Linking microbial communities and
ecosystem functioning
Teri C. Balser, tcbalser@facstaff.wisc.edu

Traditionally, ecosystem scientists have
focused on the role of abiotic factors such as
temperature or water in controlling process
rates while microbiologists have focused on
the population ecology of microorganisms.
More and more, however, we are seeing
microbial ecology studies showing that
microorganisms can be explicit determinants
of soil function and nutrient availability. The
impact of future global changes may best be
addressed by research that integrates
population and community ecology with
process study.

My work was designed to further this
integration. I addressed two questions: 1)
How should we measure microbial
community composition and function, in order
to link microbiology and nutrient cycling at the
ecosystem scale? 2) What is the relative
importance of microbial community
characteristics versus abiotic factors (such as
temperature or soil water) in controlling
nutrient cycles and ecosystem response to
climate change or disturbance?

To make a quantitative link between
measures of community characteristics
(biomass, activity, diversity) and ecosystem
processes, I combined a field manipulation of
climate (reciprocal soil transplant between
grassland and conifer ecosystems in the
Sierra Nevada of California) with a suite of
laboratory analyses to tease apart the
relationships among changes in
environment, microbial community
characteristics, and soil processes. I worked
extensively with two techniques for studying
soil communities: phospholipid fatty acid
analysis (PLFA), and substrate utilization
patterns (BiOLOG assay). From this I gained
an understanding of the temporal patterns of
community change after disturbance and how
this constrains process rates.

In addition to developing a quantitative
framework for linking microbial community
characteristics with nutrient cycles, I was
interested in whether microbial communities
from different ecosystems respond the same
way to a given change in environment. I found
that the grassland and conifer microbial
communities I studied did not respond the
same way to a change in climate. Further
study indicated that these and other microbial
communities (from Puerto Rico and Alaska)
are adapted to their native climatic regime.
This suggests that a soil community in an
area of wide climatic fluctuation may respond
to global changes and disturbance very
differently than a community from a stable
environment.