IV. DESERT ALGAE, LICHENS, AND FUNGI
171
Stichococcus, Gongrosira, Cylindrocystis, and Cosmarium; Xanthophyceae—Pleurochloris, Chloridella, Botrydiopsis, Polyedrella, Gloeobotrys, Bumilleriopsis,
Heterothrix,
Tribonema,
and
Heterococcus;
diatoms—Stauroneis, Navicula, Pinnularia, and Hantzschia.
But (1967) describes several soil algal associations from the high
deserts of Western Pamir. The dominant species are blue-green algae
(Plectonema, Phormidium, Amor phono stoc, and Microcoleus), Xanthophyceae (Pleurochloris and Heterothrix), and diatoms (Navicula). Besides
these, species of Botrydiopsis, Hantzschia, Tolypothrix, and Chlorella may
be subdominant.
Peculiar conditions seem to prevail in the extremely dry Atacama
Desert. Forest and Weston (1966) report Anacystis montana (Lightf.)
Drouet et Daily, Coccochloris peniocystis (Kütz.) Drouet et Daily, and
Schizothrix calcicola (Ag.) Gom. (uncertain). Schwabe (1963) obtained
from laboratory cultures of Atacama soils four unusual blue-green algae:
Calothrix desertica Schwabe, Plectonema polymorphum Schwabe var.
viridis Schwabe, Schizothrix adunca Schwabe, and Schizothrix atacamensis
Schwabe. These organisms are said to represent the total algal flora. They
are slow both in germination and in growth and are resistant to high levels
of irradiation and to desiccation. In sterile sand cultures, the algae penetrate the surface and grow into small cushion-like pellets (Fig. 2a) formed
by the gelatinous sheaths of the filaments which glue the sand grains into
a compact mass. In nature, the algal pellets presumably shade the underlying soil portion from evaporation and thus each pellet creates in effect
a tiny water reservoir. A peculiar association exists between Calothrix
desertica Schwabe and Schizothrix atacamensis Schwabe. These two species form joint colonies in which the upper part is formed by a cushion-like
mat of Calothrix with an underlying layer of Schizothrix (Fig. 2b). These
structures may represent one of the peculiar ecological adaptations in algae
to extreme xeric desert conditions.
Cameron (1964b, 1969) found that in desert soil algae, spore-producing
forms are notably rare. However, Bolyshev (1968) reports that sporeforming algae such as Anabaena variablis Kütz. f. rotundispora Hollerb.,
Nodularia harveyana (Thwaites) Thuret, and Anabaena salicola Kondratieva are characteristic of salt-desert solonchak soils in Central Asia, and
he considers spore formation as an adaptive phenomenon which enables
these forms to survive prolonged periods of high salt concentration.
b. Epedaphic A Igae. These algae live on the surface of the soil and usually form visible growths there. They are widely distributed in deserts and
semideserts and may form, as in the Central Asian takyr, a very conspicuous crust. In extremely dry deserts, however, they seem to be absent or
infrequent. The literature on epedaphic algae is extensive (Bolyshev, 1952,
171
Stichococcus, Gongrosira, Cylindrocystis, and Cosmarium; Xanthophyceae—Pleurochloris, Chloridella, Botrydiopsis, Polyedrella, Gloeobotrys, Bumilleriopsis,
Heterothrix,
Tribonema,
and
Heterococcus;
diatoms—Stauroneis, Navicula, Pinnularia, and Hantzschia.
But (1967) describes several soil algal associations from the high
deserts of Western Pamir. The dominant species are blue-green algae
(Plectonema, Phormidium, Amor phono stoc, and Microcoleus), Xanthophyceae (Pleurochloris and Heterothrix), and diatoms (Navicula). Besides
these, species of Botrydiopsis, Hantzschia, Tolypothrix, and Chlorella may
be subdominant.
Peculiar conditions seem to prevail in the extremely dry Atacama
Desert. Forest and Weston (1966) report Anacystis montana (Lightf.)
Drouet et Daily, Coccochloris peniocystis (Kütz.) Drouet et Daily, and
Schizothrix calcicola (Ag.) Gom. (uncertain). Schwabe (1963) obtained
from laboratory cultures of Atacama soils four unusual blue-green algae:
Calothrix desertica Schwabe, Plectonema polymorphum Schwabe var.
viridis Schwabe, Schizothrix adunca Schwabe, and Schizothrix atacamensis
Schwabe. These organisms are said to represent the total algal flora. They
are slow both in germination and in growth and are resistant to high levels
of irradiation and to desiccation. In sterile sand cultures, the algae penetrate the surface and grow into small cushion-like pellets (Fig. 2a) formed
by the gelatinous sheaths of the filaments which glue the sand grains into
a compact mass. In nature, the algal pellets presumably shade the underlying soil portion from evaporation and thus each pellet creates in effect
a tiny water reservoir. A peculiar association exists between Calothrix
desertica Schwabe and Schizothrix atacamensis Schwabe. These two species form joint colonies in which the upper part is formed by a cushion-like
mat of Calothrix with an underlying layer of Schizothrix (Fig. 2b). These
structures may represent one of the peculiar ecological adaptations in algae
to extreme xeric desert conditions.
Cameron (1964b, 1969) found that in desert soil algae, spore-producing
forms are notably rare. However, Bolyshev (1968) reports that sporeforming algae such as Anabaena variablis Kütz. f. rotundispora Hollerb.,
Nodularia harveyana (Thwaites) Thuret, and Anabaena salicola Kondratieva are characteristic of salt-desert solonchak soils in Central Asia, and
he considers spore formation as an adaptive phenomenon which enables
these forms to survive prolonged periods of high salt concentration.
b. Epedaphic A Igae. These algae live on the surface of the soil and usually form visible growths there. They are widely distributed in deserts and
semideserts and may form, as in the Central Asian takyr, a very conspicuous crust. In extremely dry deserts, however, they seem to be absent or
infrequent. The literature on epedaphic algae is extensive (Bolyshev, 1952,