| dc.description.abstracteng | Present day agriculture is identified as a main threat to biodiversity. At the same time, the productivity
of agricultural systems is relying on ecosystem services provided by biota. In order to conserve critical
ecosystem services for future generations preserving the functions of the soil is one main goal of
sustainable agriculture. Nevertheless, the impact of management practices on soil biota providing
critical ecosystem services remains ambiguous. The high level of complexity in combination with
limited taxonomic knowledge and the opaqueness of the soil hampers general conclusions. To develop
sustainable management practices a better understanding of how farm-based management practices
shape soil biota communities is needed. Thereby, trait based approaches can be used to increase
mechanistic understanding while at the same time circumvent time consuming species identification.
In the present thesis we utilized trait based approaches to assess effects of farm-based management
practices on Collembola communities.
In Chapter 2 we investigated how Collembola communities are affected by reduced tillage in
comparison to conventional tillage practices. We evaluated Collembola communities in five long-term
tillage field trials across European countries (Sweden, Germany, France, Romania and Spain). The study
included differing bioclimatic regions to assess general effects of agricultural practices on soil
Collembola across Europe. We found different ecological groups of Collembola defined by
morphological traits to be differentially affected. Epedaphic Collembola were detrimentally affected
while especially euedaphic Collembola were fostered by conventional tillage. Further, we found
Collembola communities to be differentially affected depending on the dominating ecological groups
at each field site. Reactions of Collembola communities resembled effects of tillage practices on
organic carbon and total nitrogen revealing similar changes in depth distributions. Our results suggest
nutrient supply in terms of organic carbon and total nitrogen in combination with favourable soil
moisture conditions to be of critical importance for soil Collembola. The displacement of litter
resources by tillage into deeper soil where they are available under preferable moisture conditions
turned deeper soil layers into habitable space utilized especially by euedaphic species.
In Chapter 3 we investigated the effect of Collembola and tillage on litter decomposition. We
conducted a litterbag experiment in a long-term tillage field trial in Germany with reduced and
conventional tillage. We buried litterbags filled with maize litter at the respective depth of tillage.
Further, we investigated the incorporation of litter derived carbon into Collembola to quantify their
dependence on litter resources under different tillage regimes. Collembola promoted decomposition
by enhancing carbon loss and the transformation of litter into high quality resources as indicated by
C/N ratios. Conventional tillage favoured colonization of litterbags by Collembola, especially that of
euedaphic species. Furthermore, in conventional tillage fields Collembola depended more on litter
material than in reduced tillage fields. In conclusion, Collembola accelerate litter transformation by
increasing carbon loss and nitrogen accumulation. Facilitative effects on nitrogen capture from
decomposing litter material by crops may contribute to the sustainability of arable systems.
In Chapter 4 we investigated the effect of intercropping and genetic variation of crop species on
Collembola communities. We sampled Collembola communities in two field trials in Germany
containing monocultures of four genotypes of faba bean and intercropped stands of each genotype
with winter wheat. The field sites differed in soil carbon and nitrogen content. Intercropping only
promoted Collembola in the low carbon field site, but the effects were restricted to hemiedaphic
Collembola while eu- and epedaphic Collembola remained unaffected. Further, at the low carbon site
Collembola benefited from the bean genotype characterized by high tillering and short shoots which
yielded the highest root biomass. The results suggest that root and shoot overyielding in intercropped
stands led to increased availability of carbon resources for Collembola. Our results indicate that
intercropping and the choice of plant genotypes promote Collembola communities if resources are
scarce. Presumably the beneficial effects are mediated by the provision of litter and root resources
and improved moisture conditions as well as habitat diversification.
Overall, the results of Chapters 2 and 4 indicate the availability and quality of resources in combination
with preferable moisture conditions to be of critical importance for Collembola. These abiotic factors
determine habitat suitability and they surpass the importance of mechanical disturbance and soil
compaction. Results of Chapter 3 highlighted the dependency of Collembola on litter resources in
agricultural systems. In addition, it proved that Collembola accelerate litter decomposition thereby
contributing to crucial ecosystem services. Altogether, the results of this thesis indicate that the
response of Collembola to farm-based management practices depend on underlying changes in abiotic
conditions. Generally, we showed the suitability of trait based approaches as tool to improve
mechanistic understanding of the response of Collembola communities to farm-based management
practices, which is urgently needed for the sustainable management of arable systems. | de |