Phosphorus Solubilizing Microorganisms Research Articles

Phosphorus Solubilizing Microorganisms: An Eco-Friendly Approach for Sustainable Plant Health and Bioremediation

Phosphorus Solubilizing Microorganisms: An Eco-Friendly Approach for Sustainable Plant Health and Bioremediation

Use of Phosphorus-Solubilizing Microorganisms as a Biotechnological Alternative: A Review.

Microorganisms with the ability to dissolve phosphorus have the potential to release this essential nutrient into the soil through natural solubilization processes, which allows for boosting plant growth and development. While literature reviews acknowledge their potential, unexplored territories concerning accessibility, application, and effective integration into sustainable agriculture necessitate further research. This manuscript employed distinct methodologies to execute a bibliometric analysis and a literature review. The combined application of both methodologies enables a holistic understanding of the domain landscape and its innovative facets. For the bibliometric analysis, the propositions of Donthu and Jia were utilized, supplemented by tools, such as Bibliometrix. The literature review adhered to a systematic methodology predicated on Petersen's guidelines to represent the domain accurately, pinpointing trends and gaps that could steer future, more detailed research. This investigation uncovers an escalating interest in studying these microorganisms since the 2000s, emphasizing their significance in sustainable agriculture and the context of phosphorus scarcity. It was also discerned that India and China, nations with notable agricultural sectors and a high demand for phosphorus fertilizers, spearheaded research output on this subject. This signifies their substantial contribution to the progression of this scientific field. Furthermore, according to the research consulted, phosphorus-solubilizing microorganisms play a pivotal role in the symbiotic interaction of soil with plant roots and represent an efficacious strategy to counteract the low availability of phosphorus in the soil and sustainably enhance agricultural systems. Finally, this review contributes to the relevant domain by examining existing empirical evidence with special emphasis on sustainable agriculture, improved understanding of phosphorus solubilization mechanisms, and recognition of various microbial entities.

Immobilization of Heavy Metals by Phosphorus-solubilizing Bacteria and Inhibition of Cd and Pb Uptake by Wheat

Phosphorus-solubilizing microorganisms convert insoluble phosphorus in the soil into phosphorus that can be absorbed by plants. Soluble phosphate combines with heavy metals to form precipitation, reducing the content of available heavy metals, thereby reducing the absorption of heavy metals by crops, which plays an important role in the remediation of heavy metal-contaminated soil. The effects of the immobilization of Cd and Pb and the release of PO43- by the phosphorus-solubilizing bacterium Klebsiella sp. M2 were studied through solution culture experiments. In addition, the effects of strain M2 on wheat uptake of Cd and Pb and its microbiological mechanism were also explored through pot experiments. The results showed that strain M2 reduced the concentrations of Cd and Pb and increased the concentration of PO43- in the solution through cell wall adsorption and induced phosphate precipitation. Pot experiments showed that compared to those in the CK group and inactivated strain M2 group, inoculation with live strain M2 significantly increased （123%-293%） the contents of Ca2-P and Ca8-P in rhizosphere soil, decreased the content of DTPA-Cd （34.48%） and DTPA-Pb （36.72%） in wheat rhizosphere soil, and thus hindered the accumulation of Cd and Pb in wheat grains. Moreover, high-throughput sequencing results showed that strain M2 significantly increased the diversity of wheat rhizosphere bacterial communities； increased the relative abundance of Proteobacteria, Gemmatimonadetes, and Bacteroidota in wheat rhizosphere soil； and increased the proportion of heavy metal-immobilizing and phosphorus-promoting bacteria in wheat rhizosphere soil （mainly Sphingomonas, Nocardioides, Bacillus, Gemmatimonas, and Enterobacter）. These bacterial genera played an important role in immobilizing heavy metals and preventing wheat from absorbing heavy metals. These results provide bacterial resources and theoretical basis for the bioremediation of heavy metal-contaminated farmland.

