The bacterial energy channel: Protozoa-bacteria interrelationships as affected by root vicinity, organic matter and soil depth
Soil Sciences
Final Report Abstract
The project investigated the carbon flux through the bacterial channel of the decomposer food web. As basis the density and community structure of Protozoa along two gradients of a maize field were investigated: (1) in maize rhizosphere and detritusphere and (2) from upper to deeper soil layers. Methodological improvements during the project forced us to repeated changes of the methods. Although this prevented long-term comparisons, the taxonomic resolution dramatically improved. The treatment effects of the field experiments were not as strong as we anticipated them to be. A decreased abundance with depth was not surprising, but we found distinctly different communities at different soil depth. A surprisingly rich protist community below the plough zone suggests strong predator-prey interactions in deep soil layers. We manipulated protozoan diversity in the detritusphere and found a significant increase of microbial mineralization, but no clear diversity effect. Instead a succession of protozoan grazers controlled microbial respiration during litter decomposition. Especially the results of experiments applying stable isotope probing led to intense discussions and changed our perception of microbial interactions. We could not find clearly separated fungal and bacterial energy channels in the detritusphere. In the rhizosphere mycorrrhiza translocated a significant amount of root-C into bulk soil. Most importantly for us, the data revealed completely new and often unexpected results on protist functions in soil. Protists are functionally highly diverse, and our data indicate important roles of fungal feeders and saprotrophs (oomycetes). Especially the latter turned out to be highly competitive foragers for low-molecular weight carbon both in the rhizosphere and the detritusphere.
Publications
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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 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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(2016). A novel lineage of ‘naked filose amoebae’; Kraken carinae gen. nov., sp. nov. (Cercozoa) with a remarkable locomotion by disassembly of its cell body. Protist 167, 268-278
Dumack, K., Schuster, J., Bass, D., Bonkowski, M.
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(2016). Description of Lecythium terrestris sp. nov. (Chlamydophryidae, Cercozoa), a soil dwelling protist feeding on fungi and algae. Protist 167, 93-105
Dumack, K., Muller, M.E., Bonkowski, M.
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(2016). Resource Partitioning between Bacteria, Fungi, and Protists in the Detritusphere of an Agricultural Soil. Frontiers in Microbiology 7, 1524
Kramer, S., Dibbern, D., Moll, J., Huenninghaus, M., Koller, R., Krueger, D., Marhan, S., Urich, T., Wubet, T., Bonkowski, M., Buscot, F., Lueders, T., Kandeler, E.
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(2016). The soil food web revisited: Diverse and widespread mycophagous soil protists. Soil Biology Biochemistry 94, 10-18
Geisen, S., Koller, R., Hünninghaus, M., Dumack, K., Urich, T., Bonkowski, M.
