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  • 101.
    Chang, Christine Chi-Chen
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Slesak, Ireneusz
    Sotnikow, Alexej
    Mullineaux, Philip M.
    Karpinski, Stanislaw
    Karpinska, Barbara
    Functional characterization of the chloroplastic glutathione peroxidases (cpGPXs) in Arabidopsis thaliana: its role in light acclimatory mechanismsManuscript (Other academic)
  • 102.
    Chang, Christine
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Slesak, Ireneusz
    Jorda, Lucia
    Sotnikov, Alexey
    Stockholm University, Faculty of Science, Department of Botany.
    Melzer, Michael
    Miszalski, Zbigniew
    Mullineaux, Philip M.
    Parker, Jane E.
    Karpinska, Barbara
    Karpinski, Stanislaw
    Arabidopsis Chloroplastic Glutathione Peroxidases Play a Role in Cross Talk between Photooxidative Stress and Immune Responses2009In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 150, no 2, p. 670-683Article in journal (Refereed)
    Abstract [en]

    Glutathione peroxidases (GPXs; EC 1.11.1.9) are key enzymes of the antioxidant network in plants and animals. In order to investigate the role of antioxidant systems in plant chloroplasts, we generated Arabidopsis (Arabidopsis thaliana) transgenic lines that are depleted specifically in chloroplastic (cp) forms of GPX1 and GPX7. We show that reduced cpGPX expression, either in transgenic lines with lower total cpGPX expression (GPX1 and GPX7) or in a gpx7 insertion mutant, leads to compromised photooxidative stress tolerance but increased basal resistance to virulent bacteria. Depletion of both GPX1 and GPX7 expression also caused alterations in leaf cell and chloroplast morphology. Leaf tissues were characterized by shorter and more rounded palisade cells, irregular spongy mesophyll cells, and larger intercellular air spaces compared with the wild type. Chloroplasts had larger and more abundant starch grains than in wild-type and gpx7 mutant plants. Constitutively reduced cpGPX expression also led to higher foliar ascorbic acid, glutathione, and salicylic acid levels in plants exposed to higher light intensities. Our results suggest partially overlapping functions of GPX1 and GPX7. The data further point to specific changes in the chloroplast ascorbate-glutathione cycle due to reduced cpGPX expression, initiating reactive oxygen species and salicylic acid pathways that affect leaf development, light acclimation, basal defense, and cell death programs. Thus, cpGPXs regulate cellular photooxidative tolerance and immune responses.

  • 103. Cherian, Sam
    et al.
    Weyens, Niele
    Lindberg, Sylvia
    Stockholm University, Faculty of Science, Department of Botany.
    Vangronsveld, Jaco
    Phytoremediation of Trace element Contaminated Environments and the Potential of Endophytic Bacteria for Improving this Process2012In: Critical reviews in environmental science and technology, ISSN 1064-3389, E-ISSN 1547-6537, Vol. 42, no 21, p. 2215-2260Article, review/survey (Refereed)
    Abstract [en]

    Trace elements (heavy metals and metalloids) are among the most widespread contaminants that pose serious threat to all living organisms. Plant and microbial-assisted remediation holds great promise for in situ remediation of trace element contaminated environments. An extended knowledge of plant processes generally involved in the uptake, translocation, storage and detoxification of contaminants, and plant-microbe interactions were essential in developing improved technologies for environmental clean up. Currently, with the initiation of transgenic technologies, great strides have been made in trace element phytoremediation research. In this review, we provide an overview of the current knowledge of how plants cope with trace elements and discuss the development of transgenic plants with improved trace element remediation capabilities. In addition, this review also addresses the recent progress made towards understanding the plant-microbe interactions, especially of endophytic bacteria (natural and genetically engineered), and their contribution in improving the efficiency and versatility of trace element phytoremediation. 