Soil chemical fumigation alters soil phosphorus cycling: effects and potential mechanisms

Soil chemical fumigation is an effective and popular method to increase agricultural productivity. However, the broad-spectrum bioactivity of fumigants causes harm to soil beneficial microorganisms involved in the soil phosphorous cycle, such as soil phosphorus solubilizing microorganisms (PSMs). We review the effects of soil chemical fumigation on soil phosphorus cycling, and the potential underlying mechanisms that ultimately lead to altered phosphorus availability for crops. These complex processes involve the highly diverse PSM community and a plethora of soil phosphorus forms. We discuss phosphatizing amendments aimed at counteracting the possible negative effects of fumigation on phosphorus availability, phosphorus use efficiency, and crop yields. We also emphasize distinguishing between the effects on soil phosphorus cycling caused by the chemical fumigants, and those caused by the fumigation process (e.g. plastic mulching). These are typically conflated in the literature; distinguishing them is critical for identifying appropriate amendments to remediate possible post-fumigation soil phosphorus deficiencies.

Effect of Phosphate Rock Powder, Active Minerals, and Phosphorus Solubilizing Microorganisms on the Phosphorus Release Characteristics of Soils in Coal Mining Subsidence Areas

Effect of Phosphate Rock Powder, Active Minerals, and Phosphorus Solubilizing Microorganisms on the Phosphorus Release Characteristics of Soils in Coal Mining Subsidence Areas

Genomics analysis of three phosphorus-dissolving bacteria isolated from Torreya grandis soil.

With the increasingly serious problem of phosphorus deficiency in the subtropical zone, chemical fertilizers are widely used. But it pollutes the environment. Phosphorus-solubilizing microorganisms (PSMs) are referred to as a new solution to this problem. We explored the phosphorus-dissolving characteristics of PSB strains isolated from the rhizosphere soil of Torreya grandis to provide a theoretical basis for selecting the strain for managing phosphorus deficiency in subtropical soils and also provides a more sufficient theoretical basis for the utilization of PSMs. From 84 strains, three strains exhibiting high phosphorus solubility and strong IAA producing capacity were selected through a series of experiments. The phosphate-solubilizing capacity of the three selected strains W1, W74, and W83 were 339.78mg/L, 332.57mg/L, and 358.61mg/L, respectively. Furthermore, W1 showed the strongest IAA secreting capacity of 8.62mg/L, followed by W74 (7.58mg/L), and W83 (7.59mg/L). Determination by metabolites, it was observed that these three strains dissolved phosphorus by secreting a large amount of lactic acid, aromatic acid, and succinic acid. The genome of these PSBs were sequenced and annotated in this study. Our results revealed that PSB primarily promotes their metabolic pathway, especially carbon metabolism, to secrete plenty organic acids for dissolving insoluble phosphorus.

Effects of Chemical Fertilizer Reduction Substitute with Organic Fertilizer on Soil Functional Microbes and Lemon Yield and Quality

To clarify the effects of non-rhizosphere/rhizosphere soil functional microbes (nitrifiers, denitrifiers, and phosphorus-solubilizing microorganisms) on lemon yield and quality, the lemon fruit and non-rhizosphere/rhizosphere soil were selected as subjects. To explore the correlation between non-rhizosphere/rhizosphere soil functional microbes and lemon yield and quality under a chemical fertilizer reduction substitute with organic fertilizer, traditional fruit quality determination and multiple molecular techniques were used. The results showed that:① 30% chemical fertilizer reduction substitute with organic fertilizer increased the nitrification intensity and phosphatase activity but effectively controlled the denitrifying enzyme activity. ② The chemical fertilizer reduction substitute with organic fertilizer significantly decreased the abundances of nitrifiers and nirS/nirK-harboring denitrifiers and significantly increased the abundances of nosZ-harboring denitrifier and phoD-harboring microorganisms. However, the diversities of functional microbial community structure did not have clear regularity under chemical fertilizer reduction substitute with organic fertilizer. ③ Compared with that under the application of chemical fertilizer and organic fertilizer alone, lemon yield and quality were the highest under the 30% reduction of chemical fertilizer substitute with organic fertilizer. ④ Nitrogen and its related microbes significantly affected lemon yield through internal and external quality. Phosphorus and its related microbes affected lemon yield mainly through internal quality. In addition, the influence factors of non-rhizosphere soil and rhizosphere soil on lemon intrinsic quality were obviously different. Altogether, these results showed that the 30% reduction of chemical fertilizer substitute with organic fertilizer significantly affected soil nitrogen and phosphorus functional microorganisms and further improved lemon yield and quality.

