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Soil Habitats - Lithosphere

Soil Habitats - Lithosphere -Soil constitutes the major habitat of terrestrial microorganisms. Soil is a favourable habitat for the microbes. Higher number occurs in the organically rich surface layers than in the underlying mineral soils. Particularly high numbers of microbes occur in association with plant roots. Fungal populations arc favoured in soils of low pH, and bacteria tend to occur in higher numbers in those of higher pH.

Soils have many different microhabitats. A higher proportion of Gram positive bacteria arc found in soil than in freshwater and marine habitats. Many different genera of bacteria arc commonly found in soil, actinomycetes comprising a significant proportion of the bacterial community (sec below)
Fungi constitute the major proportion of the microbial biomass in soils. Fungi occur as free living or associated with plant roots.

Most common soil fungi are Fungi Imperfecti, but numerous Ascomycetes and Basidiomycetes also occur. Most soil fungi are opportunistic, being active under favourable conditions. Many soil fungi are able to degrade polysaccharides such as cellulose, hemicellulose and a few also lignin. Organic matter in soil is lar­gely composed of humus.

Microbes in soil are responsible for biodegradation and mineral cycling. Important plant polymers as cellulose and lignin are degraded exclusively by soil microbes. Since carbon and nitrogen are the chief macroelements essential for all organisms, the soil microbes play an important role in cycling of these elements in the biosphere.

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