.A sustainable approach for improving soil fertility and health is focused on the use of natural resources and soil biodiversity. There are different types of soil organisms playing a direct role in the overall growth and development of plants. Notably, these microbial groups can all have other PGP traits, such as phytohormones and siderophores, amino acids, polysaccharides, and amino acids, and thereby conceivably contribute to crop improvement.
Silva et al., 2020 experimented to check the beneficial effects of soil microorganisms on growth and yield-related factors of soybean.
The treatments for this experiment consisted of Serratia sp., Azospirillum sp., Azospirillum brasilense, Burkholderia sp., Pseudomonas sp. And fungus Trichoderma asperellum. Results of the study have shown that all treatments include the application of soil microorganisms. As in isolation or combination greatly improved all growth and yield-related parameters.
Sustainable Approach to Use Plant Root Exudates to Support Soil Microorganisms
Because soil microbes grow in a carbon-restricted environment, the rich amounts of sugars and amino acids that plants accumulate into their rhizospheres provide a beneficial source of nutrition. Accumulation of this labile material does not encourage the proper use of beneficial microbes and soil bacteria. However, pathogenic strains may also use these molecules as valuable growth substrates.
Plant Breeding Strategies for Targeted Secretion of Root Exudates
Studying the microbiome of various plant species and successions led to strong differences, which suggests that exudates are critical in shaping plant-microbe interactions.
Root-derived signals are also known to attract beneficial interactions partners. Rhizodeposition refers to the total release of fixed carbon compounds (exudates and border cells) into the surrounding soil. These exudates differ in composition between species. Pea exudates have high levels of organic acids while oil radish exudates have high levels of sugars.
Plant Species Richness and Root Exudates
Eisenhauer et al., 2017 experimented to check the role of the richness of plants. Species on soil bacteria, soil fungi, and soil bacterial to fungal ratio via root exudates and root biomass. They used a microcosm experiment for investigating the effects of diverse plant species on the biomass of soil fungi, and soil bacteria.
Root biomass of different species was determined by using quantitative PCR and the quantity and diversity of root exudates were studied by high-pressure liquid chromatography (HPLC). Results of the findings have revealed a significant correlation between root and shoot. Biomass, plant production, species diversity, and root exudates.
Arbuscular Mycorrhizal Fungi (AMF) and Phosphate Solubilizing Biofertilizers
AMF, in addition to PSM, is a key component of agricultural systems. These are the most common microbial components of agricultural systems (concerns over 80% of terrestrial and vascular plants). This is defined as a symbiotic relationship that involves a two-directional exchange between two organisms. They could contribute up to 80% to the total P uptake of phosphate in soil depending on the soil type and treatment.
AMF is morphologically a part of the rooting network and acts as an extension of it. This allows the plants to search for nutrients well beyond the boundaries of the rhizosphere. AMF acts as an extra pathway for P uptake (AMF pathway), with arbuscular acting as the symbiosis interconnect. This allows plants to scavenge nutrients and organic phosphate far beyond the boundaries of the rooting system.
AMF hyphae are smaller than roots, they have a high affinity to inorganic phosphates and phosphorus chelate. They can also explore soil pores inaccessible to them and increase the translocation of that inorganic phosphorous. The polyphosphates are then transported through the vacuole to intra-radical and cleaved hyphae. Moreover, the use of phosphate solubilizing bacteria is also important to improve phosphorus uptake and accumulation in plants.
What are phosphates used for
It seems that plants have evolved specific P transporters, which have been recognized for different species such as tomato, potato, and barely. Although fungal hyphae are capable of exuding organic acids and acid phosphatase enzymes, it is not clear how AMF can increase P phosphate and P availability. AMF may be involved in P solubilization via a synergic relationship to PGPM, according to a consensus.
Hou et al., 2021 experimented to improve phosphorus uptake in maize plants under high plantation density conditions in China. They applied mesh barrier compartments for monitoring the hyphal phosphorus uptake distribution throughout growing periods in different soil depths and planting densities for two consecutive years.
The results of the study have revealed that AMF application significantly improved the phosphorus acquisition efficiency of the plants, especially during silking stages. Results have also suggested that AMF applications can eliminate the requirements for phosphorus fertilizers to improve phosphorus in soil for the maintenance of higher crop yields.
Sustainable Approach to Use Phosphate Solubilizing Microorganisms (PSM)
There are many genera of bacteria, including Pseudomonas and Bacillus, Azotobacter and Brady rhizobium, as well as fungi (e.g., Penicillium, Aspergillus, and Streptomyces), that can solubilize Phoshorus metal complexes for releasing bioavailable P. This is done all the way through certain mechanisms. These include organic acids, siderophore, and phosphatase enzymes which play a crucial role in the hydrolysis of organic P forms.
PSM could promote plant growth by increasing phosphorus use efficiencies through exudation and phosphorus hydrolyzing Phosphatase enzymes. Results of various scientific studies have revealed that PSM is a significantly important bio fertilizer examples and helps to improve production on a sustainable basis.
