| 1. |
- Alatalo, Juha, 1966-, et al.
(författare)
-
Effect of Altitude on the Sex-Ratio in Populations of Silene Acaulis (Caryophyllaceae) : Effect of Altitude on the Sex-Ratio in Populations of Silene Acaulis (Caryophyllaceae)
- 1995
-
Ingår i: Nordic Journal of Botany. - 0107-055X .- 1756-1051. ; 15:3, s. 251-256
-
Tidskriftsartikel (refereegranskat)abstract
- Predicted increase of female frequencies in gynodioecious Silene acaulis was tested along an altitude gradient in northern Sweden. Average female frequencies for the four sites increased with altitude from 42% to 59% within a short geographical distance. This follows the outcrossing hypothesis, that female frequencies should be positively correlated with selfing rates of hermaphrodites in populations. More adverse environmental conditions should favour gynodioecy in areas where reproduction to a greater part relies on vegetative reproduction or selfing. Further, a significant difference in corolla width was found between females and the larger hermaphrodites, but not between sites. Cushion size and the number of flowers per cushion decreased with altitude.
|
|
| 2. |
- Alatalo, Juha, 1966-
(författare)
-
Gender lability in trioecious Silene acaulis (Caryophyllaceae)
- 1997
-
Ingår i: Nordic Journal of Botany. - : Wiley. - 0107-055X .- 1756-1051. ; 17:2, s. 181-183
-
Tidskriftsartikel (refereegranskat)abstract
- Gender expression of individual cushions of Silene acaulis was shown to vary between years. Fifteen of thirty-nine (= 38%) cushions monitored changed gender expression between 1993 and 1995. Cushions dominated by female flowers were shown to be more stable in gender expression than cushions dominated by male or hermaphrodite flowers.
|
|
| 3. |
- Alatalo, Juha M, 1966-, et al.
(författare)
-
Testing reliability of short-term responses to predict longer-term responses of bryophytes and lichens to environmental change
- 2015
-
Ingår i: Ecological Indicators. - : Elsevier BV. - 1470-160X .- 1872-7034. ; 58, s. 77-85
-
Tidskriftsartikel (refereegranskat)abstract
- Environmental changes are predicted to have severe and rapid impacts on polar and alpine regions. At high latitudes/altitudes, cryptogams such as bryophytes and lichens are of great importance in terms of biomass, carbon/nutrient cycling, cover and ecosystem functioning. This seven-year factorial experiment examined the effects of fertilizing and experimental warming on bryophyte and lichen abundance in an alpine meadow and a heath community in subarctic Sweden. The aim was to determine whether shortterm responses (five years) are good predictors of longer-term responses (seven years). Fertilizing and warming had significant negative effects on total and relative abundance of bryophytes and lichens, with the largest and most rapid decline caused by fertilizing and combined fertilizing and warming. Bryophytes decreased most in the alpine meadow community, which was bryophyte-dominated, and lichens decreased most in the heath community, which was lichen-dominated. This was surprising, as the most diverse group in each community was expected to be most resistant to perturbation. Warming alone had a delayed negative impact. Of the 16 species included in statistical analyses, seven were significantly negatively affected. Overall, the impacts of simulated warming on bryophytes and lichens as a whole and on individual species differed in time and magnitude between treatments and plant communities (meadow and heath). This will likely cause changes in the dominance structures over time. These results underscore the importance of longer-term studies to improve the quality of data used in climate change models, as models based on short-term data are poor predictors of long-term responses of bryophytes and lichens. (C) 2015 Elsevier Ltd. All rights reserved.
|
|
| 4. |
- Alatalo, Juha, 1966-, et al.
(författare)
-
Pollen viability and limitation of seed production in a population of the circumpolar cushion plant, Silene acaulis (Caryophyllaceae)
- 2001
-
Ingår i: Nordic Journal of Botany. - : Wiley. - 0107-055X .- 1756-1051. ; 21:4, s. 365-372
-
Tidskriftsartikel (refereegranskat)abstract
- Pollen viability among genders and limitation of female seed production in a natural trioecious population of the circumpolar cushion plant Silene acaulis was examined. Pollen viability was estimated by an in vitro pollen germination experiment. Both male and hermaphrodite flowers displayed large variation in pollen viability (0-53% in hermaphrodite and 0-54% in male flowers). There was a significant difference between genders in pollen viability: male plants had on average higher pollen viability than hermaphrodite plants. Resource and pollen limitation of seed production was studied by an experiment consisting of three treatments; (I) hand-pollination and removal of all other flowers on the cushion, (II) harid-pollination without removal of other flowers, and (III) open pollination without removal of flowers, Hand-pollination increased seed production, whereas removal of flowers had no effect on seed production. Abortion of pollinated ovules during seed development and seed mass did not differ among treatments. To control for effect of fruit number on seed production, data from naturally pollinated individuals was used. There was a positive correlation between both total number of seeds and fruit number, mean seed number per fruit and fruit number, respectively. These results indicate that seed production of S. acaulis is mainly limited by pollen availability whereas resource competition between fruits is not important as a limiting factor. The possible role of male quality differences between genders and pollen limitation of seed production for maintenance of trioecious reproductive systems is discussed.
|
|
| 5. |
- Alatalo, Juha, 1966-, et al.