Biochar: An effective measure to strengthen phosphorus solubilizing microorganisms for remediation of heavy metal pollution in soil.

OPINION article Front. Bioeng. Biotechnol., 02 March 2023Sec. Bioprocess Engineering Volume 11 - 2023 | https://doi.org/10.3389/fbioe.2023.1127166

Phosphate-Solubilizing Capacity of Paecilomyces lilacinus PSF7 and Optimization Using Response Surface Methodology.

Phosphorus-solubilizing microorganisms release organic acids that can chelate mineral ions or reduce the pH to solubilize insoluble phosphates for use by plants; it is important to study potential phosphorus-solubilizing microorganisms for use in agriculture. In this study, PSF7 was isolated from the soil of the Wengfu Phosphorus Tailings Dump in Fuquan City, Guizhou Province, China. PSF7 was identified as Paecilomyces lilacinus, based on morphological characterization and ITS sequencing analysis. The relationship between the phosphorus-solubilizing capacity and pH variation of PSF7 under liquid fermentation was studied. The results showed that there was a significant negative correlation (-0.784) between the soluble phosphorus content of PSF7 and the pH value. When PSF7 was placed under low phosphorus stress, eight organic acids were determined from fermentation broth using HPLC, of which tartaric acid and formic acid were the main organic acids. Different optimization parameters of medium components were analyzed using response surface methodology. The optimized medium components were 23.50 g/L sucrose, 1.64 g/L ammonium sulfate and soybean residue, 1.07 g/L inorganic salts, and 9.16 g/L tricalcium phosphate, with a predicted soluble phosphorus content of 123.89 mg/L. Under the optimum medium composition, the actual phosphorus-solubilizing content of PSF7 reached 122.17 mg/L. Moreover, scanning electron microscopy analysis of the sample was carried out to characterize the phosphate-solubilizing efficiency of PSF7 on mineral phosphate. The results provide useful information for the future application of PSF7 as a biological fertilizer.

Changes in Soil Phosphorus Availability and Microbial Community Structures in Rhizospheres of Oilseed Rapes Induced by Intercropping with White Lupins

Oilseed rape is sensitive to soil phosphorus deficiencies. In contrast, white lupin is widely used as a model plant because it has efficient phosphorus utilization. Therefore, soil fertility and microbial composition in the rhizospheres of oilseed rapes and root exudate metabolites were compared under monocropping and intercropping systems. The main purpose was to explore whether the phosphorus absorption of rapeseed can be promoted by intercropping with white lupine. In comparison with oilseed rape monoculture (RR), the results showed that the contents of soil-available phosphorus, microbial biomass and phosphorus in the rhizospheres of oilseed rapes in the intercropping system (RL) were all higher than those of RR. Meanwhile, in comparison with RR, not only phosphorus-solubilizing bacteria, such as Streptomyces, Actinomadura and Bacillus, but also phosphorus-solubilizing fungi, such as Chaetomium, Aspergillus, Penicillium, were enriched in the rhizospheres of the oilseed rape under the RL system. Moreover, more abundant soil bacterial functions, organic acids and metabolites were also detected in root exudates of the oilseed rapes under the RL system. All of the above results suggest that soil phosphorus availability in the rhizospheres of oilseed rape could be improved by intercropping with white lupin. Additionally, soil phosphorus-solubilizing microorganisms, that are enriched in the rhizospheres of oilseed rapes under RL systems, have an important function in the improvement of phosphorus absorption of rapeseed by intercropping with white lupin.

