survival rate and phosphate-solubilizing performance in various inoculated biochars that have distinct physicochemical properties. Our results showed that the pyrolysis temperature is more determinant of the beneficial effect of straw biochar than the feedstock species. Cotton straw biochar pyrolyzed at low temperature (i.e., 300 °C) sustained a survival rate of 6.17% for the B. megaterium and thereby entailed a significant increase in available P in soil by 30.05 mg kg−1 soil, which were nearly 18-fold and 8-fold higher than that of the no carrier treatment respectively. The performance of biochar-assisted PSB was dominant-negatively affected by the increasing pH, ash content, surface area, and total pore volume of biochar, while larger H/C ratio, water holding capacity, pore size, and surface hydrophobicity were predominantly conducive to the colonization and survival of PSB. The results of this study were expected to provide valuable guidance for biochar preparation in practice to enhance the survival and activity of PSB and maximize the utility of PSB as sustainable phosphorus fertilizer with economic applicability.

Coupling phosphate-solubilizing bacteria (PSB) with inorganic phosphorus fertilizer improves mungbean (Vigna radiata) phosphorus acquisition, nitrogen fixation, and yield in alkaline-calcareous soil

To overcome the problems associated with soil phosphorus (P) insolubility, soil inoculation with phosphate-solubilizing bacteria (PSB) can be used. In a field experiment, we evaluated the efficacy of PSB in enhancing mungbean P acquisition, nitrogen (N) fixation, and morphological and yield traits in alkaline-calcareous soil when added together with P as single superphosphate (SSP) or rock phosphate (RP) at 45 or 90 kg P2O5 ha−1. Coupling PSB with mineral P fertilizers (SSP & RP) improved P use efficiency, mungbean P acquisition, N2 fixation, nodulation, NP uptake, and the morphological and yield-related traits of mungbeans compared with non-fertilized controls and plots received P from mineral sources alone. Soil PSB inoculation with mineral P also improved post-harvest soil fertility relative to pre-harvest by improving soil organic matter from 0.61% to 0.70%, lowering pH from 7.74 to 7.68, and improving soil total N from 0.04 to 0.09%, ABDTPA-extractable P from 2.07 to 3.44 mg kg−1, and potassium (K) concentrations from 100.27 to 129.45 mg kg−1. When combined with PSB, RP generally performed better than SSP. Moreover, there was a significant correlation between soil N and plant N, while the correlation between soil P and plant P was non-significant. The correlation between soil organic matter content and NP uptake by mungbeans was also non-significant. Therefore, adding P as RP at 45–90 kg ha−1, together with PSB inoculation, can be recommended for improving mungbean P acquisition, use efficiency, optimum N2 fixation, and yield in alkaline-calcareous soils.

A Review on Vermicompost Enrichment: In Prospect of Village Level

Cow dung is very useful as fertilizer, with help of earthworms a unique product vermicompost is formed. Importance of vermicompost over chemical fertilizer is accepted by all. There is plenty of cow dung but vermi tank are limited, here we have discussed some innovations to fasten the process of maturation by using decomposer, bacteria and fungi species, here we have reviewed different methods. It found significantly higher phosphorus percent in slurry method, slight more K percent compare to conventional method, not much difference in N content are reported, almost two folds increase in useful bacteria fungi and azotobacter population are recorded as compare to conventional. There are reported increase in N and P contents of manure after inoculation of phosphate solubilizing bacteria (PSB) and N-fixing bacteria. Waste decomposer which contains fungi Trichoderma viridae and strains of bacteria Pseudomonus fluorescence and Azotobactor chroococcum also impart positive effects on nutrients composition in manure and also a symbiosis effect on earthworm population. The method of Pile composting enriched with decomposer will be prove as very useful for huge quantity waste with less resources and time.

