| 1. |
- Dinnétz, Patrik, et al.
(författare)
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Population viability analysis of Saxifraga cotyledon, a perennial plant with semelparous rosettes
- 2002
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Ingår i: Plant Ecology. - 1385-0237 .- 1573-5052. ; 159:1, s. 61-71
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Tidskriftsartikel (refereegranskat)abstract
- The aim with this study was to analyse the population dynamics of Saxifraga cotyledon, a rare, long lived herb, with semelparous rosettes. In Sweden, S. cotyledon grows in fragmented habitats at high altitude and is classified as vulnerable according to the IUCN system. From a five year demographical study we estimated population growth rates and extinction risks for one small and one large subpopulation. In the small subpopulation deterministic matrix simulations showed large variation, with two transitions projecting negative and two projecting positive population growth. The large subpopulation also showed large variation, but all yearly transitions projected positive population growth. In both subpopulations survival and growth contributed more than twice as much to population growth rates than did sexual reproduction, vegetative reproduction and the seed bank all taken together. In stochastic simulations the maximum likelihood growth estimator was larger than 1 for both subpopulations. None of the two subpopulations suffer from high extinction rates and although the effect of demographic stochasticity increase extinction risk in small populations it is enough with 70 individuals for a viable population of S. cotyledon. Hence, for the studied population of S. cotyledon, rareness per se is not a good indicator of vulnerability.
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| 2. |
- Björn, Lars Olof, et al.
(författare)
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Is provitamin D a UV-B receptor in plants?
- 2001
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Ingår i: Plant Ecology. - 1573-5052. ; 154:1-2, s. 1-1
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Tidskriftsartikel (refereegranskat)abstract
- An hypothesis is presented that provitamin D (dehydrocholesterol and/or ergosterol) can act as a UV-B receptor in plants and algae. We also propose that the proportions between provitamins D, previtamins D, and vitamins D (D2 and D3), after calibration, can be used to evaluate UV-B exposure of phytoplankton and terrestrial vegetation. This is the final, accepted and revised manuscript of this article. Use alternative location to go to the published article. Requires subscription. The original publication is available at www.springerlink.com .
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| 3. |
- Falkengren-Grerup, Ursula, et al.
(författare)
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Vascular plants as indicators of nitrogen enrichment in soils
- 2004
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Ingår i: Plant Ecology. - 1573-5052. ; 172:1, s. 51-62
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Tidskriftsartikel (refereegranskat)abstract
- The quantification of species along environmental gradients has long been the subject of study regarding natural plant communities and, more recently, ecosystems disturbed by anthropogenic emissions of eutrophying and acidifying substances. We studied 527 sites in southern Swedish deciduous forests divided into two regions, with mean nitrogen depositions of 17 and 9 kg ha(-1) y(-1). The higher deposition in the more exposed region has resulted in higher nitrogen mineralisation and nitrification rates. The objective was to identify nitrogen indicators, which we defined as species with a skewed distribution in relation to the net potential nitrogen mineralisation in the soil. Soil pH was introduced as a co-variable as it may relate to other factors limiting plant growth and survival in these ecosystems. We tested the distribution of the net potential mineralised ammonium (minNH(4)(+)), nitrate (minNO(3)(-)), total inorganic nitrogen (minNH(4)(+)+NO3-) and the ratio of nitrification (percentage of minNH(4)(+)+NO3- as nitrate; %minNO(3)(-)) in 77 herbs. The number of species that showed a skewed distribution differed for the nitrogen variables studied in the following order: %minNO(3)(-) > minNO(3)(-) > minNH(4)(+) much greater than minNH(4)(+)+NO3-. As many as 21 species in region 1 and 17 species in region 2 were selected as indicators for one or several of the nitrogen variables. A fern, five graminoids and seven forbs were found to be indicators of low %minNO(3)(-) and two ferns, two grasses and 13 forbs were found to be indicators of high %minNO(3)(-). We correlated the Ellenberg N indicator values with species with and without skewed distributions, and found that the former group was best related to the N values. As with most indicators, the species identified here are probably best used in combination with other measures to demonstrate the effects of nitrogen deposition on vegetation.
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| 4. |
- Gaberscik, A, et al.
(författare)
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The influence of enhanced UV-B radiation on the spring geophyte Pulmonaria officinalis
- 2001
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Ingår i: Plant Ecology. - 1573-5052. ; 154:1-2, s. 49-56
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Tidskriftsartikel (refereegranskat)abstract
- Pulmonaria officinalis is an understorey spring geophyte, which starts its vegetative period before full foliation of the tree storey. During its early growth phase it is exposed to full solar radiation, therefore the enhanced UV-B radiation could present a threat to this species. An outdoor experiment in which potted plants were exposed to below ambient, ambient, and above ambient (corresponding to 17% ozone reduction) UV-B radiation, was conducted in order to evaluate the radiation effects. The amount of photosynthetic pigments and photochemical efficiency of PSII were not affected, but the amount of UV-B absorbing compounds was lower in plants grown under reduced UV-B. This change was measurable after only fourteen days in reproductive shoots, while in the vegetative shoots, it was not detectable until after three months. The leaves of P. officinalis are variegated and the light green spots became less transparent to PAR under enhanced UV-B. The results reveal that under simulated 17% ozone depletion the harmful effects of UV-B on the measured parameters were negligible. This is the final, accepted and revised manuscript of this article. Use alternative location to go to the published article. Requires subscription. The original publication is available at www.springerlink.com.
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| 5. |
- Moody, Sandra A., et al.
(författare)
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The direct effects of UV-B radiation on Betula pubescens litter decomposing at four European field sites
- 2001
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Ingår i: Plant Ecology. - 1573-5052. ; 154:1-2, s. 27-36
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Tidskriftsartikel (refereegranskat)abstract
- A co-ordinated series of field experiments were conducted to consider the effects of elevated UV-B radiation applied directly to decomposing plant litter. Betula pubescens was decomposed under ambient and elevated UV-B (simulating a 15% ozone depletion) using outdoor irradiation facilities at Adventdalen, Norway (78° N), Abisko, Sweden (68° N), Amsterdam, The Netherlands (52° N,) and Patras, Greece (38° N). There was no significant effect of treatment on mass loss for samples collected after 2, 12 and 14 months decomposition at Amsterdam, or after 4 months decomposition at Adventdalen. Significant reductions in the mass loss of litter decomposing under elevated UV-B compared to ambient were found at the other 2 sites. The only effect of treatment on litter chemistry during decomposition was a significant reduction in the N concentration of material at Abisko and a significant increase in C:N at Patras for litter decomposing under elevated UV-B. Significant differences were found in the structure of the fungal community decomposing litter in Sweden, the only site to be tested. These data, and the few published studies of the response of decomposition to UV-B incident on litter suggest that, in the ecosystems and climates that have been studied, such direct effects are typically confined to the initial stages of decomposition, and are rather small in magnitude.
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