Influence of Aspergillus niger Phospho-compost on Growth, Dry Matter Yield and P Uptake of Maize

Aims: Soils in Ghana's coastal savanna are typically poor in phosphorus (P), which has an impact on crop growth and productivity. The majority of West African phosphate rock formations are not reactive; therefore, their direct applications do not facilitate easy P availability to crops. Co-composting organic waste with phosphate rock and using phosphorus-solubilizing microorganisms is the new paradigm adopted by scientists in response to the lack of P availability (PSMs). The goals of this study were to (1) assess the effect of Aspergillus niger in P dissolution in phosphate rock during composting with citrus waste (CW) and rice straw (RS) and (2) to evaluate the effect of phosphor-compost on growth, dry matter yield and P uptake of maize.
 Methodology: Preparation of compost took place at University of Ghana Forest and Horticulture Research Center, Okumaning Camp close to Kade. Citrus waste and rice straw were used as feed stock. Each composting pile contained a mixture of urea, Togo phosphate rock, and feedstock in a 1:3:24 weight-to-weight ratio.
 Results: According to the findings, citrus waste feedstock was superior to rice straw in dissolving the P in rock phosphate. In a pot experiment, the phospho-composts were assessed using maize (Zea mays) as the test crop.

Distinct Patterns of Rhizosphere Microbiota Associated With Rice Genotypes Differing in Aluminum Tolerance in an Acid Sulfate Soil.

Rhizosphere microbes are important for plant tolerance to various soil stresses. Rice is the most aluminum (Al)-tolerant small grain cereal crop species, but the link between rice Al tolerance and rhizosphere microbiota remains unclear. This study aimed to investigate the microbial community structure of aluminum-sensitive and Al-tolerant rice varieties in acid sulfate soil under liming and non-liming conditions. We analyzed the rice biomass and mineral element contents of rice plants as well as the chemical properties and microbial (archaea, bacteria, and fungi) communities of rhizosphere and bulk soil samples. The results showed that the Al-tolerant rice genotype grew better and was able to take up more phosphorus from the acid sulfate soil than the Al-sensitive genotype. Liming was the main factor altering the microbial diversity and community structure, followed by rhizosphere effects. In the absence of liming effects, the rice genotypes shifted the community structure of bacteria and fungi, which accounted for the observed variation in the rice biomass. The Al-tolerant rice genotype recruited specific bacterial and fungal taxa (Bacillus, Pseudomonas, Aspergillus, and Rhizopus) associated with phosphorus solubilization and plant growth promotion. The soil microbial co-occurrence network of the Al-tolerant rice genotype was more complex than that of the Al-sensitive rice genotype. In conclusion, the bacterial and fungal community in the rhizosphere has genotype-dependent effects on rice Al tolerance. Aluminum-tolerant rice genotypes recruit specific microbial taxa, especially phosphorus-solubilizing microorganisms, and are associated with complex microbial co-occurrence networks, which may enhance rice growth in acid sulfate soil.

Glucose Increases the Abundance of Phosphate Solubilizing Bacterial Community for Better Apple Seedling Growth and Phosphate Uptake

Phosphorus-solubilizing microorganisms play an important role in soil nutrient phosphorus cycling. In order to clarify the effect of glucose (C6H12O6) on soil phosphorus transformation, the effects of glucose additions on the bacterial community, soil phosphorus status, and plant phosphorus uptake in apple rhizosphere soil were investigated. A 90-day pot experiment was carried out, and the experiment was repeated three times. Glucose additions were 0, 2.5, 5, 7.5, 10, and 12.5 g glucose per kg of soil. We measured soil bacteria and phosphorus related indexes using Illumina MiSeq sequencing technology and chemical methods. The results showed that when the glucose application rate was 2.5–7.5 g·kg−1, the soil total phosphorus content decreased by 4.4–7.3%; however, the soil acid phosphatase activity increased by 0.5–1.3 times, and the microbial biomass phosphorus increased by 29.1% and 37.0%. The content of Al-P and Fe-P in the rhizosphere soil decreased by 14.4 to 32.7 mg·kg−1 and 16.04 to 28.7 mg·kg−1, respectively. The compositional difference of the bacterial community became larger, and the relative abundance of 11 bacterial phyla changed significantly, among which the most significant change was found in Proteobacteria. This study also found that the relative abundances of Bacillus, Pseudomonas, Arthrobacter, and Cuprococcus increased by 0.9%, 2.2%, 2.4%, and 0.8%, respectively. Applying 7.5 g glucose per kg of soil can significantly increase the relative abundance of phosphorus solubilizing bacteria (Bacillus, Pseudomonas, Arthrobacter et al.) in rhizosphere soil, activate Al-P and Fe-P, and improve the availability of soil phosphorus.

