Identification of keystone prokaryotic food web members and links in belowground carbon turnover - SP MicLink
Soil Sciences
Final Report Abstract
Microorganisms control the turnover, fate and mineralisation of organic carbon in soil and are at the foundation of food webs in soil. A detailed understanding of microbial populations and trophic interactions involved is needed for a more comprehensive grasp of terrestrial carbon cycling. The DFG Research Unit FOR-918 “Carbon flow in belowground food webs assessed by isotope tracers” has generated such integrated understanding for the food web of a representative agricultural soil system, across all trophic levels involved. Within FOR-918, this subproject “MicLink” has identified and quantified specific bacterial populations involved in distinct carbon flows of the investigated food web. This is an important prerequisite for a more advanced population-based conceptual understanding and modelling of belowground carbon flows. In a series of synchronised stable isotope probing (rRNA-SIP) experiments, conducted either by SP MicLink or together with other SPs of the Research Unit, bacterial carbon flows in the rhizosphere, detritusphere and within intra-microbial food webs of the soil were investigated. We show that in contrast to previous assumptions, the flow of fresh 13C-labelled plant assimilates mediated by arbuscular mycorrhizal fungi (AMF) to distinct Verrucomicrobia, Planctomycetes and other bacteria in the so-called hyphosphere of the investigated soil was more rapid and pronounced than direct exudation to typical rhizosphere bacteria associated to the roots. Furthermore, carbon flow from both labile and recalcitrant detritusphere substrates involved a pronounced activity of distinct bacteria and fungi, thus rejecting the hypothesis of separate bacterial and fungal energy channels for the investigated soil. Finally, intrabacterial-predation by Myxobacteria was shown to be pronounced for Gram-negative bacterial prey and in the rhizosphere, while protozoan micropredators were less prey-selective and active also in bulk soil. Thus, an importance for predatory bacteria in the microbial loop was revealed especially for the rhizosphere, calling for a revision of microbial food web comprehension. Seepage water collected in lysimeters after rainfall and snowmelt was investigated to study a largely neglected efflux mechanism for microbes and microbial carbon from top soil. For the first time, seepage water was shown to mobilise a distinct subset of mostly root-associated bacteria, suggesting preferential water flow along root channels to control their mobilization. This represents a previously unidentified direct link between top soil and subsoil microbiota, while at the same time, associated C-fluxes were relatively small. The distribution of total bacterial populations in the field was mostly affected by soil compartment and depth. In contrast to fungi, the effects of experimental treatments (plant type, litter) on overall bacterial community structures were negligible. However, significant effects of plant and litter treatments on total bacterial abundance were readily observed, with bacterial gene counts being highest in wheat + litter, and lowest in fodder maize treatments, respectively. Thus for microbes, impacts of food web functioning may be more apparent via the abundance of keystone populations, rather than community structure. These fundamental insights into the microbial components of a selected belowground food web illustrate that bacteria are not yet adequately incorporated in current food web concepts. Complex successions, inter-kingdom feedback mechanisms and spatial links between metacommunities need to be considered to evolve the largely static interaction networks in current food web modelling.
Publications
- (2011). Towards an improved understanding of trophic connectivities in belowground microbial food webs. VAAM, Karlsruhe
Dibbern, D., Lueders, T.
- (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.
(See online at https://doi.org/10.1016/j.soilbio.2012.03.002) - (2012). Selective mobilisation of rhizosphere bacterial populations upon groundwater recharge. ISME, Seoul
Lueders, T., Dibbern, D., Schmalwasser, A., Totsche, K.U.
- (2013). Selective vertical mobilisation of microbes in agriculture soils after rainfall. VAAM, Bremen
Zhang, L., Dibbern, D., Schmalwasser, A., Totsche, K.U., Lueders, T.
- (2014). 5-year tracking of overall soil bacterial communities and keystone bacteria involved in plant-derived carbon in a maize field. VAAM 2014, Dresden
Zhang, L., Dibbern, D., Lueders, T.
- (2014). Selective transport of plant rootassociated bacterial populations in agricultural soils upon snowmelt. Soil Biology Biochemistry 69, 187-196
Dibbern, D., Schmalwasser, A., Lueders, T., Totsche, K.U.
(See online at https://doi.org/10.1016/j.soilbio.2013.10.040) - (2015). Transport of plant-associated bacterial populations in an agriculture soil upon rainfall. VAAM 2015, Marburg
Zhang, L., Lueders, T.
- (2016). Resource partitioning between bacteria, fungi, and protists in the detritusphere of an agricultural soil. Frontiers 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.
(See online at https://doi.org/10.3389/fmicb.2016.01524)