(författare)
-
Response to simulated climatic change in an alpine and subarctic pollen-risk strategist, Silene acaulis
- 1997
-
Ingår i: Global Change Biology. - : Wiley. - 1365-2486 .- 1354-1013. ; 3, s. 74-79
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to test if early no overing species respond with increased seed production to climate warming as is predicted for late-flowering seed-risk strategists. Experimental climate warming of about 3 degrees C was applied to two populations of the cushion-forming plant Silene acaulis (L.) Jacq. The experiment was run at one subarctic site and one alpine site for 2 years and 1 year, respectively, using open-top chambers (OTC). The 2-year temperature enhancement at the subarctic site had a marked effect on the flowering phenology. Cushions inside the OTC started flowering substantially earlier than control cushions. Both the male and female phases developed faster in the OTCs, and maturation of capsules occurred earlier. The cushions also responded positively in reproductive terms and produced more mature seeds and had a higher seed/ovule ratio. After 1 year temperature enhancement at the alpine site there was a weak trend for earlier flowering, but there was no significant difference in seed production or seed/ovule ratio.
|
|
| 6. |
- Arft, M, et al.
(författare)
-
Responses of tundra plants to experimental warming : Meta-analysis of the international tundra experiment
- 1999
-
Ingår i: Ecological Monographs. - 0012-9615 .- 1557-7015. ; 69:4, s. 491-511
-
Tidskriftsartikel (refereegranskat)abstract
- The International Tundra Experiment (ITEX) is a collaborative, multisite experiment using a common temperature manipulation to examine variability in species response across climatic and geographic gradients of tundra ecosystems. ITEX was designed specifically to examine variability in arctic and alpine species response to increased temperature. We compiled from one to four years of experimental data from 13 different ITEX sites and used meta-analysis to analyze responses of plant phenology, growth, and reproduction to experimental warming. Results indicate that key phenological events such as leaf bud burst and flowering occurred earlier in warmed plots throughout the study period; however, there was little impact on growth cessation at the end of the season. Quantitative measures of vegetative growth were greatest in warmed plots in the early years of the experiment, whereas reproductive effort and success increased in later years. A shift away from vegetative growth and toward reproductive effort and success in the fourth treatment year suggests a shift from the initial response to a secondary response. The change in vegetative response may be due to depletion of stored plant reserves, whereas the lag in reproductive response may be due to the formation of flower buds one to several seasons prior to flowering. Both vegetative and reproductive responses varied among life-forms; herbaceous forms had stronger and more consistent vegetative growth responses than did woody forms. The greater responsiveness of the herbaceous forms may be attributed to their more flexible morphology and to their relatively greater proportion of stored plant reserves. Finally, warmer, low arctic sites produced the strongest growth responses, but colder sites produced a greater reproductive response. Greater resource investment in vegetative growth may be a conservative strategy in the Low Arctic, where there is more competition for light, nutrients, or water, and there may be little opportunity for successful germination or seedling development. In contrast, in the High Arctic, heavy investment in producing seed under a higher temperature scenario may provide an opportunity for species to colonize patches of unvegetated ground. The observed differential response to warming suggests that the primary forces driving the response vary across climatic zones, functional groups, and through time.
|
|
| 7. |
- Cornelissen, C, et al.
(författare)
-
Global change and arctic ecosystems : is lichen decline a function of increases in vascular plant biomass?
- 2001
-
Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 89:6, s. 984-994
-
Tidskriftsartikel (refereegranskat)abstract
- 1 Macrolichens are important for the functioning and biodiversity of cold northern ecosystems and their reindeer-based cultures and economics. 2 We hypothesized that, in climatically milder parts of the Arctic, where ecosystems have relatively dense plant canopies, climate warming and/or increased nutrient availability leads to decline in macrolichen abundance as a function of increased abundance of vascular plants. In more open high-arctic or arctic-alpine plant communities such a relationship should be absent. To test this, we synthesized cross-continental arctic vegetation data from ecosystem manipulation experiments simulating mostly warming and increased nutrient availability, and compared these with similar data from natural environmental gradients. 3 Regressions between abundance or biomass of macrolichens and vascular plants were consistently negative across the subarctic and mid-arctic experimental studies. Such a pattern did not emerge in the coldest high-arctic or arctic-alpine sites. The slopes of the negative regressions increased across 10 sites as the climate became milder (as indicated by a simple climatic index) or the vegetation denser (greater site above-ground biomass). 4 Seven natural vegetation gradients in the lower-altitude sub- and mid-arctic zone confirmed the patterns seen in the experimental studies, showing consistent negative relationships between abundance of macrolichens and vascular plants. 5 We conclude that the data supported the hypothesis. Macrolichens in climatically milder arctic ecosystems may decline if and where global changes cause vascular plants to increase in abundance. 6 However, a refining of our findings is needed, for instance by integrating other abiotic and biotic effects such as reindeer grazing feedback on the balance between vascular plants and lichens.
|
|
| 8. |
- Cornelissen, Johannes H C, et al.
(författare)
-
Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes
- 2007
-
Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 10:7, s. 619-627
-
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.
|
|
| 9. |
|
|
| 10. |
- Jägerbrand, Annika K, 1972-, et al.
(författare)
-
Plant community responses to 5 years of simulated climate change in meadow and heath ecosystems at a subarctic-alpine site
- 2009
-
Ingår i: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 161:3, s. 601-610
-
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.
|
|