Vermicompost Amended With Rock Phosphate as a Climate Smart Technology for Production of Organic Swiss Chard (Beta vulgaris subsp. vulgaris)

Vermicomposting is being promoted as climate-smart agriculture (CSA) technology for developing organic nutrient sources that can be adopted by smallholder farmers. The amendment of soils with cost-effective and available inorganic fertilizers like rock phosphate (RP) and phosphorus-solubilizing microorganisms should also be promoted. Our study investigated the seedling and maturity growth of Swiss chard. The crop maturity study investigated the effect of amending an Oxisol soil with three phosphorus (P) sources applied at three different rates (0, 25, and 50 mg P kg−1 soil), cow and pig manures, and P-solubilizing bacteria resulting in the following treatments: control (soil), soil + RP alone, soil + RP-enriched cow manure vermicompost (VC) with phosphorus-solubilizing bacteria (PSB), and soil + RP-enriched pig manure vermicompost (VP) with PSB. The study investigated the growth performance and accumulation of copper (Cu), zinc (Zn), chromium (Cr), and lead (Pb) in the edible parts of Swiss chard (Beta vulgaris subsp. valgaris var. Cicla). The seedlings were grown using pine bark compost and the three P sources (VC, VP, and RP) at five different application rates (0, 25, 50, 75, and 100%). The results revealed that the use of 50 mg P kg−1 as VP gave the highest fresh weight of 39.78 g, leaf area of 240.41 cm2, and a total P in tissues of 326.91 mg kg−1 at 8 weeks after transplanting. The 50 mg P kg−1 application as VC resulted in a higher Zn content of 8.50 mg kg−1, which was above the permissible level. These results suggest that the best treatment mixture for establishing fully matured Swiss chard was the 50 mg P kg−1 as VP. Therefore, pig manure vermicompost that has been inoculated with phosphorus-solubilizing microorganisms is a promising CSA technology that can improve organic vegetable production by smallholder farmers.

Screening and activity assessing of phosphorus availability improving microorganisms associated with bamboo rhizosphere in subtropical China.

Phosphorus-solubilizing microorganisms (PSMicros) play vital roles in helping plants to resist phosphorus (P) deficiency in soils, while their activities may vary with site conditions. The present study investigated the microbial diversity and subsequently screened PSMicro strains from rhizosphere soils at five bamboo forests in subtropical China, among which four were developed in a same stand. The activities of the screened PSMicros were also assessed. The results showed great variation in microbial diversity among different forests. Concomitantly, a total of 52 PSMicro strains were isolated and identified to 10 bacterial genera and 4 fungal genera, with different forest rhizosphere soils containing different PSMicros and/or showing different abundances for a certain PSMicro genus, despite some PSMicros would not grow readily on plates. Different, and even the same microbial genera isolated across the five forests, varied significantly in the amount of P that they solubilized from the medium, which ranged from 18.5 to 581.33 mg L-1 . Among the isolated PSMicros, species of Bacillus, Kluyvera, Buttiauxella, Meyerozyma and Penicillium were preponderant to liberate P from organic and inorganic P pools. This will have implications for biotechnological exploitation of microbes to alleviate P limitation in agricultural and natural systems with a sustainable green ecological approach.

