Which group of microorganisms has the highest population in the soil and role of rhizosphere microorganisms on plant growth?
The group of microorganisms that typically has the highest population in the soil is bacteria. Bacteria are highly abundant in soil, with populations ranging from millions to billions per gram of soil. They play essential roles in nutrient cycling, organic matter decomposition, and various other soil processes.
The rhizosphere is the narrow region of soil that is directly influenced by root exudates, which are organic compounds released by plant roots. The rhizosphere is characterized by a higher microbial activity compared to the bulk soil. Rhizosphere microorganisms have a significant impact on plant growth, and their roles include:
The interactions between plants and rhizosphere microorganisms are dynamic and complex, forming a mutualistic relationship that benefits both the plants and the microorganisms. These interactions are crucial for plant health, nutrient availability, and overall soil fertility.
These are bacteria, actinomycetes, fungi, and algae. Each of these groups is made up of many genera and hundreds of species. Bacteria constitute the most abundant group of microorganisms in soil, and they are also the smallest living organisms, apart from viruses that live in the cells of other organisms. Fungi are the group of microorganisms that have the highest biomass in the soil. The maximum limit is up to 790 μg C/g soil and it is found in the soil with surface organic horizons in the form of thin moss/lichen litters, in which the development of fungal mycelium is most active. By far, the most numerous microbes in soil are bacteria, which have just one cell. Also abundant are fungi, which produce long, slender strings of cells called filaments, or hyphae. The actinomycetes are in-between these two organisms. They are advanced bacteria that can form branches like fungi. The two most abundant groups of microbes are the fungi and bacteria. Fungi are distinct from bacteria in that they are eukaryotic and generally produce filamentous hyphae that can penetrate and explore microhabitats of the soil. We know that rhizosphere microbiota protect against pathogens, improve growth by producing phytohormones, and may help plants withstand environmental perturbations such as abnormal variation in temperature, drought, and salinity related to climate. It is known that under adverse living conditions plants gain advantage if the protective rhizosphere associations contain microorganisms that perform a wide range of functions, including plant nutrition, resistance to abiotic stresses, biocontrol and the removal of pollutants from soil. Rhizobacteria reside in the rhizosphere, and those having beneficial effects on plants are termed plant growth-promoting rhizobacteria. These rhizobacteria are equipped with a number of mechanisms (both direct and indirect) through which they improve plant growth in diverse agricultural settings. The rhizosphere harbors diverse microbial groups that perform various functions and exert numerous effects on plant growth. They are involved in nutrient cycling, protecting from phytopathogens as well as under biotic and abiotic stress conditions, and some may act as plant pathogens.
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