Perspectives for Biochar as a vehicle for inoculation of phosphate solubilizing bacteria: a review

Phosphorus (P) plays a vital role in many aspects of plant growth and development. The low amount of available P in agricultural soils reduces crop productivity and phosphate fertilizers are often applied. However, due to the high affinity of P for the soil constituents, the availability of this element becomes limited to plants. Thus, alternative, ecological, and low-cost techniques have been studied to improve P acquisition by crops. Microorganisms able to solubilize P, mainly phosphate-solubilizing bacteria (PSB) have stood out, since they offer an approach to overcome P scarcity by their introduction in agricultural systems via inoculants. In this paper, we showed the potential of P-solubilizing microorganisms and their mechanisms of action, the potential of different inoculation vehicles, also highlighting the biochar as a viable biological product for production of inoculants. The combined effects of these factors (PSB and biochar) add several benefits to the soil-plant system. Results from this review demonstrate that biochar amendments have great potential as a vehicle for inoculation of PSB. However, studies of biochar combined with PSB is still incipient. Future research should focus efforts on exploring highly efficient strains, optimizing conditions, and assessing several sources of waste for production of biochar and their efficiency in field experiments.

Interaction Between Halotolerant Phosphate-Solubilizing Bacteria (Providencia rettgeri Strain TPM23) and Rock Phosphate Improves Soil Biochemical Properties and Peanut Growth in Saline Soil.

Soil salinity has adverse effects on soil microbial activity and nutrient cycles and therefore limits crop growth and yield. Amendments with halotolerant phosphate-solubilizing bacteria (PSB) and rock phosphate (RP) may improve properties of saline soil. In this study, we investigated the effects of RP either alone or in combination with PSB (Providencia rettgeri strain TPM23) on peanut growth and soil quality in a saline soil. With the combined application of RP and PSB, plant length and biomass (roots and shoots) and uptake of phosphorus (P), nitrogen (N), and potassium (K) increased significantly. Soil Na+ and Cl– contents decreased in the PR alone or PR combined with PSB treatment groups. There were strongly synergistic effects of RP and PSB on soil quality, including a decrease in pH. The soil available N, P, and K contents were significantly affected by the PSB treatments. In addition, the alkaline phosphomonoesterases, urease, and dehydrogenase activities increased significantly compared with the untreated group; highest alkaline phosphomonoesterases activity was observed in the RP and PSB treatment groups. The composition of rhizosphere soil bacterial communities was determined using 454-pyrosequencing of the 16S rRNA gene. In the PR alone or PR combined with PSB treatment groups, the structure of the soil bacterial community improved with increasing richness and diversity. With PSB inoculation, the relative abundance of Acidobacteria, Chloroflexi, and Planctomycetes increased. The three phyla were also positively correlated with soil available N and root dry weight. These results suggested microbiological mechanisms by which the combined use of RP and PSB improved saline soil and promoted plant growth. Overall, the study indicates the combined use of RP and PSB can be an economical and sustainable strategy to increase plant growth in P-deficient and salt-affected soils.

Performance of Centrocema grown on mercury-contaminated tailing inoculated with beneficial bacteria: Preliminary study

Low levels of major essential nutrients and high mercury (Hg) content in gold mine tailings can inhibit plant growth. An inexpensive and effective strategy to overcome these obstacles was inoculation of plant-growth promoting bacteria and planting legume cover crops (LCC). A greenhouse experiment was conducted to evaluate the effect of isolates of Nitrogen Fixing Bacteria (NFB) and Phosphate Solubilizing Bacteria (PSB) on some growth characteristics of LCC Censtrosema pubescens (butterfly pea) grown in Hg-contaminated tailing of gold mine tailing. Moreover, the research was aimed to verify the viability of two bacterial groups in tailing after inoculation. The experiment was set up in randomized block design to test single and mixed inoculation of NFB and PSB. The experiment verified that the single inoculation and mixture of two bacteria did not change plant properties compared to the control treatment. Although the statistical analysis was not significant, there were slightly increase in root length as well as NFB and PSB populations of inoculated plants.