  • 104. Chow, Fungyi
    et al.
    Pedersen, Marianne
    Stockholm University, Faculty of Science, Department of Botany.
    Oliveira, Mariana C.
    Modulation of nitrate reductase activity by photosynthetic electron transport chain and nitric oxide balance in the red macroalga Gracilaria chilensis (Gracilariales, Rhodophyta)2013In: Journal of Applied Phycology, ISSN 0921-8971, E-ISSN 1573-5176, Vol. 25, no 6, p. 1847-1853Article in journal (Refereed)
    Abstract [en]

    Nitrate reductase (NR), a key enzyme in nitrogen metabolism, has been implicated in the production of nitric oxide (NO) in plants. The effect of photosynthetic electron transport chain inhibitors and NO scavengers or donors on NR activity of Gracilaria chilensis was studied under experimental laboratory conditions. Effective quantum yield (I broken vertical bar (PSII)) and NR activity were significantly diminished by 3-(3,4-dichlorophenyl)-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone, two photosynthetic electron flux inhibitors of photosystem (PS) II and PSI, respectively, but not by diphenyleneiodonium, a NADPH oxidase inhibitor, indicating a direct dependence of NR activity on the PSII and PSI electron flux. Nitrate reductase activity was sensitive to a decrease or increase of NO levels when NO scavenger (2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) and NO donor (sodium nitroprusside) were added. Moreover, the addition of 8Br-cGMP, a secondary signal molecule, stimulated NR activity. These results evidence a modulation of the photosynthetic electron transport chain and NO balance on G. chilensis NR activity. This association could be linked to the crucial tight modulation of nitrogen assimilation and carbon metabolism to guarantee nitrite incorporation into organic compounds and to avoid toxicity by nitrite, reactive oxygen species, or nitric oxide in the cells. Nitric oxide showed to be an important signaling molecule regulating NR activity and cGMP could participate as secondary messenger on this regulation by phosphorylation and desphosphorylation processes.

  • 105. Chung, K.-M
    et al.
    Sano, H
    Stockholm University, Faculty of Science, Department of Botany.
    Finding a missing link in MAP kinase cascade2008In: Plant Signaling & Behavior, Vol. 3, no 606-608Article in journal (Refereed)
  • 106.
    Clergeot, Pierre-Henri
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Schuler, Herwig
    Mortz, Ejvind
    Brus, Maja
    Stockholm University, Faculty of Science, Department of Botany.
    Vintila, Simina
    Stockholm University, Faculty of Science, Department of Botany.
    Ekengren, Sophia
    Stockholm University, Faculty of Science, Department of Botany.
    The Corky Root Rot Pathogen Pyrenochaeta lycopersici Secretes a Proteinaceous Inducer of Cell Death Affecting Host Plants Differentially2012In: Phytopathology, ISSN 0031-949X, E-ISSN 1943-7684, Vol. 102, no 9, p. 878-891Article in journal (Refereed)
    Abstract [en]

    Clergeot, P.-H., Schuler, H., Mortz, E., Brus, M., Vintila, S., and Ekengren, S. 2012. The corky root rot pathogen Pyrenochaeta lycopersici secretes a proteinaceous inducer of cell death affecting host plants differentially. Phytopathology 102:878-891. Pathogenic isolates of Pyrenochaeta lycopersici, the causal agent of corky root rot of tomato, secrete cell death in tomato 1 (CDiT1), a homodimeric protein of 35 kDa inducing cell death after infiltration into the leaf apoplast of tomato. CDiT1 was purified by fast protein liquid chromatography, characterized by mass spectrometry and cDNA cloning. Its activity was confirmed after infiltration of an affinity-purified recombinant fusion of the protein with a C-terminal polyhistidine tag. CDiT1 is highly expressed during tomato root infection compared with axenic culture, and has a putative ortholog in other pathogenic Pleosporales species producing proteinaceous toxins that contribute to virulence. Infiltration of CDiT1 into leaves of other plants susceptible to P lycopersici revealed that the protein affects them differentially. All varieties of cultivated tomato (Solanum lycopersicum) tested were more sensitive to CDiT1 than those of currant tomato (S. pimpinellifolium). Root infection assays showed that varieties of currant tomato are also significantly less prone to intracellular colonization of their root cells by hyphae of P. lycopersici than varieties of cultivated tomato. Therefore, secretion of this novel type of inducer of cell death during penetration of the fungus inside root cells might favor infection of host species that are highly sensitive to this molecule.

