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different taxonomic levels or functional grouping showed that family and trophic group
composition were closely related to each other ( Figure 5.5 ) . However, community composi-
tion patterns observed at the species level or by wing morphology type did not resemble
family or trophic group composition.
5.3 Discussion
Based on diversity indices, we did not observe significant differences between the four
farming systems; however, community composition differed significantly for two of the
five analyzed groups of soil organisms. FA profiles of microorganisms and nematode
community composition showed distinct patterns separating communities in the farming
system that only received synthetic fertilizer (CONMIN) from communities of the three
systems that received manure.
Biomarker FAs for gram-negative bacteria (18:1ω7) and AMF (NLFA 16:1ω5) both had
higher concentrations in organically managed fields. Moeskops et al. (2010) observed simi-
lar responses by biomarker FAs for AMF comparing organic versus conventional horti-
cultures and concluded that the high sensitivity of this group was related to a reduced
colonization potential of AMF (see also Bending et al. 2004) and a lower inoculum (see
also Mäder et al. 2002) in conventionally managed fields. According to Peacock et al. (2001),
gram-negative bacteria suffer from the application of inorganic fertilizers and increase
in concentration under application of manure. Organic substrates promote the growth of
gram-negative bacteria, and the pronounced differences in the availability of organic car-
bon in our study system most likely contributed to the observed pattern (see also Bossio
and Scow 1998). The patterns of FA profiles in the four farming systems supported the gen-
eral trends for a dominance of gram-positive bacteria and a reduction of fungal biomass
in conventionally managed systems (see also Gryndler et al. 2006; Esperschütz et al. 2007).
Nematode communities showed a significant, but more complex, response to farming
systems compared to FA profiles. The abundance of individuals from the genus Tylenchus
contributed to a separation of the NPK-only (CONMIN) treatment from other farming
systems. Tylenchus is known to feed on root hairs or hyphae (Thorne 1961), and the appli-
cation of herbicide prior to our sampling followed by reduced weed presence may have
contributed to the lower abundance of this species in conventionally managed systems.
Population sizes of this species were higher under the application of manure compared to
NPK fertilizer (Liang et al. 2009), and our results suggest that the addition of organic sub-
strates promotes Tylenchus densities. Individuals from the genus Rhabditis were only found
in the system that received synthetic fertilizer and manure (CONFYM) but were absent
from the two organically managed systems and the system that only received synthetic
fertilizer. Bacterivorous nematodes generally benefit from the application of compost or
manure and have lower abundances in fields that are only treated with synthetic fertil-
izers (Hu and Qi 2010), but it remains unclear why this genus was absent from organically
managed fields. At the family level, the single genus within the family Aphelenchidae
( Aphelenchus sp.), which are fungal feeders, was absent from the biodynamically managed
fields, and individuals from the family Anguinidae had higher abundances in fields that
received manure. Populations of Aphelenchus sp. have been shown to benefit from cultiva-
tion (mechanical weed management) but to suffer from organic mulching (Wardle et al.
1995). Addition of organic substrate may have contributed to the observed lower abundance
of this genus in biodynamically managed plots, but it remains unclear why individuals
from this genus did not show a similar response in bioorganic fields. Individuals from the
genus Ditylenchus (Anguinidae) most likely belong to the fungal-feeding guild. As fungal
 
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