Inoculation of phosphate-solubilizing bacteria (Bacillus) regulates microbial interaction to improve phosphorus fractions mobilization during kitchen waste composting

Bacillus presents in most composts as core microbial taxa and is widely used as inoculant in composting. However, the role of Bacillus as phosphate-solubilizing bacteria (PSB) inoculant in composting and the response of indigenous bacterial community are unclear. This study used redundancy analysis (RDA), network analysis and structural equation model (SEM) to investigate the dynamics of phosphorus (P) fractions, bacterial community, and microbial interaction in composting with PSB (Bacillus sp. P6) inoculation. Results indicated that Bacillus inoculation increased Olsen P content, organic matter degradation, and bacterial diversity, benefiting P fractions mobilization during composting. RDA showed that pH was the main factor influencing P fractions transformation and bacterial taxa. Network analysis and SEM revealed that Bacillus indirectly improved the contribution of bacterial community on P mobilization by enhancing microbial interactions. Therefore, Bacillus with P solubilizing function may be a potential inoculant to regulate the biotic process of P transformation.

Is phosphate solubilizing ability in plant growth-promoting rhizobacteria isolated from chickpea linked to their ability to produce ACC deaminase?

Since most phosphate solubilizing bacteria (PSB) also produce 1-aminocyclopropane-1-carboxylate (ACC) deaminase, we investigated if there was an association between these two plant growth-promoting properties under in vitro conditions. A total of 841 bacterial isolates were obtained using selective and enrichment isolation methods. ACC deaminase was investigated using in vitro methods and by sequencing the acdS gene. The effect of ACC deaminase on P solubilization was investigated further using five efficient PSB. ACC deaminase production ability was found amongst a wide range of bacteria belonging to the genera Bacillus, Burkholderia, Pseudomonas and Variovorax. The amount of ACC deaminase produced by PSB was significantly associated with the liberation of Pi from Ca-P when ACC was the sole N source. Ca-P solubilization was associated with the degree of acidification of the medium. Additionally, the P solubilization potential of PSB with (NH4 )2 SO4 was determined by the type of carboxylates produced. An in-planta experiment was conducted using Burkholderia sp. 12F on chickpea cv. Genesis-863 in sand:vermiculite (1:1 v/v) amended with rock phosphate and inoculation of this efficient PSB significantly increased growth, nodulation and P uptake of chickpea fertilized with rock phosphate. ACC deaminase activity influenced the capacity of PSB to solubilize P from Ca-P when ACC was the sole N source and Burkholderia sp. 12F promoted the chickpea-Mesorhizobium symbiosis. ACC deaminase activity could enhance the P solubilizing activity of rhizobacteria that improve plant growth.

Improving the fertilizer value of sugarcane wastes through phosphate rock amendment and phosphate-solubilizing bacteria inoculation

Composting of by-products from the sugarcane (Saccharum spp.) industry can help achieve sustainable biofuel production by replacing mineral fertilizers and adequate residual disposal. The hypothesis was that the compost of filter cake and ash enriched with/without phosphate rocks (apatite-A and phosphorite-P) and phosphate-solubilizing bacteria can replace mineral P fertilizers and improve sugarcane production. A compost was produced from a mixture of filter cake and ash in 60 days of composting. The compost + A and the compost + P (with/without bacteria) were applied at sugarcane planting to supply 150 kg ha−1 P2O5. Yield and quality of sugarcane, soil P dynamics, and enzyme activities in the soil were monitored. Results showed that the application of 20 Mg ha−1 of compost increased sugarcane yield (up to 6%) and β-glucosidase activity (up to 15%) when compared to mineral control. Adding phosphate rock in compost allowed a reduction in the total compost amount from 20 to 10 Mg ha−1, with similar yields. Bacteria inoculation increased sugarcane yield (up to 5%) and acid phosphatase activity (up to 6–18%), enhancing the soil P availability. Compost + P increased labile and moderately labile P contents with a reduction of the acid phosphatase activity. The increase of soluble P (available-P) in the soil is an important gain because most P is fixed (unavailable) in tropical soils. The study revealed a great potential for optimizing by-products generated by the sugarcane industry with the enrichment of compost (adding phosphate rock and phosphate solubilizing bacteria), reducing the dependency of sugarcane production on finite P mineral reserves.