  • 107. Collen, Pi Nyvall
    et al.
    Collen, Jonas
    Reis, Marcelo da Silva
    Pedersen, Marianne
    Stockholm University, Faculty of Science, Department of Botany.
    Setubal, Joao C.
    Varani, Alessandro M.
    Colepicolo, Pio
    Oliveira, Mariana C.
    Analysis of expressed sequence tags from the agarophyte Gracilaria tenuistipitata (Rhodophyta)2012In: Journal of Applied Phycology, ISSN 0921-8971, E-ISSN 1573-5176, Vol. 24, no 4, p. 641-647Article in journal (Refereed)
    Abstract [en]

    A total of 3,631 expressed sequence tags (ESTs) were established from two size-selected cDNA libraries made from the tetrasporophytic phase of the agarophytic red alga Gracilaria tenuistipitata. The average sizes of the inserts in the two libraries were 1,600 bp and 600 bp, with an average length of the edited sequences of 850 bp. Clustering gave 2,387 assembled sequences with a redundancy of 53%. Of the ESTs, 65% had significant matches to sequences deposited in public databases, 11% to proteins without known function, and 35% were novel. The most represented ESTs were a Na/K-transporting ATPase, a hedgehog-like protein, a glycine dehydrogenase and an actin. Most of the identified genes were involved in primary metabolism and housekeeping. The largest functional group was thus genes involved in metabolism with 14% of the ESTs; other large functional categories included energy, transcription, and protein synthesis and destination. The codon usage was examined using a subset of the data, and the codon bias was found to be limited with all codon combinations used.

  • 108. Cornelissen, Johannes H. C.
    et al.
    van Bodegom, Peter M.
    Aerts, Rien
    Callaghan, Terry V.
    van Logtestijn, Richard S. P.
    Alatalo, Juha
    Chapin, F. Stuart
    Gerdol, Renato
    Gudmundsson, Jon
    Gwynn-Jones, Dylan
    Hartley, Anne E.
    Hik, David S.
    Hofgaard, Annika
    Jonsdottir, Ingibjorg S.
    Karlsson, Staffan
    Klein, Julia A.
    Laundre, Jim
    Magnusson, Borgthor
    Michelsen, Anders
    Molau, Ulf
    Onipchenko, Vladimir G.
    Quested, Helen M.
    Stockholm University, Faculty of Science, Department of Botany.
    Sandvik, Sylvi M.
    Schmidt, Inger K.
    Shaver, Gus R.
    Solheim, Bjorn
    Soudzilovskaia, Nadejda A.
    Stenstrom, Anna
    Tolvanen, Anne
    Totland, Orjan
    Wada, Naoya
    Welker, Jeffrey M.
    Zhao, Xinquan
    Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes2007In: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 10, no 7, p. 619-627Article in journal (Refereed)
    Abstract [en]

    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.

  • 109. Cornwell, William K.
    et al.
    Cornelissen, Johannes H. C.
    Amatangelo, Kathryn
    Dorrepaal, Ellen
    Eviner, Valerie T.
    Godoy, Oscar
    Hobbie, Sarah E.
    Hoorens, Bart
    Kurokawa, Hiroko
    Perez-Harguindeguy, Natalia
    Quested, Helen M.
    Stockholm University, Faculty of Science, Department of Botany.
    Santiago, Louis S.
    Wardle, David A.
    Wright, Ian J.
    Aerts, Rien
    Allison, Steven D.
    van Bodegom, Peter
    Brovkin, Victor
    Chatain, Alex
    Callaghan, Terry V.
    Diaz, Sandra
    Garnier, Eric
    Gurvich, Diego E.
    Kazakou, Elena
    Klein, Julia A.
    Read, Jenny
    Reich, Peter B.
    Soudzilovskaia, Nadejda A.
    Victoria Vaieretti, M.
    Westoby, Mark
    Plant species traits are the predominant control on litter decomposition rates within biomes worldwide2008In: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 11, no 10, p. 1065-1071Article in journal (Refereed)
    Abstract [en]

    Worldwide decomposition rates depend both on climate and the legacy of plant functional traits as litter quality. To quantify the degree to which functional differentiation among species affects their litter decomposition rates, we brought together leaf trait and litter mass loss data for 818 species from 66 decomposition experiments on six continents. We show that: (i) the magnitude of species-driven differences is much larger than previously thought and greater than climate-driven variation; (ii) the decomposability of a species' litter is consistently correlated with that species' ecological strategy within different ecosystems globally, representing a new connection between whole plant carbon strategy and biogeochemical cycling. This connection between plant strategies and decomposability is crucial for both understanding vegetation-soil feedbacks, and for improving forecasts of the global carbon cycle.

