Agriculture Reference
In-Depth Information
from native and agricultural soils at KBS LTER (Eichorst et al. 2011). The distribu-
tion of Acidobacteria varied with the C content of soil. In particular, subdivision 4
of Acidobacteria was most abundant in agricultural soils (Fig. 6.3B), which contain
less organic C than forested soils (Paul et al. 2015, Chapter 5 in this volume).
Given that plants are the major source of organic C for soil microbes, it is
reasonable to expect a coupling between the composition of plant and microbial
communities in terrestrial ecosystems. Both physiological phospholipid fatty acid
(PLFA) profiles and metabolic Biolog assays of rhizosphere soils obtained from
different plant species indicate that plant species composition impacts microbial
activity and functional diversity within soil microbial communities (Broughton and
Gross 2000). Further, tRFLP fingerprints of DNA extracted from various soil frac-
tions indicate that the highest diversity of microorganisms is associated with rap-
idly cycling soil C from freshly deposited plant residues (Paul et al. 2015, Chapter
5 in this volume). These studies also reveal that heterogeneity in soil microbial
communities results from small-scale spatial heterogeneity in the availability and
composition of plant residues, which is consistent with plant biomass as a driver
of microbial community structure. Molecular surveys of microbial communities in
soil provide a means to identify environmental factors that influence community
structure and help set the stage for studies that relate the structure of microbial com-
munities with their functions.
Relating Structure and Function of Microbial Communities
Relationships between Biological Diversity and Function
Ongoing studies at the Cedar Creek LTER (e.g., Tilman et al. 2001) and else-
where (e.g., Suding et al. 2005) are exploring relationships between plant species
diversity and ecosystem function. These studies have demonstrated, for instance,
that plant diversity is positively correlated with net primary productivity (Tilman
et al. 2001) and C sequestration in soil (Adair et al. 2009). Although the underly-
ing explanation for such diversity-function relationships is vigorously debated,
complementary contributions from different plant species appear to be of funda-
mental importance (Fargione et al. 2007). Given the positive relationship between
the diversity of plant species and the magnitude of ecosystem processes, we asked
if there might be similar relationships between bacterial communities and the pro-
cesses they catalyze in KBS LTER ecosystems. Evidence from elsewhere sug-
gests that such a relationship is unlikely for those microbially catalyzed processes,
such as biomass decomposition, involving a wide variety of organisms (Schimel
1995, Groffman and Bohlen 1999). However, the number of species in a bacte-
rial community (species richness) may be important for those processes catalyzed
by fewer, more specialized species (Cavigelli and Robertson 2000). Given that
microbes are responsible for the exchange of greenhouse gases with the atmo-
sphere, including the consumption of atmospheric CH
4
and production of N
2
O,
the relationships among bacterial diversity and these processes seem especially
important to explore.
