Agriculture Reference
In-Depth Information
Based on this body of research, one might expect that bacteria that make effi-
cient use of resources are favored in habitats where the concentration of resources
is perpetually low. A minimum concentration of resources is required to provide
maintenance energy, which is the sum of energy expenditures that are not directed
toward growth, for example, maintaining a charged membrane or motility. At very
low resource concentrations, the majority of assimilated C is therefore respired
for maintenance purposes. Under these conditions, most C resources will be oxi-
dized to CO
2
to provide energy rather than biomass. Consequently, bacterial growth
efficiency should be low in resource-limited environments. When C and nutrient
resources are more abundant, a greater proportion of assimilated C can be allocated
to biomass production, making growth efficiency higher. Studies to measure the
efficiency of C utilization in different MCSE systems are under way and will be
a reasonable test of this model's ability to accurately predict the composition of
bacterial communities in soil.
Summary
Microbial communities in soil are critical to the productivity and health of the bio-
sphere and, in particular, to the cycling of C and N that underpin agricultural pro-
ductivity and climate change. However, we are only just beginning to understand
the composition and function of these complex soil microbial assemblages. The
replicated array of managed and unmanaged ecosystems at KBS LTER has been
an invaluable resource for studying the effects of land use on soil microbial com-
munities and their impact on the biosphere. Molecular surveys reveal a tremendous
taxonomic and functional diversity of microbes in KBS LTER soils—a diversity so
large that even state-of-the-art, large-scale DNA sequencing methods have yet to
reveal its full extent. Despite the challenges associated with measuring this enor-
mous diversity, there are clear patterns in the distribution of microbes across the
KBS LTER landscape, and the relationships between the structure of microbial
communities and ecosystem-level processes such as C and N cycling are being
revealed. One of the most striking relationships uncovered to date is the positive
correlation between methanotroph diversity and CH
4
consumption.
As we continue gathering fundamental information about the structure of dif-
ferent bacterial communities, we must ask more questions about the connections
between their varying compositions and the major ecological functions that are
altered by agronomic management. It is particularly important that we begin to
address cause and effect: Is a function modified directly by a change in the bacterial
community, or are they independently influenced by land use?
The answers to these questions will affect future microbial research at KBS
LTER in two key ways. The first will be to accelerate evolution of the current,
largely observational approach to a more experimental strategy that manipulates
variables
in-situ
to test hypotheses about the role of the bacterial community. These
experiments will then lead to the second phase of research: developing and evalu-
ating practices to maximize agricultural productivity while reducing environmen-
tal impact. If these practical applications involve direct manipulation of bacterial