  • 110.
    Cousins, Sara A. O.
    Stockholm University, Faculty of Science, Department of Botany.
    Plant species richness in midfield islets and road verges - the effect of landscape fragmentation2006In: BIOLOGICAL CONSERVATION, ISSN 0006-3207, Vol. 127, no 4, p. 500-509Article in journal (Refereed)
    Abstract [en]

    Small marginal habitats in the rural landscape may play an important role for plant species richness as refugias. Little is known how the surrounding landscape and landscape history influence these patterns. I analysed how plant species richness was affected by isolation, habitat area, past and present land use, and if landscape context matters. Plant species occurrence in two different types of small marginal habitats were analysed, road verges and midfield islets. The study was conducted in two different agricultural landscapes in Sweden; one open modern agricultural landscape and one traditional rural landscape, and the results compared. Present and past land use, and landscape change was analysed using aerial photographs and old maps. There was a large grassland reduction more than 50 years ago in the modern landscape, when there still were quite a lot of grasslands left in the traditional landscape. Area and connectivity were more important for plant incidence in small remnant habitats in the modem landscape, compared to the less fragmented, traditional rural landscape. On the other hand there were more grassland specialists, 23% in the traditional landscape compared to 16%. Species richness became higher on midfield islet if grazing was re-introduced. The legacy of surrounding landscape remains in the species pool for a long time, at least 50 years, even in small grassland fragments. Although small grassland remnants are more sensitive to fragmentation effects compared to larger grasslands, they still encompass a substantial part of the grassland species pool and may be valuable for reconstructing grassland management at a landscape scale.

  • 111.
    Cousins, Sara A. O.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Botany. växtekologi.
    Aggemyr, Elsa
    Stockholm University, Faculty of Science, Department of Botany. växtekologi.
    The influence of field shape, area and surrounding landscape on plant species richness in grazed ex-fields2008In: BIOLOGICAL CONSERVATION, Vol. 141, p. 126-135Article in journal (Refereed)
    Abstract [en]

    Over the past 100 years species-rich semi-natural grasslands have decreased dramatically in Western Europe, where former arable fields (ex-fields) are used instead as pasture. The disappearance of semi-natural grasslands have caused a threat to the biodiversity in agricultural landscapes. Many typical grassland plants are dispersal limited, thus grazed ex-fields can be used to investigate if species spontaneously colonise these new grassland habitats. We examined the relationship between surrounding landscape, field area, shape, distance between edge and centre, and plant species diversity in ex-fields that had been grazed for 15-18 years. The results showed that there were 35% more plant species in fields surrounded by commercial forestry production compared to those surrounded by open agricultural landscape. Area and shape did not influence species richness, although there was increasing number of species in the centre with decreasing distance from the edge. 25% of the species where typical grassland species, and ex-fields surrounded by forest had 91% more grassland species compared to those in the open landscape. It is possible to increase grassland plant occurrences by grazing ex-fields surrounded by forest or other grassland remnant habitats, particularly in landscapes where grazed semi-natural grasslands are scarce.

  • 112.
    Cousins, Sara A. O.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Eriksson, Ove
    Stockholm University, Faculty of Science, Department of Botany.
    After the hotspots are gone: land use history and grassland plant species diversity in a strongly transformed agricultural landscape2008In: Applied Vegetation Science, ISSN 1402-2001, E-ISSN 1654-109X, Vol. 11, no 3, p. 365-374Article in journal (Refereed)
    Abstract [en]

    Question: We asked how landscape configuration and present management influence plant species richness and abundance of habitat specialists in grasslands in a ‘modern’ (much exploited and transformed) agricultural Swedish landscape.

    Location: Selaön, south-eastern Sweden (59°24' N, 17°10' E).

    Methods: Present and past (150 and 50 years ago) landscape pattern was analysed in a 25 km2 area. Species richness was investigated in 63 different grassland patches; grazed and abandoned semi-natural grasslands, and grazed ex-arable fields. Influence of landscape variables; area, past and present grassland connectivity, present management on total species richness, density and abundance of 25 grassland specialists was analysed.

    Results: Semi-natural grasslands (permanent unfertilised pastures or meadows formed by traditional agricultural methods) had declined from 60% 150 years ago to 5% today. There was a significant decline in species richness and density in abandoned semi-natural grasslands. Total species richness was influenced by present management, size and connectivity to present and past grassland pattern. Landscape variables did not influence species density in grazed semi-natural grassland suggesting that maintained grazing management makes grassland patches independent of landscape context. The abundance of 16 grassland specialists was mainly influenced by management and to some extent also by landscape variables.

