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Soil microbiology is the study of microorganisms in soil, their functions, and how they affect soil properties. [1] It is believed that between two and four billion years ago, the first ancient bacteria and microorganisms came about on Earth's oceans.
One bacterium is capable of producing 16 million more in just 24 hours. Most soil bacteria live close to plant roots and are often referred to as rhizobacteria. Bacteria live in soil water, including the film of moisture surrounding soil particles, and some are able to swim by means of flagella.
They live on and in plants and animals. Most do not cause diseases, are beneficial to their environments, and are essential for life. [4] [34] The soil is a rich source of bacteria and a few grams contain around a thousand million of them. They are all essential to soil ecology, breaking down toxic waste and recycling nutrients.
The use of agricultural chemicals has been linked to the decline of plant and animal species, as well as harm to soil biodiversity, including bacterial and fungal communities. [ 12 ] [ 13 ] Chemical plant protection products can alter agricultural soils by affecting their physical properties such as texture, permeability, and porosity.
Nitrogen fixed by crusts has been shown to leak into surrounding substrate and can be taken up by plants, bacteria, and fungi. Nitrogen fixation has been recorded at rates of 0.7–100 kg/ha per year, from hot deserts in Australia to cold deserts. [11] Estimates of total biological nitrogen fixation are ~ 49 Tg/year (27–99 Tg/year). [10]
Consequences include corrosion damage, reduced plant growth, erosion due to loss of plant cover and soil structure, and water quality problems due to sedimentation. Salination occurs due to a combination of natural and human-caused processes. Arid conditions favour salt accumulation. This is especially apparent when soil parent material is saline.
Factors leading to wounds in plants include cultural practices, grafting, freezing injury, growth cracks, soil insects, and other animals in the environment causing damage to the plant. Consequently, in exceptionally harsh winters, it is common to have an increased incidence of crown gall due to the weather-related damage. [ 42 ]
Bacteria and archaea are almost always microscopic, while a number of eukaryotes are also microscopic, including most protists, some fungi, as well as some micro-animals and plants. Viruses are generally regarded as not living and therefore not considered to be microorganisms, although a subfield of microbiology is virology , the study of viruses.