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non-competitive diversity pattern observed in surface soils (Fig. 6.2), and
suggest that even in a highly uniform large-particle matrix, such as sand, the
impact of spatial isolation appears dramatic. One would predict that in
smaller particle matricies such as soil these spatial isolation effects would be
experienced even more readily.
Although simple, the two-species microcosm design is remarkably
flexible. They should allow us to tease apart the contributions that spatial
isolation and resource heterogeneity make to the maintenance of microbial
diversity. The results hopefully will shed some light on how factors such as
soil particle size, total organic carbon and clay content of soils impact on
microbial diversity.
Are Soil Heterotrophic Communities Geographically
Unique?
The soil matrix that maintains diversity can also promote an ongoing
diversification if the rate of local genetic change exceeds the rate of microbe
dispersal. The dogma in the past has been that microbes, being small, are
readily transported globally by wind, birds and human activity to name the
most likely. This implies that the microbes inhabiting the Edinburgh valley
soils are the same as those inhabiting Michigan and New Zealand valley
soils. Is this true? The question has not been seriously addressed. Until the
development of molecular tools, we did not have a means for realistically
addressing microbial biogeography. Most countries have quarantine
systems directed against spread of plant pathogens, but these organisms are
usually host-associated organisms in their growth habitat, not free-living
heterotrophic soil bacteria. Hence, the experience from quarantine is
not
particularly
helpful
for
resolving
the
question
of
soil
microbial
biogeography.
The question of whether soil microbes are basically cosmopolitan
(everywhere) or endemic (geographically unique) has important implica-
tions. If endemic, the estimate of global microbial diversity expands
tremendously. The answer has important implications for strategies for
discovery of new biotechnology products and for national intellectual
property rights. Furthermore, if endemism predominates, it means that soil
microbial process information is not transported so reliably between differ-
ent geographic locations. We have addressed the question of whether soil
heterotrophic bacteria are endemic with two types of bacterial populations,
one set selected on the member's ability to degrade 3-chlorobenzoic acid
(3-CBA), a rare property in nature, and the other a coherent taxonomic
group, the fluorescent Pseudomonas .
Our strategy was that the major ecological features influencing bacterial
selection should be the same at least within ecosystem type, i.e. climate, soil
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