    Conclusion: Although species richness pattern reflect management and to some extent landscape variables, the response of individual species may be idiosyncratic. The historical signal from past landscapes is weak on present-day species richness in highly transformed, agricultural landscapes. Generalizations of historical legacies on species diversity in grasslands should consider also highly transformed landscapes and not only landscapes with a high amount of diversity hotspots left.

  • 113.
    Cousins, Sara A. O.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Eriksson, Ove
    Stockholm University, Faculty of Science, Department of Botany.
    The influence of management history and habitat on plant species richness in a rural hemiboreal landscape, Sweden2002In: Landscape Ecology, ISSN 0921-2973, E-ISSN 1572-9761, Vol. 17, no 6, p. 517-529Article in journal (Refereed)
    Abstract [en]

    We explored patterns of plant species richness at different spatial scales in 14 habitats in a Swedish rural landscape. Effects of physical conditions, and relationships between species richness and management history reaching back to the 17 (th) century were examined, using old cadastral maps and aerial photographs. The most species-rich habitats were dry open semi- natural grasslands, midfield islets and road verges. Alpha diversity (species richness within sites) was highest in habitats on dry substrates (excluding bedrock with sparse pines) and beta diversity (species richness among sites) was highest in moist to wet habitats. Alpha and beta components of species richness tended to be inversely related among habitats with similar species richness. Management history influenced diversity patterns. Areas managed as grasslands in the 17 th and 18 th century harboured more species than areas outside the villages. We also found significant relationships between species richness and soil type. Silt proved to be the most species- rich topsoil (10- 20 cm) in addition to thin soils top of on green- or limestone bedrock. The variation in species richness due to local relief or form of the site also showed significant relationships, where flat surfaces had the highest number of species. In contrast, no significant relationship was found between species richness and aspect. Our study suggests that present- day diversity patterns are much influenced by management history, and that small habitat, e. g., road verges and midfield islets, are important for maintaining species richness.

  • 114.
    Cousins, Sara A. O.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Eriksson, Åsa
    Stockholm University, Faculty of Science, Department of Botany.
    Franzen, Daniel
    Stockholm University, Faculty of Science, Department of Botany.
    Reconstructing past land use and vegetation patterns using palaeogeographical and archaeological data: A focus on grasslands in Nynas by the Baltic Sea in south-eastern Sweden2002In: Landscape and Urban Planning, ISSN 0169-2046, E-ISSN 1872-6062, Vol. 61, no 1, p. 1-18Article in journal (Refereed)
    Abstract [en]

    Past landscape characteristics were reconstructed in Nynas, south-eastern Sweden, using geographical and archaeological data together with pollen stratigraphy and an existing shore displacement model, with the aim to explore the development of semi-natural grasslands in the area. A 2.3 m peat core was analysed and radiocarbon dated at three levels. The pollen stratigraphy was estimated to start at approximately 3800 C-14 years before present (BP), at the end of Late Neolithic. Human activities are evident, from both archaeological findings and pollen analysis, for more than 4000 years. Grazing is apparent, possibly more intense around 3200 C-14 years BP, 2500-2600 C-14 years BP, 2100-2200 C-14 years BP, and 1300/1400 C-14 years BP to present day. From 1900+/-80 C-14 years BP and onwards cultivation is intensified at the same time as spruce (Picea abies) expands. Maps on land-cover distribution in the late 17th century was used as a model for the utilisation of the landscape during the Iron Age. Land-covers on very thin soils were grazed and sometimes mown within the village boundaries, but they were also used for cultivation in narrow strips where bedrock is adjacent to clays. Till and varved glacial clays would have been used for cultivation. A reasonable estimation is that 10% of the study area could have been used for cultivation 1900 C-14 years BP, compared to 28% in the end of the 17th century. During the last century there has been a shift towards more arable fields and more forestry. There are 10% open or semi-open grassland left today, and 6% wooded grassland, compared with 47% open or semi-open grassland in the 17th century. Little more than half of the open grasslands are managed today, all by grazing. It is argued that encroachment of trees and shrubs on open or semi-open grasslands will not only reduce species richness in the landscape but also threaten parts of our cultural heritage.

