76
WALLACE H. FULLER
1965) indicate that soil fungi most often are the least abundant population group in desert soils. However, as pointed out so well by Alexander
(1961), methods of enumeration favor the small size of the bacterial cell,
which ranges from less than 0.2 /xm to a maximum of about 5 μ,ιη, when in
effect in most well-aerated soils, the mass of total fungal protoplasm exceeds that of other microorganisms. Soil algae also suffer for the same reason in enumeration studies.
On the basis of enumeration data, nevertheless, the fungi in the harsh
deserts examined in North and South America are reported to be least
abundant of the microorganisms (Cameron, 1966). In the barren Atacama
Desert, only three species of fungi were found (Cameron et al, 1965).
Pénicillium is most common to desert soils. There appears to be no simple
correlation between specific fungi and soil type or series or climate. In Central Iraq, a large number of fungal species were isolated with a decreasing
order of dominance of Hormodendrum, Aspergillus, Fusarium, Alternaria,
and Pénicillium, but no correlations were evident (Al-Doory et ai, 1959).
Large populations of diverse species are reported for North African deserts
(Nicot, 1955), Sudan (Nour, 1956), Nevada (Durrell and Shields, 1960),
Egypt (Sabet, 1939), and Mauritania (Audry and Rossetti, 1962). Over
102 species of fungi are reported from the Judean Desert and the Northern
Negev (Rayss and Borut, 1958). A great number of Aspergillus spp. and
Pénicillium spp. occur in desert soils.
G. SPECIALIZED ORGANISMS
Specialized microorganisms often are the most conspicuous forms found
in deserts. For example, diatoms (Bacillariophyta) appear in salt crusts
and where rainwater accumulates and evaporates leaving salt deposits. Old
lake beds, relics of more humid climates, may be teeming with diatoms.
Algal crusts may dominate the surface of takyr soils. Sulfur-oxidizing bacteria are abundantly present where sulfides, sulfur and sulfur minerals are
present. Hot springs and sulfurous desert waters favor the presence of sulfur oxidizers. In the cold Valley of 10,000 Smokes Desert in Alaska, sulfur
as well as iron-oxidizing microorganisms concentrate where sulfur fumes
escape from the land and moisture is available (Cameron, 1966). Algae
and lichen form prominent crusts on bare desert soil surfaces and lichens
color bare rock surfaces. In desert soil ecosystems, slight changes in the
presence of certain chemical compounds, moisture, temperature and organic matter determine the presence or absence, abundance or poverty of
specialized organisms. Microenvironment is important in soil biology,
particularly in arid climates. For further discussion of desert cryptogams
(see Chapter V, Volume I and Chapter IV, this volume).
WALLACE H. FULLER
1965) indicate that soil fungi most often are the least abundant population group in desert soils. However, as pointed out so well by Alexander
(1961), methods of enumeration favor the small size of the bacterial cell,
which ranges from less than 0.2 /xm to a maximum of about 5 μ,ιη, when in
effect in most well-aerated soils, the mass of total fungal protoplasm exceeds that of other microorganisms. Soil algae also suffer for the same reason in enumeration studies.
On the basis of enumeration data, nevertheless, the fungi in the harsh
deserts examined in North and South America are reported to be least
abundant of the microorganisms (Cameron, 1966). In the barren Atacama
Desert, only three species of fungi were found (Cameron et al, 1965).
Pénicillium is most common to desert soils. There appears to be no simple
correlation between specific fungi and soil type or series or climate. In Central Iraq, a large number of fungal species were isolated with a decreasing
order of dominance of Hormodendrum, Aspergillus, Fusarium, Alternaria,
and Pénicillium, but no correlations were evident (Al-Doory et ai, 1959).
Large populations of diverse species are reported for North African deserts
(Nicot, 1955), Sudan (Nour, 1956), Nevada (Durrell and Shields, 1960),
Egypt (Sabet, 1939), and Mauritania (Audry and Rossetti, 1962). Over
102 species of fungi are reported from the Judean Desert and the Northern
Negev (Rayss and Borut, 1958). A great number of Aspergillus spp. and
Pénicillium spp. occur in desert soils.
G. SPECIALIZED ORGANISMS
Specialized microorganisms often are the most conspicuous forms found
in deserts. For example, diatoms (Bacillariophyta) appear in salt crusts
and where rainwater accumulates and evaporates leaving salt deposits. Old
lake beds, relics of more humid climates, may be teeming with diatoms.
Algal crusts may dominate the surface of takyr soils. Sulfur-oxidizing bacteria are abundantly present where sulfides, sulfur and sulfur minerals are
present. Hot springs and sulfurous desert waters favor the presence of sulfur oxidizers. In the cold Valley of 10,000 Smokes Desert in Alaska, sulfur
as well as iron-oxidizing microorganisms concentrate where sulfur fumes
escape from the land and moisture is available (Cameron, 1966). Algae
and lichen form prominent crusts on bare desert soil surfaces and lichens
color bare rock surfaces. In desert soil ecosystems, slight changes in the
presence of certain chemical compounds, moisture, temperature and organic matter determine the presence or absence, abundance or poverty of
specialized organisms. Microenvironment is important in soil biology,
particularly in arid climates. For further discussion of desert cryptogams
(see Chapter V, Volume I and Chapter IV, this volume).