Agriculture Reference
In-Depth Information
6
Microbial Diversity in Soils
of Agricultural Landscapes
and Its Relation to Ecosystem
Function
Thomas M. Schmidt and Clive Waldron
The taxonomic and functional diversity of microbes in soil is stunning. Although
they are largely invisible to the naked eye, microbes are pervasive in nature and
have a profound impact on Earth's habitability. Like many other terrestrial environ-
ments, the top layer of soil at the Kellogg Biological Station Long-Term Ecological
Research site (KBS LTER) typically contains 1 × 10
9
microbes per gram of dry soil,
representing between 10,000 and a million species (Gans et al. 2005). Extrapolating
the estimated number of microbes in individual soil samples to a global scale yields
an estimate of an incredible 26 × 10
28
microbes in terrestrial habitats (Whitman
et al. 1998). Combined with estimates of microbial abundance in aquatic and sub-
surface environments, Whitman and colleagues (1998) estimated that microbes
contain at least half of the amount of carbon (C) stored in plants and 10 times more
nitrogen (N) and phosphorus (P).
The cycling of C, N, P, and other less abundant elements that pass through soil
microbial communities influences environments as small as soil aggregates and as
far-reaching as global climate. Here, we focus on the composition and function of
microbes that drive the cycling of C and N in soils and discuss the ecological sig-
nificance of their diversity and physiologies within, across, and beyond agricultural
landscapes. Compounds containing C and N are major determinants of both crop
productivity and climate change, so understanding what controls their transforma-
tions will be important for developing agricultural strategies that balance crop yield
and ecosystem services against environmental harm.
Our emphasis is on discoveries made in the past two decades at KBS LTER,
where experiments have maintained different management practices for >20 years
and aspects of C and N cycling are well documented (Robertson and Hamilton
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