Implications of Soil Biodiversity for Sustainable Organic Matter Management - Sustainable Management of Soil Organic Matter - page 338

Experimental Approaches
Studies into the relationships between biodiversity and function require
the effective experimental control of biodiversity factors, preferably in
replicated systems that also permit function to be measured appropriately.
This can be achieved in four ways:
1. Constructive approaches . Sterile systems are established and prescribed
levels of biodiversity built up by the addition of appropriate organisms. The
inocula may be comprised of individual species with precisely known
characteristics, or may be a less well characterized community of individu-
als derived from natural habitats. Problems with this approach include the
difficulty of establishing slow-growing K strategists, since R strategists will
tend to prevail. Building up 'realistic' levels of diversity, particularly in the
microbial pool, is also very difficult due to the apparent non-cultivability of
many soil prokaryotes and the naturally high levels of diversity in this
component.
2. Deconstructive approaches . An alternative way to alter diversity is to
treat soils in such a way that prescribed groups are selectively removed or
destroyed. This can be achieved by application of selective biocides, or
based on size exclusion by filtration, sieving or mesh-lined containers.
3. Correlative approaches . Natural gradients in diversity can be exploited by
taking soils that have inherently different levels of diversity and measuring
their functional characteristics. This approach has the drawback that
correlation does not necessarily imply cause, and does not offer much
possibility of gaining a mechanistic understanding for observed effects. It
also represents poor experimental design in that there are likely to be many
additional covariates that may confound any diversity effects.
4. Modelling . Mathematical models offer a supplementary way of explor-
ing the functional consequences of biodiversity. Models are an experimen-
tal tool and require real data for their calibration and validation as well as
the concepts that underpin their formulation. Models are best developed
in tandem with rigorous experimentation. Most soil-based models that
do include diversity elements deal with trophic-level diversity and do not
explicitly incorporate intra-group diversity. Indeed, many process models
have predicted SOM dynamics successfully without any recourse to the
inclusion of species diversity or abundance dynamics. Andrén et al . (1999)
review this field and argue that the soil biota can often be regarded as an
'averaging engine', making the analogy of the ecosystem as a gas container.
Thus average processes are observed or measured and the contributions of
the individual organismal components are filtered out. They also discuss
circumstances when this approach may be insufficient.
Some selected examples of the application of these approaches to study
the effects of soil biodiversity upon OM dynamics are described below.