IV. DESERT ALGAE, LICHENS, AND FUNGI
181
the nightly dew condensation. Under arid conditions the daily temperature
fluctuation of soil or rock surface layers is much higher than macroclimatic conditions would indicate, and this is why nightly water condensation frequently occurs in deserts. Unfortunately, very few data are available
on dew fall in desert areas. But Table I, based on the work of Evenari
et al (1963-1968) at the Avdat Experimental Farm in Israel provides
some pertinent information. It shows that while rainfall was variable in
quantity, limited to a few winter days, and unevenly distributed, the
amount of dew was remarkably constant over 5 years of measurement.
It was also evenly distributed throughout the year.
In practically all desert algal habitats water is conserved by the physical
microstructure of the environment, such as the capillaries of soil, fissures
or pores of rocks, etc. In these spaces, however, the water does not necessarily stay in liquid form but is perhaps present only as a higher vapor
pressure. Lange (1969b) and Lange et al. (1968, 1970a,b) have shown
that desert lichens are capable of using atmospheric vapor as a water
source, and it is quite probable that algae can do the same.
None of the water-conserving devices will, however, prevent occasional
desiccation which occurs, for instance, during extended dry spells. Draught
resistance in some algae is considerable. Since Bristol's report (1919), it
is well known that soil algae (green and blue-green algae and diatoms)
may retain their viability in dry conditions for surprisingly long periods.
Bristol was able to culture algae from dry samples preserved in the laboratory for up to 70 years and Parker et al. (1969) after 60 years.
Trainor (1962) obtained both green and blue-green algal growth from
soil samples which were oven dried at 100°C for 1 hour, and one green
alga {Chlorella) even survived desiccation for 1 hour at 130°C. Cameron
et al. (1970b) reported that different desert soil microorganisms such as
coccoid green algae, filamentous and coccoid blue-green algae, and the
mold Altemaria sp. survived after 5 years of exposure to continuous high
vacuum. However, the recent work of Trainor (1970) demonstrated
that only a few of the "typical" soil algal species possess the capacity to
survive in desiccated condition for prolonged periods, and it is obvious
that only those forms which are able to do so can survive in desert
environments.
endolithic alga (a small-celled Gloeocapsa sp.), the coherence of the crystal components of the rock is reduced and thus the rock splits easily along the algal zone,
separating the surface crust from the rest of the substrate. The micrograph shows a
portion of the lower surface of such a separated surface crust. Between the rhombic
calcite crystals, the air spaces result in a porous rock structure. The colonies of algae
adhere to the crystal surfaces. χΙΟΟΟ. After Friedmann (1971).
181
the nightly dew condensation. Under arid conditions the daily temperature
fluctuation of soil or rock surface layers is much higher than macroclimatic conditions would indicate, and this is why nightly water condensation frequently occurs in deserts. Unfortunately, very few data are available
on dew fall in desert areas. But Table I, based on the work of Evenari
et al (1963-1968) at the Avdat Experimental Farm in Israel provides
some pertinent information. It shows that while rainfall was variable in
quantity, limited to a few winter days, and unevenly distributed, the
amount of dew was remarkably constant over 5 years of measurement.
It was also evenly distributed throughout the year.
In practically all desert algal habitats water is conserved by the physical
microstructure of the environment, such as the capillaries of soil, fissures
or pores of rocks, etc. In these spaces, however, the water does not necessarily stay in liquid form but is perhaps present only as a higher vapor
pressure. Lange (1969b) and Lange et al. (1968, 1970a,b) have shown
that desert lichens are capable of using atmospheric vapor as a water
source, and it is quite probable that algae can do the same.
None of the water-conserving devices will, however, prevent occasional
desiccation which occurs, for instance, during extended dry spells. Draught
resistance in some algae is considerable. Since Bristol's report (1919), it
is well known that soil algae (green and blue-green algae and diatoms)
may retain their viability in dry conditions for surprisingly long periods.
Bristol was able to culture algae from dry samples preserved in the laboratory for up to 70 years and Parker et al. (1969) after 60 years.
Trainor (1962) obtained both green and blue-green algal growth from
soil samples which were oven dried at 100°C for 1 hour, and one green
alga {Chlorella) even survived desiccation for 1 hour at 130°C. Cameron
et al. (1970b) reported that different desert soil microorganisms such as
coccoid green algae, filamentous and coccoid blue-green algae, and the
mold Altemaria sp. survived after 5 years of exposure to continuous high
vacuum. However, the recent work of Trainor (1970) demonstrated
that only a few of the "typical" soil algal species possess the capacity to
survive in desiccated condition for prolonged periods, and it is obvious
that only those forms which are able to do so can survive in desert
environments.
endolithic alga (a small-celled Gloeocapsa sp.), the coherence of the crystal components of the rock is reduced and thus the rock splits easily along the algal zone,
separating the surface crust from the rest of the substrate. The micrograph shows a
portion of the lower surface of such a separated surface crust. Between the rhombic
calcite crystals, the air spaces result in a porous rock structure. The colonies of algae
adhere to the crystal surfaces. χΙΟΟΟ. After Friedmann (1971).