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A diazotroph is a microorganism that is able to grow without external sources of fixed nitrogen. Examples of organisms that do this are rhizobia and Frankia and Azospirillum. All diazotrophs contain iron-molybdenum or iron-vanadium nitrogenase systems. Two of the most studied systems are those of Klebsiella pneumoniae and Azotobacter vinelandii ...
They sequester nitrogen and other nutrients that might otherwise enter groundwater, and they fix nitrogen from the atmosphere, making it available to plants. Many organisms enhance soil aggregation and porosity, thus increasing infiltration and reducing surface runoff. Soil organisms prey on crop pests and are food for above-ground animals.
Biological soil crusts are most often [3] composed of fungi, lichens, cyanobacteria, bryophytes, and algae in varying proportions. These organisms live in intimate association in the uppermost few millimeters of the soil surface, and are the biological basis for the formation of soil crusts.
Soil salinity can vary between extremes in a relatively small area; [27] this allows plants to seek areas with less salinity. It is hard to determine which plants can grow in soil with high salinity because the soil salinity is not uniform, even in small areas. [27] However, plants absorb nutrients from areas with lower salinity. [27]
The soil is home to a large proportion of the world's biodiversity.The links between soil organisms and soil functions are complex. The interconnectedness and complexity of this soil 'food web' means any appraisal of soil function must necessarily take into account interactions with the living communities that exist within the soil.
Fungi are abundant in soil, but bacteria are more abundant. Fungi are important in the soil as food sources for other, larger organisms, pathogens, beneficial symbiotic relationships with plants or other organisms and soil health. Fungi can be split into species based primarily on the size, shape and color of their reproductive spores, which ...
Soil regeneration is the reformation of degraded soil through biological, chemical, and or physical processes. [ 2 ] When productivity declined in the low-clay soils of northern Thailand, farmers initially responded by adding organic matter from termite mounds , but this was unsustainable in the long-term.
Soil is the most speciose (species-rich) ecosystem on Earth, but the vast majority of organisms in soil are microbes, a great many of which have not been described. [ 71 ] [ 72 ] There may be a population limit of around one billion cells per gram of soil, but estimates of the number of species vary widely from 50,000 per gram to over a million ...