| 1. |
- Berger, S. A., et al.
(författare)
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Water temperature and mixing depth affect timing and magnitude of events during spring succession of the plankton
- 2007
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Ingår i: Oecologia. ; 150:4, s. 643-654
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Tidskriftsartikel (refereegranskat)abstract
- In many lakes, the most conspicuous seasonal events are the phytoplankton spring bloom and the subsequent clear-water phase, a period of low-phytoplankton biomass that is frequently caused by mesozooplankton (Daphnia) grazing. In Central European lakes, the timing of the clear-water phase is linked to large-scale climatic forcing, with warmer winters being followed by an earlier onset of the clear-water phase. Mild winters may favour an early build-up of Daphnia populations, both directly through increased surface temperatures and indirectly by reducing light limitation and enhancing algal production, all being a consequence of earlier thermal stratification. We conducted a field experiment to disentangle the separate impacts of stratification depth (affecting light supply) and temperature on the magnitude and timing of successional events in the plankton. We followed the dynamics of the phytoplankton spring bloom, the clear-water phase and the spring peak in Daphnia abundance in response to our experimental manipulations. Deeper mixing delayed the timing of all spring seasonal events and reduced the magnitudes of the phytoplankton bloom and the subsequent Daphnia peak. Colder temperatures retarded the timing of the clear-water phase and the subsequent Daphnia peak, whereas the timing of the phytoplankton peak was unrelated to temperature. Most effects of mixing depth (light) and temperature manipulations were independent, effects of mixing depth being more prevalent than effects of temperature. Because mixing depth governs both the light climate and the temperature regime in the mixed surface layer, we propose that climate-driven changes in the timing and depth of water column stratification may have far-reaching consequences for plankton dynamics and should receive increased attention.
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| 2. |
- Striebel, M., et al.
(författare)
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Carbon sequestration and stoichiometry of motile and nonmotile green algae
- 2009
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Ingår i: Limnology and Oceanography. ; 54:5, s. 1746-1752
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Tidskriftsartikel (refereegranskat)abstract
- Actively motile, flagellated phytoplankton taxa often exploit vertical gradients in the availability of light and nutrients. The ability to move actively usually goes along with low investment in structural carbon components and should entail costs in terms of increased energy expenditure. This should be reflected in higher metabolic rates and higher light requirements for growth and, consequently, in lower light-dependent specific production rates, carrying capacities, and carbon-to-phosphorus (C : P) ratios (during phosphorus limitation) of flagellated compared to nonmotile taxa. Laboratory experiments with four flagellated and five nonmotile species of green algae, performed over a light gradient, corroborated these expectations. Parameter fits to short-term production-irradiance measurements suggest that flagellated taxa had higher respiration rates and higher light requirements for growth than nonmotile taxa. Accordingly, both short-term photosynthetic rates and longer-term (14 d) biomass accrual were lower for flagellated than for nonmotile taxa. While most of the variance in algal C : P ratios was explained by species-specific effects, there was also a tendency for algal C : P ratios to be lower in flagellated that in nonmotile taxa. Collectively, these results point at significant costs of motility, which may explain why flagellated taxa are often outcompeted by nonmotile taxa in turbulently mixed environments, where active motility is of little use.
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| 3. |
- Striebel, M., et al.
(författare)
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Spectral Niche Complementarity and Carbon Dynamics in Pelagic Ecosystems
- 2009
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Ingår i: American Naturalist. ; 174:1, s. 141-147
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Tidskriftsartikel (refereegranskat)abstract
- Positive effects of biodiversity on ecosystem function are described from an increasing number of systems, but the underlying mechanisms frequently remain elusive. A truly predictive understanding of biodiversity-ecosystem function relationships requires the a priori identification of traits conferring specific ( and possibly complementary) functions to individual species. Although planktonic organisms are responsible for approximately half of the world's primary production, few studies have reported on the relationship between phytoplankton biodiversity and planktonic primary production. We argue that taxon-specific differential equipment with photosynthetically active pigments provides a biochemical mechanism of resource use complementarity among phototrophic microorganisms, enabling more diverse communities to more completely harvest the light spectrum. In line with this, more diverse phytoplankton communities showed higher pigment diversity, higher biomass-specific light absorbance, and higher rates of primary production and biomass accrual.
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