Title |
Growth of cyanobacterial soil crusts during diurnal freeze-thaw cycles |
Author |
Steven K. Schmidt* and Lara Vimercati |
Address |
Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, 80309, USA |
Bibliography |
Journal of Microbiology, 57(4),243–251, 2019,
|
DOI |
10.1007/s12275-019-8359-5
|
Key Words |
biological soil crusts, Nostoc commune, terraforming
Mars, extremophiles, glacier retreat, soil stabilization,
BSCs, astrobiology |
Abstract |
Various Nostoc spp. and related cyanobacteria are able to survive
extreme temperatures and are among the most successful
colonists of high-elevation sites being exposed due to glacial
retreat. It is unclear, however, if cyanobacteria can grow
during the extreme freeze-thaw cycles that occur on a yearround
basis at high-elevation, peri-glacial sites or if they only
grow during the rare periods when freeze-thaw cycles do not
occur. We conducted several experiments to determine if cyanobacteria
that form biological soil crusts (BSCs) at highelevation
sites (> 5,000 m.a.s.l.) in the Andes can grow during
diurnal freeze-thaw cycles on a par with those that occur in
the field. Here we show that a soil crust that had been frozen
at -20°C for five years was able to increase from 40% to 100%
soil coverage during a 45-day incubation during which the
soil temperature cycled between -12°C and 26°C every day.
In a second, experiment an undeveloped soil with no visible
BSCs showed a statistically significant shift in the bacterial
community from one containing few cyanobacterial sequences
(8% of sequences) to one dominated (27%) by Nostoc,
Microcoleus, and Leptolyngbya phylotypes during a 77-day
incubation with daily freeze-thaw cycles. In addition, counts
of spherical Nostoc-like colonies increased significantly on
the soil surface during the experiment, especially in microcosms
receiving phosphorus. Taken together these results
show that freeze-thaw cycles alone do not limit the growth
of BSCs in high-elevation soils, and provide new insight into
how life is able to thrive in one of the most extreme terrestrial
environments on Earth. |