Community composition of soil organisms under different wheat-farming systems - Microbial Ecology in Sustainable Agroecosystems - page 104

The second-stage NMDS relates several multivariate patterns to each other to help
identify if taxonomic sufficiency is a valid concept in studying community-level responses
to agricultural management. Figure 5.5 suggests that only limited additional information
is gained from higher taxonomic resolution comparing patterns within taxa but between
different taxonomic or functional resolutions. Nevertheless, compositional data on indi-
vidual FA concentrations and nematode genera provided a significant separation of organic
systems from systems that received either manure and NPK or only NPK fertilizers. Such
detailed contrasts were lost if community composition was analyzed at coarser resolu-
tions. From such results, it remains unclear if the critical comment about the informa-
tion loss caused by aggregating data into more or less arbitrary formed higher taxonomic
orders (Bertrand et al. 2006) is supported by our analyses. However, it seems plausible that
information could be lost after aggregation as individuals in higher-order categories have
less-well-defined ecological niches and therefore may not show a pronounced response to
anthropogenic disturbance. Functional groups are defined at different taxonomic resolu-
tions (e.g., nematode at genus level, spiders at family level, and carabids at species level)
and include different information about community-level responses to disturbance. In our
case study, nematode and carabid patterns in functional group composition contained dif-
ferent information compared to patterns observed at the highest possible taxonomic reso-
lution. Báldi (2003) suggested that richness patterns at higher taxonomic orders are well
correlated with species richness patterns for some terrestrial arthropod groups. However,
this approach to taxonomic sufficiency only holds true if research solely focuses on rich-
ness measures. As soon as multivariate community responses are within the focus of a
study, aggregation into higher taxonomic levels or functional groups almost certainly
changes the information content (see also Maurer 2000). In such cases, different species/
genera fall within the same functional groups, and the resulting multivariate patterns in
functional group composition may therefore not resemble taxonomic composition.
We conclude that a low-level taxonomic resolution in soil organisms often provides
more detailed and ecologically meaningful information about response patterns of com-
munities to anthropogenic disturbance. Our case study particularly highlighted the added
value of genus-level nematode determination and individual FA data for identifying dif-
ferences between organic and conventional wheat-farming systems. However, additional
multivariate analyses of functional group composition are important if functional groups
can be built without resembling taxonomic groups too closely.
References
Acosta-Martinez, V., M.M. Mikha, and M.F. Vigil. 2007. Microbial communities and enzyme activities
in soils under alternative crop rotations compared to wheat-fallow for the Central Great Plains.
Applied Soil Ecology 37:41-52.
Adl, S.M. 2003. The Ecology of Soil Decomposition . CABI, Wallingford, UK.
Alvarez, R. 2005. A review of nitrogen fertilizer and conservation tillage effects on soil organic carbon
storage. Soil Use and Management 21:38-52.
Andersen, A.N., B.D. Hoffmann, W.J. Muller, and A.D. Griffiths. 2002. Using ants as bioindicators
in land management: simplifying assessment of ant community responses. Journal of Applied
Ecology 39:8-17.
Anderson, M.J., R.N. Gorley, and K.R. Clarke. 2008. PERMANOVA+ for PRIMER: Guide to Software
and Statistical Methods . PRIMER-E, Plymouth, UK.
Avery, A. 2007. “Organic abundance” report: fatally flawed. Renewable Agriculture and Food Systems
22:321-323.