Pichia. The molds predominate in acidic soils (forest soils, podzolic soils), where
they produce a biomass of 500–1000 Kg/ha. The main genera are Mucor, Rhizopus,
Aspergillus, and Penicillium, which form 50% of the fungal biomass accompanied
by Fusarium, Alternaria, Trichoderma, Trichothecium, and Cladosporium. The
autotrophic algae, encountered in superficial layers of soil, synthesize OM. The
protozoa, mainly represented by flagellates and rhizopodes, are conditioned by their
soil moisture and the presence of OSs. They interfere in limiting the multiplication of
the MOs they use as food. Number and density of soil microorganisms. In soil the
MOs are in concentrations of 9 Á 10
7
–3 Á 10
11 cells/g dry soil. Their number is
dependent on the type of soil (about 10
8 cells/gram in clay soils, a poorer microbe in
acidic, alkaline, and sandy soils). These MOs form a total biomass of approx. 0.5–6
t/ha. Of the total of these MOs, approx. 30% are Gram-negative bacteria. The
bacteria number oscillates between 3.6 Á 10
7 and 10
11 cells/g soil, totaling a biomass
of up to 0.7 t/ha. Dominant are filamentous bacteria. Yeasts reach 10
3 cells/g soil,
growing on the plant debris. Fungi form a biomass 1–1.5 t/ha. The huge number is
due to the fact that there is always a sufficient amount of organic and mineral
substances in the soil, satisfactory humidity, sufficient oxygen, and a suitable
pH. The largest number of MOs is found in the upper layers of the soil. With the
exception of superficial layers, MOs in the soil are protected from the harmful effects
of ultraviolet rays (Somova et al. 2005).
4.2.5 The Distribution of Microorganisms in the Soil
The bacteria in the soil is in the form of associations of 5–25 cells, aggregated by the
soil particles. Spreading in the soil is dependent on the degree of oxygen access.
There are several aerobic bacteria on the surface of the soil, then some anaerobic
bacteria, and anaerobic bacteria in depth. Yeasts and microfungi are only found in
the superficial layers of the soil, being aerobic MOs. The vertical distribution of the
microbiota in the soil is unequal. The richest is the area up to 30 cm depth. The cell
concentration differs according to the nutrients the soil contains.
A higher concentration is found in the area of the rhizosphere (the plant root area).
The horizontal distribution of the native microbiota is dependent on the type of soil
that determines the selection of different physiological types adapted to the metabolism of certain types of substances present in the soil composition (Dutta and Podile
2010).
4.2.6 Factors that Determine the Distribution of Microorganisms
in the Soil
The type of MOs in the soil, as well as their number, varies depending on the
physicochemical structure of the soil but especially on the organic and inorganic
substances in the soil, the soil pH, and the amount of oxygen. The type of soil is thus
the main factor for their selection.
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M. Butu et al.
they produce a biomass of 500–1000 Kg/ha. The main genera are Mucor, Rhizopus,
Aspergillus, and Penicillium, which form 50% of the fungal biomass accompanied
by Fusarium, Alternaria, Trichoderma, Trichothecium, and Cladosporium. The
autotrophic algae, encountered in superficial layers of soil, synthesize OM. The
protozoa, mainly represented by flagellates and rhizopodes, are conditioned by their
soil moisture and the presence of OSs. They interfere in limiting the multiplication of
the MOs they use as food. Number and density of soil microorganisms. In soil the
MOs are in concentrations of 9 Á 10
7
–3 Á 10
11 cells/g dry soil. Their number is
dependent on the type of soil (about 10
8 cells/gram in clay soils, a poorer microbe in
acidic, alkaline, and sandy soils). These MOs form a total biomass of approx. 0.5–6
t/ha. Of the total of these MOs, approx. 30% are Gram-negative bacteria. The
bacteria number oscillates between 3.6 Á 10
7 and 10
11 cells/g soil, totaling a biomass
of up to 0.7 t/ha. Dominant are filamentous bacteria. Yeasts reach 10
3 cells/g soil,
growing on the plant debris. Fungi form a biomass 1–1.5 t/ha. The huge number is
due to the fact that there is always a sufficient amount of organic and mineral
substances in the soil, satisfactory humidity, sufficient oxygen, and a suitable
pH. The largest number of MOs is found in the upper layers of the soil. With the
exception of superficial layers, MOs in the soil are protected from the harmful effects
of ultraviolet rays (Somova et al. 2005).
4.2.5 The Distribution of Microorganisms in the Soil
The bacteria in the soil is in the form of associations of 5–25 cells, aggregated by the
soil particles. Spreading in the soil is dependent on the degree of oxygen access.
There are several aerobic bacteria on the surface of the soil, then some anaerobic
bacteria, and anaerobic bacteria in depth. Yeasts and microfungi are only found in
the superficial layers of the soil, being aerobic MOs. The vertical distribution of the
microbiota in the soil is unequal. The richest is the area up to 30 cm depth. The cell
concentration differs according to the nutrients the soil contains.
A higher concentration is found in the area of the rhizosphere (the plant root area).
The horizontal distribution of the native microbiota is dependent on the type of soil
that determines the selection of different physiological types adapted to the metabolism of certain types of substances present in the soil composition (Dutta and Podile
2010).
4.2.6 Factors that Determine the Distribution of Microorganisms
in the Soil
The type of MOs in the soil, as well as their number, varies depending on the
physicochemical structure of the soil but especially on the organic and inorganic
substances in the soil, the soil pH, and the amount of oxygen. The type of soil is thus
the main factor for their selection.
86
M. Butu et al.