Soil Teeming with Life: New Frontiers for Soil Science - Sustainable Management of Soil Organic Matter - page 413

soils, and this was inversely related to the metabolic quotient of the soil
microbial biomass. However, they did not find significant effects in the
quality of the soil organic matter, measured by 13 C-NMR. O'Flaherty et al .
showed that metal-rich sludges applied to land, which might otherwise have
been assumed to cause stress and a reduction in diversity, actually increased
diversity (measured using molecular methods). Clearly, simple generaliza-
tions may be hard to come by.
Several papers have quantified functional diversity (Fliebßach et al .,
O'Flaherty et al . and Degens) and attempt to relate the quality of organic
matter and/or changes in land use to diversity. Fleibßach et al . and
O'Flaherty et al . tested soil extracts using Biolog plates to construct
community-level physiological profiles (CLPPs), while Degens has
pioneered the use of whole-soil substrate-induced respiration methods to
produce catabolic response profiles (CRP). There is still debate on how
well such methodologies measure functional diversity. Both approaches
measure the potential utilization of different carbon sources at relatively
high levels of C amendment, but clearly the functional approach is seen as a
useful way to gain new insight.
Biological indicators of soil health should ideally be rapid and sensitive
but there also needs to be a substantive amount of background information
on natural variation and what constitutes 'normal' responses before value
judgements can be made. Degen's use of catabolic diversity as a generic
indicator of changes in soil functioning due to land use and the application
of wastes to soil is a case in point. If rapid methods could be found for
measuring such parameters, then this is an approach that might be
attractive to agencies that have to monitor and regulate soil protection
policies. The vision of the future presented by Tiedje et al . suggests that
functional genomics will eventually allow us to measure important
functional attributes, possibly at the mRNA level, so that the limitations of
the potential measures and culturability will one day be overcome.
What then, after we have fully quantified this diversity? How do we
then manage or manipulate it to create a more sustainable system? The
ability to manage soils to enhance key species such as earthworms (Scullion
and Malik) or rhizobium is clearly an advantage. Microbial communities
might in the future be managed for environmental protection as well as
to enhance nutrient supply. For example, organic matter (sawdust) added
in trenches adjacent to streams has be used to stimulate denitrifying
organisms and create a 'denitrification wall' to protect waters from excess
nitrate (Schipper and Vojvodic-Vukovic, 2000). Thus management of key
functional groups or species responsible for key processes is arguably quite
realistic, but how to manage the more complex generalist communities?
The importance of the rhizosphere as the interface between plant-soil-
microbial interactions (de Neergaard and Magid) is also now realized
and research is being directed at 'rhizosphere engineering' to achieve, for