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- Cornelissen, Johannes H C, et al.
(författare)
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Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes
- 2007
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 10:7, s. 619-627
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Tidskriftsartikel (refereegranskat)abstract
- Whether climate change will turn cold biomes from large long-term carbon sinks into sources is hotly debated because of the great potential for ecosystem-mediated feedbacks to global climate. Critical are the direction, magnitude and generality of climate responses of plant litter decomposition. Here, we present the first quantitative analysis of the major climate-change-related drivers of litter decomposition rates in cold northern biomes worldwide.Leaf litters collected from the predominant species in 33 global change manipulation experiments in circum-arctic-alpine ecosystems were incubated simultaneously in two contrasting arctic life zones. We demonstrate that longer-term, large-scale changes to leaf litter decomposition will be driven primarily by both direct warming effects and concomitant shifts in plant growth form composition, with a much smaller role for changes in litter quality within species. Specifically, the ongoing warming-induced expansion of shrubs with recalcitrant leaf litter across cold biomes would constitute a negative feedback to global warming. Depending on the strength of other (previously reported) positive feedbacks of shrub expansion on soil carbon turnover, this may partly counteract direct warming enhancement of litter decomposition.
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| 4. |
- Jägerbrand, Annika K.
(författare)
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Effects of an in situ temperature increase on the short-term growth of arctic-alpine bryophytes
- 2007
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Ingår i: Lindbergia. - : Nordic Bryological Society and the Dutch Bryological and Lichenological Society. - 0105-0761 .- 2001-5909. ; 32:3, s. 82-87
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Tidskriftsartikel (refereegranskat)abstract
- This study examined the short-term growth responses to a temperature increase in situ of three bryophytes species of different genera. Temperatures were enhanced by the use of open-top chambers at Latnjajaure, a subarctic-alpine site in northernmost Sweden. Growth was measured during the growing season of 1995, using the tied-thread method for Aulacomnium turgidum, the cranked-wire method for Sphagnum teres, and the shoot-transplanting method for Tomentypnum nitens. Temperature enhancement significantly increased the growth in length of Sphagnum teres while no significant effects were found for the other two species. One possible reason for this is that Sphagnum teres had more water available, while the other two species could not respond to increased temperature due to constraints of water availability.
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| 5. |
- Jägerbrand, Annika K, 1972-, et al.
(författare)
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Effects of simulated shade on growth, number of branches and biomass in Hylocomium splendens and Racomitrium lanuginosum
- 2005
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Ingår i: Lindbergia. - 0105-0761 .- 2001-5909. ; 30:3, s. 117-124
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Tidskriftsartikel (refereegranskat)abstract
- The effects of simulated shade in terms of reduced light quantity (PPFD) and changed red:far-red ratio (R:FR ratio) on the growth in length, in number of branches and in biomass, were examined in a greenhouse experiment with Hylocomium splendens and Racomitrium lanuginosum, two species from habitats with different light conditions (with H. splendens often in more shaded microsites). Using ten intact moss turfs per species which had been collected on Iceland at 4 m distance between replicate turfs, we tested, whether light quantity affected growth and biomass, whether changes in light quantity and red:far-red ratio affected the number of branches, and whether the two species differed in these responses. Reduced light quantity (i.e. PPFD level) caused a greater length increase, decreased biomass, and biomass:length ratio in both species, but the magnitude of response varied greatly between species. Furthermore, in R. lanuginosum spectral shade (i.e. reduced PPFD and a lower R:FR ratio) generally caused stronger responses than neutral shade, with only a reduction in PPFD. H. splendens (from the shaded habitat) responded less strongly to the shade treatments than R. lanuginosum (from the open habitat) did. In addition to these effects of shading, there were strong effects of the turf of origin in both species, and in many cases the interaction between turf of origin and shading treatment was significant as well. Copyright © Lindbergia 2006.
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| 6. |
- Jägerbrand, Annika K, 1972-, et al.
(författare)
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Phenotypic variation at different spatial scales in relation to environment in two circumpolar bryophyte species
- 2005
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Ingår i: Lindbergia. - : ABE-IPS. - 0105-0761 .- 2001-5909. ; 30:3, s. 125-142
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Tidskriftsartikel (refereegranskat)abstract
- Morphology, physiology and biomass in two widespread bryophyte species, Hylocomium splendens and Racomitrium lanuginosum, were studied to examine the extent to which different species exhibit similar phenotypic variation patterns within and across regions. Analyses of nine morphological variables, chlorophyll content, nitrogen content, C/N ratio and biomass were conducted in samples from five sites in two geographically separated and climatically different regions, Iceland and northern Sweden. Both species exhibited large between-site variation in morphology, physiology and biomass, but within-site variation in morphology was substantially higher in Hylocomium splendens than Racomitrium lanuginosum. Morphological patterns were partly similar, partly different between the species, indicating that the two species respond morphologically to external factors on different scales. The lowest concentrations of chlorophyll and nitrogen were found at the same sites for both species, while the site of highest concentration was not the same. In Hylocomium splendens, chlorophyll content was positively correlated with biomass. Many of the observed relationships between morphological, physiological variables and biomass were species-specific. Our results demonstrate that the two bryophytes exhibit different phenotypic responses to environmental variation. Copyright © Lindbergia 2006.
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| 7. |
- Jägerbrand, Annika K, 1972-, et al.
(författare)
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Plant community responses to 5 years of simulated climate change in meadow and heath ecosystems at a subarctic-alpine site
- 2009
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Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 161:3, s. 601-610
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Tidskriftsartikel (refereegranskat)abstract
- Climate change was simulated by increasing temperature and nutrient availability in an alpine landscape. We conducted a field experiment of BACI-design (before/after control/impact) running for five seasons in two alpine communities (heath and meadow) with the factors temperature (increase of ca. 1.5-3.0°C) and nutrients (5 g N, 5 g P per m 2) in a fully factorial design in northern Swedish Lapland. The response variables were abundances of plant species and functional types. Plant community responses to the experimental perturbations were investigated, and the responses of plant functional types were examined in comparison to responses at the species level. Nutrient addition, exclusively and in combination with enhanced temperature increase, exerted the most pronounced responses at the species-specific and community levels. The main responses to nutrient addition were increases in graminoids and forbs, whereas deciduous shrubs, evergreen shrubs, bryophytes, and lichens decreased. The two plant communities of heath or meadow showed different vegetation responses to the environmental treatments despite the fact that both communities were located on the same subarctic-alpine site. Furthermore, we showed that the abundance of forbs increased in response to the combined treatment of temperature and nutrient addition in the meadow plant community. Within a single-plant functional type, most species responded similarly to the enhanced treatments although there were exceptions, particularly in the moss and lichen functional types. Plant community structure showed BACI responses in that vegetation dominance relationships in the existing plant functional types changed to varying degrees in all plots, including control plots. Betula nana and lichens increased in the temperature-increased enhancements and in control plots in the heath plant community during the treatment period. The increases in control plots were probably a response to the observed warming during the treatment period in the region. © Springer-Verlag 2009.
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