Implications of Soil Biodiversity for Sustainable Organic Matter Management - Sustainable Management of Soil Organic Matter - page 353

pine forestry, indigenous vegetation and mixed pasture-cropping with
long-term pasture (as a reference land use) have shown that losses in
soil organic C (relative to pasture) corresponded with losses in catabolic
evenness (Fig. 5.1.1), i.e. where a land use results in less organic C relative
to pasture, there was also a corresponding lower catabolic evenness in
this land use. The same relationships did not apply to measures of more
active organic C fractions in soils (microbial biomass C or potentially
mineralizable C; Degens et al ., 2000b). These comparisons used long-term
pasture as a reference land use because this frequently is readily obtained on
most soil types. Since most soils under pasture and indigenous vegetation
had similarly high levels of catabolic evenness (above), soils where catabolic
evenness is less than this are most likely to contain amounts of organic C
that are constrained by previous management practices.
Catabolic evenness responds positively to organic matter inputs
into soils. Application of 5 t ha −1 of organic matter as sewage sludge to a
sandy soil increased catabolic evenness from 22.8 to 23.1 ( P < 0.05, n = 3).
Repeated additions of large amounts of organic C with a narrow substrate
composition can result in reductions in catabolic evenness over the long
term. In a study of soil irrigated with large amounts of lactose (as dairy
factory effluent), catabolic evenness had declined from 21.9 in non-
irrigated soil to 19.4 ( P < 0.05, n = 6) in the irrigated soil. This occurred
principally because of much greater response to both lactose and glucose in
the irrigated soil (Degens et al ., 2000a). Greater catabolic evenness may be
an indicator of greater substrate diversity in soils.
Conclusions
Microbial catabolic diversity presents an alternative tool for monitoring
soils to detect adverse impacts of land use systems on soil biological
condition. This approach is based on the premise that the presence of an
active and diverse microbial community in soil can be considered a good
indicator of a healthy and functioning soil ecosystem. The catabolic
evenness index provides a versatile indicator to compare the impacts of a
range of land uses and organic matter management strategies on different
soil types. Furthermore, the index may be useful in discriminating sites
where the organic C status of soils is under pressure from previous land use,
without extensive knowledge of land use history or needing to compare with
benchmark sites on matched soil types. This characteristic of the catabolic
evenness index makes the indicator potentially useful as a generic indicator
of the impact of land use on soil organic C status and biological condition.
Microbial catabolic diversity provides information on the diversity
component of soils that is not encompassed within measures of the
sizes of organic C pools such as total organic C, microbial biomass C or