Beneficial microorganisms are the main contributors to P solubilization. However, this process is mostly gene-dependent. Ecosystem environmental properties could influence organic acid production. N and C soil can create impacts on the quality of produced organic acids by the application of bacterial fertilizers.
The nature of C sources could also affect the bio-solubilization process. A high ratio of C/P appears to increase organic acid production, while both C/N and N/P can affect the development of microorganisms. Important to remember that P solubilization effectiveness is dependent more on the quality than on the number of organic acids or P sources.
PSM can produce many organic acids, including acetic acid, gluconic, glucuronic, butyric, butyric, fumaric, and valeric acids. The most common are 2-ketoglutonic and gluconic acids in gram-negative bacteria. The reduction of pH and cations-chelating properties are often the reason for organic acid involvement in P solubilization. Acidification of the microbial cells’ boundary results in the release of phosphorus anion through substitution of H+ or Ca2+.
There may be other mechanisms behind this phenomenon such as the protons released from ammonium assimilation cells by microbial cells, and the production of certain inorganic acids (i.e., sulfuric and nitric acid), and the particular enzymes that act on amphiphilic fat substances are all possible.
Elhaissoufi et al., 2020 experimented to investigate the below ground and above. Ground responses of phosphorus solubilizing isolates in the wheat crop specifically fertilized with the rock phosphate under the controlled conditions. Researchers isolated the DNA for molecular investigations and taxonomic identification of phosphorus solubilizing isolates.
All the isolates were carefully studied for phosphorus solubility potential. Additionally, they also studied plant growth-promoting traits of these isolates and the results. Studies have reported that the application of phosphate solubilizing bacteria greatly improved. The nutrient uptake, chlorophyll contents, protein contents, and the activity of acid phosphatase in the wheat roots.
Sustainable Approach to Use Soil Microorganisms for Biological Nitrogen Fixation
Biological Nitrogen Fixation (BNF) generally, refers to a microbially-facilitated process where atmospheric N2 is converted into ammonia (NH3) by nitrogenase. This enzymatic transformation is performed by a variety of diazotrophs, which are nitrogen fixing bacteria in soil. While some diazotrophs can fix N2 in their free-living status while others do it in association and with plants, together with endophytic bacteria (inside plant tissues) or symbiotic bacteria.
These include fundamental and functional modifications that both microbes and roots undergo in specialized structures called nodules.
Sustainable Approach to Use Bacteria as biofertilizer
These bacteria can use root nodules for sequestering atmospheric N as ammonia. This form of N can later be used to make organic components such as proteins, nucleic acid, and nucleic acid. Symbiotic nitrogen fixation (symbiotic N) involves the net transfering of biologically fixed nitrogen from the bacteria directly to the host plant.
Non-symbiotic bacteria can proliferate due to nutrients and energy derived from plants’ roots, unlike rhizobia which causes root nodules to form with their legume hosts. Non-symbiotic (also known as associative N2 fixation or associative N fixation) is not a controlled exchange of N or C between bacteria and their plant hosts.
It has been difficult to accurately determine global N inputs. It is almost impossible to get data on the productivity and area of NF legumes, and non-legumes, so BNF is hard to measure.
Gas sampling was done by using the closed chamber technique and measurements were performed after a short time of nodulation. Results of the study have revealed that cumulative fluxes were greater for the bacterial inoculated seeds than the mineral fertilization alone.
The results of the study revealed that the pepper plant significantly facilitated the biological nitrogen fixation in specifically controlled conditions. While the addition of higher amounts of biochar in the soil greatly reduced nitrogen fixation rates.
Microbial Strains for Promoting Plant Growth through Augmenting N, P, and S Nutrition
Then, they will facilitate nutrient utilization that benefits plant health. Plant microbe interaction tests can help to verify this. For decades, researchers have sought to identify optimal inoculation methods, searching for the perfect combination of different plant genotypes, and rhizobial strains, to suit particular climatic conditions and soils.
Identifying Best Microbes for Soil
Researchers have applied potassium and phosphorus strains isolated from. The wetlands along with four kinds of fertilizers viz, inorganic fertilizers, organic fertilizers, chicken manure, and microbial-based biofertilizers.
Results of this study have shown that microbial fertilizers exert significantly beneficial effects on soil enzymatic activities. On plant growth, dry weight, and the fresh weight of biomass. The microbial treatment in comparison with non-fertilizer treatments greatly increased the contents of N, P, K, and urease activities in soil.
Wang et al., 2020 experimented to check the effects of bacterial strains’ application for activation of nutrients. And promoting the growth of wheat under reduced application of fertilizers. They isolated thirty-nine plant growth-promoting rhizobacteria and investigated their potential for growth promotion. And fifteen isolates showed efficient potassium solubilization abilities. Application of these bacterial strains greatly reduced fertilizer application. By 25% and greatly improved the NPK contents, dry weight, and plant height of wheat.