Combination of arbuscular mycorrhizal fungi and phosphate solubilizing bacteria on growth and production of Helianthus tuberosus under field condition

In this work, the effects of co-inoculation between an arbuscular mycorrhizal fungus (AMF) and a phosphate solubilizing bacteria (PSB) to promote the growth and production of sunchoke under field condition were investigated during 2016 and 2017. Four treatments were set up as follows: plants without inoculation, with AMF inoculation, with PSB inoculation and with co-inoculation of PSB and AMF. The results showed the presence of PSB and AMF colonization at the harvest stage in both years. This suggested the survival of PSB and successful AMF colonization throughout the experiments. According to correlation analysis, PSB positively affected AMF spore density and colonization rate. Also, both AMF and PSB positively correlated with growth and production of sunchoke. Co-inoculation could enhance various plant parameters. However, better results in 2016 were found in co-inoculation treatment, while AMF inoculation performed the best in 2017. All of these results suggested that our AMF and PSB could effectively promote growth and production of sunchoke under field conditions. Such effects were varied due to different environmental conditions each year. Note that this is the first study showing successful co-inoculation of AMF and PSB for promoting growth and yield of sunchoke in the real cultivation fields.

Insight into the mechanisms of insoluble phosphate transformation driven by the interactions of compound microbes during composting.

Phosphate-solubilizing (PS) microbes are important to improve phosphorus availability and transformation of insoluble phosphate, e.g., rock phosphate (RP). The use of phosphate solubilizing bacteria (PSB) as inoculants have been proposed as an alternative to increase phosphate availability in RP and composting fertilizers. In this study, the effect of compound PSB coinoculation and single-strain inoculation on the transformation of insoluble phosphate were compared in a liquid medium incubation and RP-enriched composting. The goal of this study was to understand the possible mechanisms of insoluble phosphate transformation driven by the interactions of compound PS microbes during composting. The correlations between organic acids production, P-solubilization capacity and bacterial community with PSB inoculation were investigated in the RP-enriched composting by redundancy analysis (RDA) and structural equation models (SEM). Results showed that both single-strain and compound PSB inoculants had a high P-solubilization capacity in medium, but the proportion of Olsen P to total P in composts with inoculating compound PS microbes was 7% higher than that with single strain. PS inoculants could secrete different organic acids and lactic was the most abundant. However, RDA and SEM suggested that oxalic might play an important role on PS activity, inducing RP solubilization by changing pH during composting. Interaction between compound microbes could intensify the acidolysis process for insoluble P transformation compared to the single strain. Our findings help to understand the roles of complex microbial inoculants and regulate P availability of insoluble phosphate for the agricultural purposes.

Enhanced reduction of lead bioavailability in phosphate mining wasteland soil by a phosphate-solubilizing strain of Pseudomonas sp., LA, coupled with ryegrass (Lolium perenne L.) and sonchus (Sonchus oleraceus L.).

Due to ecologically unsustainable mining strategies, there remain large areas of phosphate mining wasteland contaminated with accumulated lead (Pb). In this study, a Pb-resistant phosphate-solubilizing strain of Pseudomonas sp., LA, isolated from phosphate mining wasteland, was coupled with two species of native plants, ryegrass (Lolium perenne L.) and sonchus (Sonchus oleraceus L.), for use in enhancing the reduction of bioavailable Pb in soil from a phosphate mining wasteland. The effect of PbCO3 solubilization by Pseudomonas sp. strain LA was evaluated in solution culture. It was found that strain LA could attain the best solubilization effect on insoluble Pb when the PbCO3 concentration was 1% (w/v). Pot experiments were carried out to investigate the potential of remediation by ryegrass and sonchus in phosphate mining wastelands with phosphate rock application and phosphate-solubilizing bacteria inoculation. Compared to the control group without strain LA inoculation, the biomass and length of ryegrass and sonchus were markedly increased, available P and Pb in roots increased by 22.2%-325% and 23.3%-368%, respectively, and available P and Pb in above-ground parts increased by 4.44%-388% and 1.67%-303%, respectively, whereas available Pb in soil decreased by 14.1%-27.3%. These results suggest that the combination of strain LA and plants is a bioremediation strategy with considerable potential and could help solve the Pb-contamination problem in phosphate mining wastelands.