Agriculture Reference
In-Depth Information
biomass is highest in the organically managed systems of the DOK trial (see Birkhofer,
Bezemer, et al. 2008), the increased abundance of this genus probably reflects the higher
availability of resources. It further remains unresolved why one family of fungal-feeding
nematodes (Anguinidae) benefits from higher fungal biomasses, whereas another family
from the same trophic group does not show such response to high-fungal biomasses in the
biodynamically managed plots (Aphelenchidae).
It has been suggested that agricultural intensification will have a stronger impact on
the abundance and diversity of larger (enchytraeids and nematodes) versus smaller taxa
(bacteria and fungi; Postma-Blaauw et al. 2010); however, this was not present if commu-
nity composition was considered in our study. Our results suggest that community com-
position of taxa with larger body sizes (Enchytraeidae, Araneae, and Carabidae) did not
respond significantly to differences in farming systems. The abundance and species rich-
ness of smaller soil organisms may suffer more from anthropogenic disturbances, com-
pared to larger, surface-active arthropod taxa (Dauber et al. 2005; Birkhofer, Bezemer, et
al. 2008). In soils, however, the suggested stronger impact of agricultural intensification on
the abundance and diversity of larger (enchytraeids and nematodes) versus smaller taxa
(bacteria and fungi; Postma-Blaauw et al. 2010) was not present if community composition
was considered in our study. In contrast, our results suggest that bacterial, fungal, and
nematode community composition responded stronger to intensified farming practices
than larger endogaeic (enchytraeids) or epigeic (spider or ground beetle) communities. In
summary, we therefore suggest that less-mobile, soil-living species either may be affected
more seriously by intense management or may fail to recolonize disturbed fields as suc-
cessfully as larger, more mobile taxa.
Relating patterns of soil organism communities to the observed resemblance of plots in
terms of soil properties or ecosystem functions suggests that less-mobile, endogaeic organ-
isms (bacteria, fungi, and nematodes) closely resemble multivariate patterns observed
for soil properties and ecosystem functions. In contrast, the community composition of
enchytraeids, carabids, and spiders did not resemble the similarity between plots based on
soil and functional characteristics. Endogeic taxa are probably more seriously affected by
agricultural management (see previous section), and such agricultural intensification also
directly alters soil properties. Indirect effects of agricultural management on soil organ-
isms include the alteration of habitat structure (e.g., Blackshaw et al. 2003) or soil biotic
conditions (e.g., Haynes and Naidu 1998). It is therefore likely that multivariate patterns in
soil properties and community composition of soil organisms are linked to each other and
to management practices.
The observed close relationship between field-specific functional parameters, commu-
nity composition in nematodes, and FA profiles at least partly reflects the assumed linkage
between N content in wheat plants, N mineralization rates, abundance of bacterivorous
nematodes, and bacterial activity. Bouwman and Zwart (1994), for example, demonstrated
that grazing through nematodes promotes bacterial activity and therefore alters rates of
N mineralization (see also Bloem et al. 1994). Populations of some nematode families can
even be limited by the availability of bacteria in agricultural soils (Bouwman and Zwart
1994). Our observation that patterns in nematode community composition resemble pat-
terns for the composition of bacterial and fungal communities supports the assumption of
close interactions between bacterial and fungal resources and consumers at higher trophic
levels. We further demonstrated that not only the abundance of nematodes or bacteria
relate to the quantified ecosystem functions but also observed close relationships between
management practices, community composition of nematodes, FA profiles, and multivari-
ate patterns in ecosystem functions.
Search WWH ::
Custom Search