Robinson Christopher Thomas
Terrestrial/aquatic linkages in microbial biodiversity in alpine floodplains: Shifting role of bacteria in ecosystem functioning (MICROLINK)
Project Number: 31003A-119735
||07/01/2008 - 06/30/2012 project completed
||PD Dr. Christopher Thomas Robinson
Aquatische Ökologie (ECO)
Phone: +41 (0) 58 765 53 17 ; +41 (0) 58 765 51 32
FAX: +41 (0) 58 765 53 15
| hydrology, limnology, glaciology|
| environmental sciences|
Genetic diversity, alpine, stream, Microbial, Stream metabolism, DGGE, T-RFLP, biodiversity, bacteria
Microbes, such as heterotrophic bacteria, are crucial in the functional ecology of terrestrial and aquatic ecosystems, beingthe driving force behind metabolic processes, nutrient retention and cycling, and trophic links with secondary consumers. Bacterialbiodiversity, including the actual genetic and functional spectrum, has only recently been investigated and knowledge about alpinelotic ecosystems and their local bacterial communities, in particular, is even scarcer. The ongoing climate-induced change inecosystems is very likely to influence bacterial communities and consequently ecosystem functioning. To what extent shifts inecosystem functioning due to future landscape transformation will be buffered by a potential resistance/resilience of bacterialcommunities is mostly unknown. Glaciated alpine floodplains provide excellent opportunities to test such fundamental ecologicalquestions as they have a high degree of insularity, biotic endemicity and are sensitive to environmental change. In addition, theselandscapes harbor structured, hydrologically interconnected and spatio-temporally heterogeneous landscape features such asdifferent stream types or interspersed lakes. These features can provide additional mechanistic understanding of how structureswithin landscapes drive biodiversity and ecosystem functioning in space and time. Such knowledge could be extrapolated to similarecosystems that potentially undergo future landscape changes induced by climate change and would improve models of ecosystemservices.
The overall aim of the present dissertation is to add to the scarce knowledge about mechanisms driving bacterialcommunity structure and function within glaciated alpine floodplains in a spatio-temporal context and to assess potential effects ofclimate induced changes within these landscapes. Several molecular biological methods, i.e. automated ribosomal intergenic spaceramplification (ARISA), catalyzed reporter deposition fluorescence in-situ hybridization (CARD-FISH) and enzymatic activity analysisin combination with a set of multivariate statistics were used to approach these questions. The first project was an extended seasonalsampling study that covered three hydrologically distinct periods and provided the large-scale context for the follow up studies. Tocover a broad range of landscape features and add more generality to this survey, we incorporated three alpine floodplains differingin geology, their degree of deglaciation, the presence of lakes, and their physico-chemical characteristics. The second chapter of thethesis focused on smaller scale landscape interactions in the context of hydrology. Piezometers that served as incubation chambersfor bacteria were installed at two locations within a glaciated valley, each representing a different array of morphological landscapestructures. Different hydrologic periods were covered to assess the importance of spatial connectivity on formation and dynamics ofbacterial communities and their related functions within riparian zone soils and in-stream hyporheic sediments. The third projectassessed the impact of potential future shifts in water sources and altered nutritional states on hyporheic sediment bacterialcommunities and functions of these aquatic ecosystems. Here, mesocosm experiments were performed in which sediments from aglacial and groundwater channel were reciprocally transplanted and nutrients added. This experiment was repeated during threedifferent seasons to cover potential temporal fluctuations within the sediment bacterial communities.
The results of the three studies revealed distinct bacterial community composition and functional differences among thecatchments and different degrees of separation in relation to structure, function and their seasonality between glacial- andgroundwater-fed stream types. Physico-chemical properties dictated bacterial structure and partially controlled their functioning. Groundwater systems were temporally more stable and showed higher degree of uncoupling between structure and function, indicating a greater prevalence of generalists. Community assemblages in the riparian zone and hyporheic sediments appeared todepend on the hydrological state of the system, thus landscape connectivity, and strategies of apparent bacterial taxa. Furthermore, the results showed that flow-mediated processes strongly influence bacterial functioning within alpine floodplains. Finally, results of transplanted bacterial communities suggest high resistance to an altered water resource or nutritional state. This was true for native glacial and groundwater communities with the latter being superior in terms of resistance. Surprisingly, there was a pronounced degree of functional plasticity/functional redundancy apparent within both bacterial communities during any season, as they quicklyadapted functionally to new environmental and nutritional conditions.
In summary, the results presented in this thesis highlight the hierarchically structured, complex and partly interconnected factors influencing bacterial communities of alpine landscapes. Bacterial communities and related functions are likely to shift inconcert with ongoing glacial retreat and the rapid changes in their eco-hydrological environment.
The primary goal of the project is to determine how changes in hydrologic connections among landscape units affect the functional and compositional response of alpine aquatic bacteria. As alpine landscapes are transformed, e.g., glacier recession and changes in vegetation, terrestrial linkages and respective water sources feeding aquatic ecosystems will change (some flowing waters will even become temporary); thereby altering ecosystem functioning and potentially affecting downstream receiving waters intensely used by humans. Specific questions to be addressed include: 1) Does bacteria biodiversity differ among alpine waters in relation to the physical-chemical characteristics of the water source and season? Presently, there is a paucity of general knowledge on microbial assemblages in alpine waters. The ecology of other organisms, e.g., aquatic macroinvertebrates, differ distinctly from their lower elevation counterparts. Bacterial abundances will be quantified using SybrGreen counts and bacteria genetic structure will be characterized using DGGE; 16S rRNA sequence analysis and CARD-FISH. 2) Is there a relationship between bacterial function and differences in water source and season? Bacteria functioning will be measured using sediment respiration, functional gene markers and CARD-FISH, esterase activity, and specific enzyme assays. Using these same measures, we will test (3) whether bacteria diversity changes along hydrologic flow paths, both lateral subsurface flow paths and larger-scale longitudinal surface flow paths. Hydrologic properties, e.g. flow paths and exchange rates, will be evaluated using standard techniques with minipiezometers and conservative tracers. -and 4) How does nutrient and carbon enrichment affect bacteria biodiversity and functioning in alpine streams with different water source? Here, field experiments using replicated flow-through chambers (mesocosms) filled with natural sediments will be used to determine the effects of nutrient enrichment (C, N, P), i.e., a change in resource quality and quantity, on bacteria biodiversity and functioning using relevant measures mentioned above. Our earlier studies have shown that nutrient enrichment increased periphyton biomass and leaf decomposition rates, while also altering the response of invertebrates to disturbance. The overall study will involve both comparative analysis and field experiments to answer the proposed questions. The comparative assessment provides the context and justification for experiments intended to reveal mechanistic connections and underlying causes of patterns.
Freimann Remo 2012: Microbial Diversity in Alpine Floodplains: Spatio-Temporal Factors Influencing Bacterial Communities and Ecosystem Functioning. Dissertation ETH Nr. 20420
Freimann R, Bürgmann H, Findlay S E G, Robinson C T (2013) Response of lotic microbial communities to altered water source and nutritional state in a glaciated alpine floodplain. Limnol. Oceanogr., 58(3), 2013, 951–965. Copyright 2013, by the Association for the Sciences of Limnology and Oceanography, Inc.
Last update: 12/23/16
Source of data: ProClim- Research InfoSystem (1993-2020)
Update the data of project: CH-3850