The ecosystem-level cost of inducing freeze-tolerance
appears to be substantial. In Arctic tundra, as soil
temperatures drop to near 08C and microbes must
induce cold-acclimation mechanisms, they increase their
metabolism of material from the ‘‘microbial biomass
and products (MB and P)’’ pool—the small, rapidly
turning over, N-rich pool that is comprised of material
from live and dead cells (Fig. 3; Schimel and Mikan
2005). This metabolic shift is large enough to change
overall patterns of ecosystem C and N cycling from net
N immobilization during the growing season to net
mineralization during the winter, when all the measurFIG.
3. Respiration from microbial biomass and products (MB and P) and from detritus in inter-tussock soil as temperatures
drop from þ58C to 98C. The figure is reproduced from Schimel and Mikan (2005).
1390 JOSHUA SCHIMEL ET AL. Ecology, Vol. 88, No. 6
SPECIAL
FEATURE
able annual net mineralization occurs in Alaskan
tussock tundra (Giblin et al. 1991, Schimel et al. 2004).
An important component of this physiological shift is
that it occurs above 08C; thus, rather than waiting for
the freezing stress to occur, microbes appear to preacclimate
to the stress, analogous to frost hardening in
plants (Lennartsson and Ogren 2002)