Pioneer communities in the forefields of retreating glaciers: how microbes adapt to a challenging environment Lazzaro A, Franchini AG, Brankatschk R, Zeyer J Environmental Microbiology, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Universitätstrasse 16, 8092 Zurich, Switzerland 1. Introduction Glacier forefields are the landscape formed by retreating glaciers. As a glacier melts down, bare rock and gravel that have been covered by the glacier are released. This material is then subjected to weathering and to soil forming processes. The young soils characterising glacier forefields are generally scarcely vegetated and low in nutrients such as C, N, P and S. Bedrock properties determine the physico-chemical properties of the corresponding soils such as texture, pH, nutrient concentrations, heat and humidity retention, water and gas fluxes. Moreover, they are characterized by strong physical extremes, in particular concerning temperature and water regimes. Such conditions may also vary locally. Site morphology and slope orientation, for example, may be related to different precipitation and irradiation. The climate at glacier forefields is generally highly variable: for example, precipitation tends to be more frequent in spring and in autumn; winters are instead characterized by heavy snowfall, which melts relatively fast in spring. Strong day-night fluctuations in soil temperatures are also often observable [1]. The colonization of the exposed bedrock by pioneer microorganisms which can well adapt to the low nutrient conditions and climatic fluctuations is the first step in soil development (Fig. 1). Pioneer microorganisms are involved in all the major biogeochemical cycles, contribute to mineral weathering and subsequent release of nutrients [2], which in turn favours the establishment of more complex and efficient microbial communities and plants [3]. Microbial communities are therefore vital for the initiation and maintenance of nutrient cycling and ecosystem productivity. In soil, 80-90% of soil function is provided by microbes [4]. Fig. 1. Schematic representation of components (white boxes) and processes (black boxes) the forefield of a retreating glacier. The white arrows represent possible origins of the pioneer communities (below glacier, above glacier, from the surroundings) _______________________________________________________________________________________
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Pioneer communities in the forefields of retreating glaciers: how microbes
adapt to a challenging environment
Lazzaro A, Franchini AG, Brankatschk R, Zeyer J
Environmental Microbiology, Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, Universitätstrasse 16,
8092 Zurich, Switzerland
1. Introduction
Glacier forefields are the landscape formed by retreating glaciers. As a glacier melts down, bare rock and gravel that
have been covered by the glacier are released. This material is then subjected to weathering and to soil forming
processes. The young soils characterising glacier forefields are generally scarcely vegetated and low in nutrients such as
C, N, P and S. Bedrock properties determine the physico-chemical properties of the corresponding soils such as texture,
pH, nutrient concentrations, heat and humidity retention, water and gas fluxes. Moreover, they are characterized by
strong physical extremes, in particular concerning temperature and water regimes. Such conditions may also vary
locally. Site morphology and slope orientation, for example, may be related to different precipitation and irradiation.
The climate at glacier forefields is generally highly variable: for example, precipitation tends to be more frequent in
spring and in autumn; winters are instead characterized by heavy snowfall, which melts relatively fast in spring. Strong
day-night fluctuations in soil temperatures are also often observable [1].
The colonization of the exposed bedrock by pioneer microorganisms which can well adapt to the low nutrient
conditions and climatic fluctuations is the first step in soil development (Fig. 1). Pioneer microorganisms are involved
in all the major biogeochemical cycles, contribute to mineral weathering and subsequent release of nutrients [2], which
in turn favours the establishment of more complex and efficient microbial communities and plants [3]. Microbial
communities are therefore vital for the initiation and maintenance of nutrient cycling and ecosystem productivity. In
soil, 80-90% of soil function is provided by microbes [4].
Fig. 1. Schematic representation of components (white boxes) and processes (black boxes) the forefield of a retreating glacier. The
white arrows represent possible origins of the pioneer communities (below glacier, above glacier, from the surroundings)
Denitrification qPCR of nirS, nirK, nosZ Glacier forefield [64, 65, 66]Nitrification qPCR on amoA Glacier forefield [64]C-cycleRespiration Soil respiration Glacier forefield [22, 43]Photosynthesis CO2 gas exchange rates Glacier forefield [67]P-cycleP solubilisation Enzymes Glacier forefield [1]S-cycleS0-reduction T-RFLP of asfA Glacier forefield [30]
4. Adaptation of glacier forefield microbial communities to changing environmentalconditions
Environmental factors may all represent a stress if they fluctuate away from the normal range observed in nature [68].The consequences of environmental changes on microbial community structure and activity involve disturbances offunctions and variations in community composition, because organisms which can tolerate and better adapt to the newenvironmental conditions will grow and outcompete other organisms. Cells are able to respond to environmentalchanges by adjusting their physiology and metabolism. Some microbial responses have evolved in relation topredictable environmental changes, such as seasonal or circadian cycles [69]. Unpredictable changes instead involvespecific gene expression which may lead to long-term adaptation.
The type and extent of the responses of microbial communites to disturbances are an index of stability of thecommunity, and can be defined by the concepts of resistance and resilience [70, 71]. Resistance defines the capacity ofa system to maintain functions throughout a disturbance, while resilience has been used to define the time for a systemto return to equilibrium after a disturbance ([72, 73], Fig. 4).
Fig. 4. Schematic representation of the concepts of resistance and resilience. The 3 curves (dotted, dashed and full) representdifferent parameters (eg. biomass, diversity, activity, including natural fluctuations) which diverge after the change of anenvironmental factor (t0) indicating possible responses; In gray, area of normal range; for clarity, only a negative deviation from thenormal range is depicted [74].
Current Research. Technology and Education Topics in Applied Microbiology and Microbial Biotechnology A. Méndez-Vilas (Ed.)
overview of the relationships of microbial community structure and functions under natural physical and chemical
conditions.
Acknowledgements. Research on glacier forefields within the Environmental Microbiology Group, Institute of Biogeochemistry and
Pollutant Dynamics, ETH Zurich has partially been funded within the CCES BigLink project.
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