Nematodes as link between microbial and faunal food web
Final Report Abstract
Within the framework of the Research Unit “Carbon flow in belowground food webs assessed by isotope tracers” the project NemWeb examined the nematode fauna at the two common field experiments “Long-term recalcitrant C input” and “Carbon flow via the herbivore and detrital food chain”. A gradient from resource rich to deeper oligotrophe habitats, i.e. from high to low diverse food webs, was investigated. The impact of resource availability and quality (recalcitrant versus labile) and presence or absence of living plants (rhizosphere versus detritusphere) was assessed. Insight into the micro-food web was gained by application of the nematode faunal analysis concept (e.g. enrichment, structure and channel index) and by using nematode biomass as proxy for carbon flow. The nematode fauna was not homogenously dispersed across the depth profile, and rather located in spatially separated patches comprising different metacommunities. The strongest abiotic factor was soil depth, followed by crop type, while effects of litter amendment were less pronounced. Transport processes of organic matter crossed community boundaries, linking top soil and subsoil, notably in periods without a crop. Nematode biomass distribution of families and trophic groups implied a higher predation pressure in the rooted zone compared to top soil, predominance of bottom-up control in the root and of top-down forces in the fungal energy channel. Removal of plants from the system had less severe effects than expected, suggesting considerable food web resilience to the disruption of the root carbon and energy channel and pointing to a legacy of organic matter resources in arable soils. In labelling experiments in the field (13C) and laboratory (14C, 13C) the carbon pools, fluxes and budget within the nematode micro-food web were determined. These revealed a major dominance of the fungal energy channel for the transfer of plant carbon into belowground food webs, which contradicts the common opinion of a dominance of the bacterial channel in arable soils. In laboratory model systems carbon flux rates for food web links were determined between bacteria or fungi and their nematode grazers for taxa frequent in the arable field. To use 13C/12C fatty acid stable isotope probing (FA-SIP) as major carbon currency, a MS technique (isotopologue profiling) was developed that accounts for the conditions in the soil micro-food web, i.e. low biomass and specific fatty acids markers. In sum the project NemWeb, by connecting the microbial and faunal food web, contributed significantly to the major goals of the Research Unit. Combining nematode community composition with biomass and 13C allocation allowed to directly linking nematode functional groups with specific processes in the soil carbon cycle. Application of advanced techniques for 13C bulk analyses in nematodes provided first empirical carbon flux data for the micro-food web in the field, whereas the new developed isotopologue profiling for 13C/12C quantification in fatty acids allowed new insight in consumer carbon allocation from specific diets. Overall, coupling the qualitative and quantitative data gathered for soil nematode communities will provide a profound basis for future soil food web modelling.
Publications
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(2012). Carbon flow into microbial and fungal biomass as a basis for the belowground food web of agroecosystems. Pedobiologia 55, 111-119
Kramer, S., Marhan, S., Ruess, L., Armbruster, W., Butenschoen, O., Haslwimmer, H., Kuzyakov, Y., Pausch, J., Scheunemann, N., Schoene, J., Schmalwasser, A., Totsche, K.U., Walker, F., Scheu, S., Kandeler, E.
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(2012). Effects of resource availability and quality on the structure of the micro-food web of an arable soil across depth. Soil Biology and Biochemistry 50, 1-11
Scharroba, A., Dibbern, D., Hünninghaus, M., Kramer, S., Moll, J., Butenschoen, O., Bonkowski, M., Buscot, F., Kandeler, E., Koller, R., Krüger, D., Lueders, T., Scheu, S., Ruess, L.
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(2013). Temporal variation in surface and subsoil abundance and function of the soil microbial community in an arable soil. Soil Biology and Biochemistry 61, 76-85
Kramer, S., Marhan, S., Haslwimmer, H., Ruess, L., Kandeler, E.
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(2014). Veränderung der Nematodengemeinschaft beim Wechsel des Nahrungskettentyps. Arbeitskreis Nematologie, Görlitz
Glavtaska, O., Ruess, L.
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(2015). Resource quality and availability regulate fungal communities in arable soils across depth. Microbial Ecology 70, 390-399
Moll, J., Goldmann, K., Kramer, S., Hempel, S., Kandeler, E., Marhan, S., Ruess, L., Krüger, D., Buscot, F.
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(2016). Fluxes of root-derived carbon into the nematode micro-food web of an arable soil. Food Webs
Pausch, J., Hofmann, S., Scharroba, A., Kuzyakov, Y., Ruess, L.
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(2016). Incorporation of root C and fertilizer N into the food web of an arable soil: Variations with taxonomic and trophic position. Food Webs 9, 39-45
Scheunemann, N., Pausch, J., Digel, C., Kramer, C., Scharroba, A., Kuzyakov, Y., Kandeler, E., Ruess, L., Butenschoen, O., Scheu, S.
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(2016). Small but active – pool size does not matter for carbon incorporation in below-ground food webs. Functional Ecology 30, 479-489
Pausch, J., Kramer, S., Scharroba, A., Scheunemann, N., Butenschoen, O., Kandeler, E., Marhan, S., Riederer, M., Scheu, S., Kuzyakov, Y., Ruess, L.
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(2016). Spatial and temporal variation of resource allocation in an arable soil drives community structure and biomass of nematodes and their role in the micro-food web. Pedobiologia 59, 111-120
Scharroba, A., Kramer, S., Kandeler, E., Ruess, L.