Isolation and screening of multifunctional phosphate solubilizing bacteria and its growth-promoting effect on Chinese fir seedlings

Phosphorus-solubilizing microorganisms is a microbial fertilizer with broad application potential. In this study, 7 endophytic phosphate solubilizing bacteria were screened out from Chinese fir, and were characterized for plant growth-promoting traits. Based on morphological and 16S rRNA sequence analysis, the endophytes were distributed into 5 genera of which belong to Pseudomonas, Burkholderia, Paraburkholderia, Novosphingobium, and Ochrobactrum. HRP2, SSP2 and JRP22 were selected based on their plant growth-promoting traits for evaluation of Chinese fir growth enhancement. The growth parameters of Chinese fir seedlings after inoculation were significantly greater than those of the uninoculated control group. The results showed that PSBs HRP2, SSP2 and JRP22 increased plant height (up to 1.26 times), stem diameter (up to 40.69%) and the biomass of roots, stems and leaves (up to 21.28%, 29.09% and 20.78%) compared to the control. Total N (TN), total P (TP), total K (TK), Mg and Fe contents in leaf were positively affected by PSBs while showed a significant relationship with strain and dilution ratio. The content of TN, TP, TK, available phosphorus (AP) and available potassium (AK) in the soil increased by 0.23–1.12 mg g−1, 0.14–0.26 mg g−1, 0.33–1.92 mg g−1, 5.31–20.56 mg kg−1, 15.37–54.68 mg kg−1, respectively. Treatment with both HRP2, SSP2 and JRP22 increased leaf and root biomass as well as their N, P, K uptake by affecting soil urease and acid phosphatase activities, and the content of available nutrients in soil. In conclusion, PSB could be used as biological agents instead of chemical fertilizers for agroforestry production to reduce environmental pollution and increase the yield of Chinese fir.

Soil Type Affects Organic Acid Production and Phosphorus Solubilization Efficiency Mediated by Several Native Fungal Strains from Mexico.

Phosphorus (P) is considered a scarce macronutrient for plants in most tropical soils. The application of rock phosphate (RP) has been used to fertilize crops, but the amount of P released is not always at a necessary level for the plant. An alternative to this problem is the use of Phosphorus Solubilizing Microorganisms (PSM) to release P from chemically unavailable forms. This study compared the P sorption capacity of soils (the ability to retain P, making it unavailable for the plant) and the profile of organic acids (OA) produced by fungal isolates and the in vitro solubilization efficiency of RP. Trichoderma and Aspergillus strains were assessed in media with or without RP and different soils (Andisol, Alfisol, Vertisol). The type and amount of OA and the amount of soluble P were quantified, and according to our data, under the conditions tested, significant differences were observed in the OA profiles and the amount of soluble P present in the different soils. The efficiency to solubilize RP lies in the release of OAs with low acidity constants independent of the concentration at which they are released. It is proposed that the main mechanism of RP dissolution is the production of OAs.

Effect of Arbuscular Mycorrhizal Fungi and Phosphate-Solubilizing Bacteria Consortia Associated with Phospho-Compost on Phosphorus Solubilization and Growth of Tomato Seedlings (Solanum lycopersicum L.)

ABSTRACTThe exploitation of phosphate mines generates an important quantity of phosphate sludge that remains accumulated and not valorized. In this context, composting with organic matter and rhizospheric microorganisms offers an interesting alternative and that is more sustainable for agriculture. This work aims to investigate the synergetic effect of arbuscular mycorrhizal fungi (AMF), phosphate-solubilizing bacteria (PSB) and phospho-compost (PC), produced from phosphate-laundered sludge and organic wastes, and their combination on plant growth, phosphorus solubilization and phosphatase activities (alkaline and acid). Inoculated mycorrhizae and bacteria strains used in this study were selected from plant rhizosphere grown on phosphate-laundered sludge. Significant (p < .05) increases in plant growth was observed when inoculated with both consortia and PC (PC+ PSB+ AMF) similar to those recorded in plants amended with chemical fertilizer. Tripartite inoculated tomato had a significantly (p < .05) higher shoot height; shoot and root dry weight, root colonization and available P content, than the control. Co-inoculation with PC and AMF greatly increased alkaline phosphatase activity and the rate of mycorrhizal intensity. We conclude that PC and endophytic AMF and PSB consortia contribute to a tripartite inoculation in tomato seedlings and are coordinately involved in plant growth and phosphorus solubilization. These results open up promising prospects for using formulate phospho-compost enriched with phosphorus-solubilizing microorganisms (PSM) in crop cultivation as biofertilizers to solve problems of phosphate-laundered sludge accumulation.

