Although we have only discussed only two specific
stresses, drought and freezing, many stresses induce
common physiological responses in microbes (Duguay
and Silhavy 2004). Thus, these other stresses (e.g.,
toxins, heat, anaerobiosis, and others) should alter
June 2007 NEW DIRECTIONS IN MICROBIAL ECOLOGY 1391
SPECIAL
FEATURE
microbial resource allocation in ways similar to those
identified in Fig. 2: a shift from growth to acclimation
and survival-related metabolism, with similar consequences
for ecosystem-level C and N flows. Additionally,
there is interaction among stressors; actively
growing organisms are more vulnerable to stress, so
one stress that reduces growth rates can thereby induce
tolerance to other stresses (Colucci and Inniss 1996,
Robinson 2001). The influences of all types of stress
operate at both physiological and community composition
levels and these interact to produce the overall
linkage between environmental conditions and biogeochemical
processes (Fig. 1). While the physiological
effects likely regulate short-term responses of soil
communities and processes, shifts in community composition
are likely to regulate them over longer periods.
The importance of stress in structuring the composition
and function of soil microbial communities suggests that
our current conception of microbial ‘‘functional groups’’
based largely on process-based groups such as nitrifiers
or denitrifiers, requires an additional dimension of
environmental response, such as drought tolerators, or
cold acclimators, to fully account for microbial process
responses to environmental change. This matrix of
function and environmental response creates the niche
space that presumably drives the patterns of microbial
diversity found in soil.
Developing the full flow of the linkage between
environment and processes via physiology and community
composition has been a major theme in plant
ecology over the last decade or more (Chapin et al.
2002). Achieving the goal of effectively integrating
microbial ecology into ecosystem ecology will require a
similar focus within microbial research, integrating
microbial physiological ecology, population biology,
and process ecology, and evaluating how they are
manifested at the ecosystem scale. While developing a
synthesis continues to be a major challenge, we believe
that it is not only achievable, but critical in advancing
our understanding of ecosystem ecology.