Plants procure phosphorus from soil as the phosphate anion. It is the most un-portable component in plant and soil in comparison to other macronutrients. It’s very well known that phosphorus is the second most significant supplement after the nitrogen required/needed in plant growth. It is a fundamental component in every single living system. Barely 1%-2% of phosphorous is provided to different parts of the plants. It precipitates in soil as orthophosphate or is adsorbed by Fe and Al oxides through legend exchange.

Phosphorus-solubilizing bacteria play a substantial part in phosphorus nutrition by increasing phosphorus' accessibility to plants through discharge from inorganic and natural soil P pools by solubilization and mineralization. Lowering the pH of the soil through microbial generation of natural acids and mineralization of natural phosphorus by acid phosphates is the key element in the soil for mineral phosphate solubilization. Chemical composts are used as an additional source of phosphorous to satisfy the plant’s need. Additionally, co-inoculating P solubilizing microorganisms with other beneficial bacteria and mycorrhiza has shown to increase their efficiency. Microbial inoculants or biofertilizers can thus be used as an alternative source because they are both economical and environmentally favourable.

Keywords: phosphorous, manure, vegetables, nutrition, soil, microorganisms

Despite its excess in both organic and inorganic soil structures, phosphorus (P) plays a vital role in plant development and is the major supplement that restricts plant growth.¹ The main features of phosphorous nourishment are Metabolic cycles as- photosynthesis, energy move and signal transduction and assurance from plant ailments, Nitrogen obsession in vegetables, crop quality.^2,3 Plants consume it in the form of orthophosphate (H₂PO₄-and HPO₄ 2-).⁴ Grains collect a significant portion of the phosphorus that plants use as phytase⁵ and its inadequacy influences the grains yield very badly and make the unfavorable impact on crops. Stem and stalk strength, blossom, root development, seed arrangement, yield development and production, nitrogen-fixation in vegetables, crop quality, and protection from plant diseases are a few characteristics that are related to phosphorus nutrition. Since microbial inoculants have been utilized to increase soil fertility for the past 100 years, studies has been conducted on Phosphorous solubilization in contrast with the N- fixation. In soil, phosphorus elements are primarily defined by natural (immobilization-mineralization) and physicochemical processes (sorption-desorption). Massive amounts of phosphorus are added as manure, and through precipitation, it reaches stable pools with exceptionally receptive Ca2+ in calcareous water and Fe3+ and Al3+ in acidic water.^1,6,7 The phosphorus elements in the soil are greatly influenced by soil microorganisms, which makes phosphate available to plants.⁸

Phosphorus solubilizing microorganisms

As compared to the parasite, the bacteria are more effective in phosphorus solubilization.⁹ In Phosphorous solubilization potential the phosphorus solubilizing fungi (PSF) are simply 0.1 to 0.5 % whereas the PSB comprise of 1 to 50 % in the entire microbial populace in soil.¹⁰ Microorganisms associated with phosphorus securing incorporate mycorrhizal growths and PSMs.¹¹ From the bacterial community of soil ectorhizospheric strains have been depicted from the Pseudomonas and Bacilli whereas the endosymbiotic rhizobia have been depicted as a strong P solubilizers.¹² The most remarkable P solubilizers are the fungi - Penicillium and Aspergillus along with strains of bacterial enera- Rhizobium, Bacillus, Pseudomonas and Enterobacter.¹³ According to Subbarao;¹⁴ Kucey et al.,¹⁵ the B. subtilis, B. polymyxa, Bacillus megaterium, B. sircalmous, B. circulans, and Pseudomonas striata could be considered as main strains. For the solubilization of phosphate rocks a nematofungus called as Arthrobotrys oligospora is considered as the most.¹⁶

Mechanism of action of phosphorus solubilizing microorganisms

According to Ahmed and Hamid,¹⁷ the efficiency of P compost worldwide ranges from 10 to 25%, and the exceptionally low bioavailable content of P in soil (1.0mg kg-1) is quite low.⁷ Plants can absorb phosphorus only in soluble form. The phosphorus (P) elements in the soil are greatly influenced by soil microbes, which make phosphate available to plants.⁵ The Phosphate Solubilizing Microorganisms, specifically Phosphate Solubilizing Bacteria, improve the solubilization of a mixture of insoluble phosphorous by the influx of phosphatase, natural acids, and phytase complexes¹⁸ and this is mostly accessible in a wide assortment of the soil microorganisms. Sclerotium, Penicillium, and Aspergillus are three examples of species that are dynamic in change. Micrococcus, Mycobacterium, Pseudomonas, and Flavobacterium are four bacteria species that are also dynamic in change. While some phosphorous is consumed by microbes during the transformation cycle, the total amount is first rendered soluble and then provided in excess to the microorganisms' needs. As a result, the extra phosphorus is subsequently transported and made available to the plants. Natural acid plays a big part in this transition process. Similar to how nitric acid does, sulfuric acid also plays significant role in it. Thus, through these natural and inorganic acids, calcium phosphate is then converted to di or monobasic phosphates and is thereafter efficiently available to the plants.^10,18–20 Because the sulphuric and nitric acids are delivered by oxidation of the nitrogenous materials, acts on the rock phosphate, the carbohydrates that are being oxidized by the heterotrophs have an enormous impact upon the solubilization interaction.²¹ During this process by the nitrification of ammonium salts a huge impact was observed in the solubilization of phosphate. By and large, by the production of acid the solubilization of phosphate is accomplished.²² Preparation of ferric phosphate requires specific microscopic organisms which liberates the hydrogen sulfide. Various phosphate solubilizing microorganisms are furthermore well known in soil. It is furthermore understood that root area is amply affluent in phosphate solubilizing microorganisms. Because of this, process of the phosphate osmosis by the advanced plants increases rapidly. The soil fertility increases up to a moderate degree through v the mycorrhizal organism.²³ Also the numerous microbes, growths, and the actinomycetes discharge bound P in yield deposits and the organic soil matter which is eventually accessible for pSlants. Likewise, hemophilic and mesophilic microscopic organisms' effectively take part in the mineralization of phosphorus.¹⁸ Warm temperature ordinarily leans toward deterioration and because of this thermophilic species play a significant role.²⁴ PH of soil also plays a significant role in it.²⁵ Similar to the nitrogen, phosphorous is also mineralized as well as immobilized in soil. These both cycle work in the soil and are administered by how much phosphorus deposits in the plant going through deterioration and the supplements is expected for related population of microbes. Phosphate is formulated when the proportion limits with period on account of the CO₂ volatization (Table 1).

It is intriguing to speculate that PSM could influence plant growth and nutritional requirements through their component of activity. The capacity of plant growth hormones to create phosphate makes it clear that these phosphate-stimulating microorganisms could be used as a successful substitute for inorganic phosphate composts in the future and should be utilised more frequently. However, P solubilizing inoculants can enhance microbial activity, which may significantly improve in P uptake by the plants. Phosphorus solubilizing microorganisms (PSM) including Pseudomonas, Bacillus, and Enterobacter are very effective at enhancing the amount of P that plants can access for growth and productivity. In this respect, the use of phosphate solubilizing microorganisms (PSM) in bio-fertilization offers enormous potential for utilising fixed P in the soil. Along with this it also enhance the natural stocks of phosphate rocks.

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The authors declared that there is no conflict of interest.

None.

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