Hiện trạng hệ vi sinh vật phân giải lân trên một số loại đất phù sa trồng lúa nước vùng đồng bằng sông Hồng

The aim of this study was to assess phosphorus solubilizing microorganisms in eutric fluvisols (Gia Lam district, Hanoi) and gleyic fluvisols (Tien Lu district, Hung Yen province) for cultivating rice in the Red River Delta (2 crops per year). The results of isolation showed the appearance of bacteria, actinomycetes in the samples, but absence of fungi. Overall, density of phosphorus solubilizing microorganisms in eutric fluvisols was much more than that in gleyic fluvisols; however, the amount of strains was less diverse. It was not the same between the 2 types of soil, even between different samples of the same soil type. There were 4 common strains of bacteria in eutric fluvisols; the density ranged from 15.5 to 22.9 x104 CFU/g soil. Meanwhile, the gleyic fluvisols had 4 strains of popular bacteria and 1 strains of actinomycetes, ranged from 2.3 to 17.3 x104 CFU/g soil. In these 2 soil types, the density of inorganic-phosphate solubilizing microorganism was higher than that of organic- phosphate solubilizing microorganism. However, compared to the total of microorganisms, both microbial groups were very low in density, less than 1% of each. Besides, ability of phosphorus solubilization of them are not high, phosphate PO43- released ranging from 0.70 to 5.66 ppm (Tricalcium phosphate form) and from 0.0 to 1.83 ppm (Lecithine form).

Phosphate-solubilizing microbes in rhizosphere soils of 19 weeds in southeastern China

Low phosphorus (P) availability is one of the most important factors limiting plant growth in red soils across southeastern China. Many non-symbiotic microorganisms in rhizosphere can enhance P solubility, but little is known about the magnitude of their phosphorus-solubilizing ability (PSA) and the difference in phosphorus-solubilizing microorganisms (PSM) among plant species. The number of phosphorus-solubilizing microorganisms and their PSA in rhizosphere soils of 19 weed species in a citrus orchard on red soil at Changshan. Zhejiang. China, were investigated. Inorganic P (powdered phosphate rock, PR) and organic P (lecithin, OP) were respectively used as the sole P-source to examine the PSA of isolated microbes. The PS actinomycetes community varied greatly among the different weed rhizospheres while the PS fungus community showed to be most stable to the weed rhizosphere. The highest number of PR-PS and OP-PS bacteria was found in rhizosphere soil of Mollugo pentaphyll, and the highest number of PR-PS and OP-PS actinomycetes was found in rhizosphere soil of Polygonum lapathifolium. The highest number of PR-PS fungi was found in Erigeron annuus and Mollugo pentaphyll rhizosphere soil, and the highest number of OP-PS fungi was found in rhizosphere soil of Mazus stachydifolius. Mazus stachydifolius showed the strongest PR-PS ability (6340.75/μg) while Eragrostis pilosa showed the strongest OP-PS ability (1301. 84/μg). The PR-PS ability and OP-PS ability of Mollugo pentaphyll was 4432.87μg and 1122.05μg respectively. A significant correlation between the number of PR-PSM and OP-PSM was found. Significant correlation was only found between the PR-PS fungi number and its PSA (r = 0.75, P<05) and between the number of OP-PS fungi and its PSA (r = 0.87, P<0.01}). It indicated that plant species had significant influence on components of the non symbiotic PSM community and their activity in its rhizosphere soil. Fungi play a leading role in phosphorus solubilization in weed rhizopshere. It suggested that weed conservation could benefit soil microbe development in agroecosystems, especially in the initial stage of agroecosystem development because there is less organic carbon in bare soil. The results suggested that weed conservation could increase PSA of PSM.