What are the nutrients in the rhizosphere and role of plant growth-promoting rhizobacteria in drought tolerance?
Respected Sir,
Rk Naresh
The rhizosphere is the soil region influenced by the roots of plants, and it is a dynamic zone where various interactions between plant roots, soil, and microorganisms take place. The availability of nutrients in the rhizosphere is crucial for plant growth, and plant growth-promoting rhizobacteria (PGPR) play a significant role in enhancing nutrient availability and promoting drought tolerance. Here are some key nutrients in the rhizosphere and the role of PGPR in drought tolerance:
Nutrients in the Rhizosphere:
· Nitrogen (N): Nitrogen is an essential nutrient for plant growth, and it is often present in the soil in various forms, including organic and inorganic nitrogen compounds.
· Phosphorus (P): Phosphorus is a vital nutrient for energy transfer in plants, and it is often present in the soil as phosphate compounds.
· Potassium (K), Calcium (Ca), Magnesium (Mg): These are macronutrients required for various physiological processes in plants.
· Micronutrients: Trace elements such as iron (Fe), zinc (Zn), copper (Cu), manganese (Mn), molybdenum (Mo), and boron (B) are essential in smaller quantities for plant growth.
Role of PGPR in Drought Tolerance:
· Improving Nutrient Availability: PGPR enhance the availability of nutrients to plants by solubilizing minerals, fixing atmospheric nitrogen, and promoting the release of bound nutrients in the soil. This is particularly important during drought conditions when water scarcity can limit nutrient uptake by plants.
· Production of Plant Growth-Promoting Substances: Many PGPR produce plant growth-promoting substances, such as indole-3-acetic acid (IAA), which is a type of auxin. Auxins stimulate root development, helping plants explore a larger soil volume for water and nutrients.
· Enhancing Water Use Efficiency: Some PGPR help plants use water more efficiently by improving the water-holding capacity of the soil and promoting the development of a robust root system. This is crucial for plants to withstand and recover from drought stress.
· Inducing Stress Tolerance: PGPR can induce systemic resistance in plants, making them more resilient to drought stress. This is achieved through the activation of stress-responsive genes and the production of compounds that protect plants from the harmful effects of drought.
· Biofilm Formation: Some PGPR form biofilms around plant roots, acting as a protective barrier that helps prevent water loss and enhances the plant's ability to cope with drought conditions.
In summary, PGPR contribute to drought tolerance in plants by improving nutrient availability, promoting efficient water use, inducing stress tolerance, and forming beneficial associations with plant roots. These interactions are essential for sustainable agriculture, especially in regions prone to water scarcity.
These microbes play a vital role in plant growth through the production of bacterial phytohormones, exopolysaccharides (EPSs), and associated metabolites by increasing the nutrient availability in the rhizosphere and protecting the plants from abiotic stresses. Plant growth promoting rhizobacteria (PGPR) is a group of bacteria that can be found in the rhizosphere. “Plant growth promoting bacteria” refers to bacteria that colonize the roots of plants (rhizosphere) that enhance plant growth. Plant growth-promoting rhizobacteria (PGPR) eliminate the effect of drought stress by altering root morphology, regulating the stress-responsive genes, producing phytohormones, osmolytes, siderophores, volatile organic compounds, and exopolysaccharides, and improving the 1-aminocyclopropane-1-carboxylate deaminase. The plant growth-promoting rhizobacteria (PGPR) are the beneficial microorganism that colonizes rhizosphere and help in promoting plant growth, protecting from biotic and abiotic stresses, and significantly increasing soil fertility. Some rhizobacteria are able to produce phytohormones, including cytokinins, auxins, gibberellins, ethylene, and abscisic acid (ABA), which play a role in different growth processes in plants, including cell multiplication, which results in increased cell and root expansion. Plant growth-promoting rhizobacteria include a diverse group of free-living soil bacteria that can improve host plant growth and development in heavy metal contaminated soils by mitigating toxic effects of heavy metals on the plants. The rhizosphere serves as the microbial seed bank where microorganisms transform organic and inorganic substances in the rhizosphere into accessible plant nutrients as plants harbor diverse microorganisms such as fungi, bacteria, nematodes, viruses, and protists among others.
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