Samenvatting
Summary
Soil microorganisms are involved in all the major global biogeochemical cycles, but
consequences of ongoing climate changes on these organisms and associated functions are
mostly unknown. Antarctic terrestrial habitats are ideal testing grounds for the impacts of
perturbation on soil microbes, and the ecosystem functions for which they are responsible.
Indeed, the unusually harsh environmental conditions of terrestrial Antarctic habitats result
in ecosystems with simplified trophic structures, where microbial processes are especially
dominant as drivers of soil-borne nutrient cycling. The Antarctic Peninsula is one of the
most rapidly warming regions in the world, yet few studies have addressed the potential
impacts of global warming on soil microbes and associated nutrient-cycling functions
inhabiting these simple and vulnerable environments.
The main objective of this thesis is to assess the effects of global warming on Antarctic
soil-borne microorganisms and associated functions. This objective was pursued via three
complementary experimental approaches:
1. A detailed description of the microbial communities, and their associated functions,
inhabiting Antarctic terrestrial habitats along a latitudinal transect, as a proxy for longterm,
large-scale climatic changes (Chapters 2–5).
2. A study of the short-term responses of soil microorganisms and associated functions to
increasing temperature and altered freeze-thaw cycle frequency in controlled
microcosm experiments (Chapter 6).
3. An assessment of the responses of soil microbial communities and functions in a field
manipulation experiment involving three years of artificial enhancement of soil
temperature warming using open-top chambers at three field locations (Chapter 7).
Such an integrated approach is thought to help overcome methodological, spatial and
temporal limitations and to help discriminate between general and context-dependant
responses of ecosystems to global warming.
Results from the latitudinal gradient studies revealed that the large differences in climatic
conditions at the different sites sampled exerted strong influence on microbial community
structure, diversity, abundance and functions. In addition, vegetation cover was observed to
also exert a strong effect, indicating that indirect effects of global warming through
vegetation expansion may lead to large ecosystem responses. Microcosm studies
highlighted that fungi and bacteria respond differently to increasing temperature and
changes in freeze-thaw cycle frequency. These experiments also showed that several
functional genes involved in the N-cycle were more sensitive to changes in freeze-thaw
cycle frequency than to increases in temperature. Field warming experiments showed that
the short-term responses of soil organisms and associated functions to warming of a few
degrees were highly dependent on local environmental condition. Large responses were
only recorded in moist, nutrient-rich Antarctic environments, while few responses were
observed in nutrient- or water-limited environments and the more temperate soils.
Taken together, the results presented in this thesis suggest that global warming will have
profound effects on Antarctic soil microorganisms and associated functions. The short-term
effects will be highly variable and shaped by local environmental conditions, while in the
longer-term, global warming will strongly affect soil microorganisms and nutrient-cycling
functions, both directly and indirectly.
Soil microorganisms are involved in all the major global biogeochemical cycles, but
consequences of ongoing climate changes on these organisms and associated functions are
mostly unknown. Antarctic terrestrial habitats are ideal testing grounds for the impacts of
perturbation on soil microbes, and the ecosystem functions for which they are responsible.
Indeed, the unusually harsh environmental conditions of terrestrial Antarctic habitats result
in ecosystems with simplified trophic structures, where microbial processes are especially
dominant as drivers of soil-borne nutrient cycling. The Antarctic Peninsula is one of the
most rapidly warming regions in the world, yet few studies have addressed the potential
impacts of global warming on soil microbes and associated nutrient-cycling functions
inhabiting these simple and vulnerable environments.
The main objective of this thesis is to assess the effects of global warming on Antarctic
soil-borne microorganisms and associated functions. This objective was pursued via three
complementary experimental approaches:
1. A detailed description of the microbial communities, and their associated functions,
inhabiting Antarctic terrestrial habitats along a latitudinal transect, as a proxy for longterm,
large-scale climatic changes (Chapters 2–5).
2. A study of the short-term responses of soil microorganisms and associated functions to
increasing temperature and altered freeze-thaw cycle frequency in controlled
microcosm experiments (Chapter 6).
3. An assessment of the responses of soil microbial communities and functions in a field
manipulation experiment involving three years of artificial enhancement of soil
temperature warming using open-top chambers at three field locations (Chapter 7).
Such an integrated approach is thought to help overcome methodological, spatial and
temporal limitations and to help discriminate between general and context-dependant
responses of ecosystems to global warming.
Results from the latitudinal gradient studies revealed that the large differences in climatic
conditions at the different sites sampled exerted strong influence on microbial community
structure, diversity, abundance and functions. In addition, vegetation cover was observed to
also exert a strong effect, indicating that indirect effects of global warming through
vegetation expansion may lead to large ecosystem responses. Microcosm studies
highlighted that fungi and bacteria respond differently to increasing temperature and
changes in freeze-thaw cycle frequency. These experiments also showed that several
functional genes involved in the N-cycle were more sensitive to changes in freeze-thaw
cycle frequency than to increases in temperature. Field warming experiments showed that
the short-term responses of soil organisms and associated functions to warming of a few
degrees were highly dependent on local environmental condition. Large responses were
only recorded in moist, nutrient-rich Antarctic environments, while few responses were
observed in nutrient- or water-limited environments and the more temperate soils.
Taken together, the results presented in this thesis suggest that global warming will have
profound effects on Antarctic soil microorganisms and associated functions. The short-term
effects will be highly variable and shaped by local environmental conditions, while in the
longer-term, global warming will strongly affect soil microorganisms and nutrient-cycling
functions, both directly and indirectly.
| Originele taal-2 | Engels |
|---|---|
| Kwalificatie | Doctor (dr.) |
| Toekennende instantie |
|
| Begeleider(s)/adviseur |
|
| Datum van toekenning | 30 jun. 2008 |
| Plaats van publicatie | Amsterdam |
| Uitgever | |
| Status | Gepubliceerd - 30 jun. 2008 |