  • 115.
    Cousins, Sara A. O.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Stockholm University, Faculty of Science, Department of Botany. växtekologi.
    Lindborg, Regina
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Remnant grassland habitats as source communities for plant diversification in agricultural landscapes2008In: BIOLOGICAL CONSERVATION, Vol. 141, p. 233-240Article in journal (Refereed)
    Abstract [en]

    Lately there has been a shift in Sweden from grazing species-rich semi-natural grasslands towards grazing ex-arable fields in the modern agricultural landscape. These fields normally contain a fraction of the plant species richness compared to semi-natural grasslands. However, small remnant habitats have been suggested as important for plant species diversity and conservation as they may function as refugia for grassland specialists in fragmented and highly modified agricultural landscapes. In this study, we examined whether plant communities on small remnant habitats, i.e. midfield islets, can function as sources for grassland species to disperse out into surrounding grazed ex-fields (former arable fields). We examined species richness and grassland specialists (species favoured by grazing) and their ability to colonize fields after 5 and 11 years of grazing. The fields that had been grazed for a shorter time were fairly species-poor with few grassland specialists. A longer period of grazing had a positive effect on total and small-scale species diversity in both islets and fields. Species composition became more similar with time, and the number of grassland specialists in both habitats increased. We found that grassland specialists dispersed step-wise into the fields, and the number of grassland specialists decreased with distance from the source. Our study suggests that remnant habitats, such as midfield islets, do function as a source community for grassland specialists and enhance diversification of grassland species when grazing is introduced. For long-term conservation of plant species, incorporating small refugia into larger grazing complexes may thus enhance species richness.

  • 116.
    Cousins, Sara A. O.
    et al.
    Stockholm University, Faculty of Science, Department of Botany. Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Växtekologi.
    Ohlson, Helena
    Stockholm University, Faculty of Science, Department of Botany. Växtekologi.
    Eriksson, Ove
    Stockholm University, Faculty of Science, Department of Botany. Växtekologi.
    Effects of historical and present fragmentation on plant species diversity in semi-natural grasslands in Swedish rural landscapes.2007In: Landscape Ecology, ISSN 0921-2973, Vol. 22, no 5, p. 723-730Article in journal (Refereed)
    Abstract [en]

    Habitat loss and fragmentation of natural and semi-natural habitats are considered as major threats to plant species richness. Recently several studies have pinpointed the need to analyse past landscape patterns to understand effects of fragmentation, as the response to landscape change may be slow in many organisms, plants in particular. We compared species richness in continuously grazed and abandoned grasslands in different commonplace rural landscapes in Sweden, and analysed effects of isolation and area in three time-steps (100 and 50 years ago and today). Old cadastral maps and aerial photographs were used to analyse past and present landscape patterns in 25 sites. Two plant diversity measures were investigated; total species richness and species density. During the last 100 years grassland area and connectivity have been reduced by about 90%. Present-day habitat area was positively related to total species richness in both habitats. There was also a relationship to habitat area 50 years ago for continuously grazed grasslands. Only present management was related to species density: continuously grazed grasslands had the highest species density. There were no relationships between grassland connectivity, present or past, and any diversity measure. We conclude that landscape history is not directly important for present-day plant diversity patterns in ordinary landscapes, although past grassland management is a prerequisite for the grassland habitats that can be found there today. It is important that studies are conducted, not only in very diverse landscapes, but also in managed landscapes in order to assess the effects of fragmentation on species.

  • 117.
    Cousins, Sara A. O.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Vanhoenacker, Didrik
    Stockholm University, Faculty of Science, Department of Botany.
    Detection of extinction debt depends on scale and specialisation2011In: Biological Conservation, ISSN 0006-3207, E-ISSN 1873-2917, Vol. 144, no 2, p. 782-787Article in journal (Refereed)
    Abstract [en]

    Many plants can persist in landscapes for a long time after focal habitats have disappeared or become fragmented, which might contribute to an extinction debt. Delayed responses of plant occurrence have recently received great attention, particularly in conservation, although evidence for extinction debts is incongruent. Here we asked if we could detect an extinction debt for plant species after 100 years of fragmentation, depending on regional or local (gamma or alpha respectively) diversity measure used, and if all plant species or only habitat specialists were investigated. Historical and contemporary grassland patterns were analysed in 33 rural landscapes (each 1 km(2) in diameter) in south-eastern Sweden. Results show that managed semi-natural grassland had declined from 39% to 3% in 100 years. Diversity measured at regional scale was best explained by grassland extent 100 years ago, for both all species and grassland specialists. Present-day management, but neither present nor past grassland extent, was important for grassland specialists' occurrence at the local scale, although present-day grassland proportion had a positive influence on species richness at the local scale. We found evidence of an extinction debt at both local and regional scale when all species were included in the analysis, but not for grassland specialist species at the local scale. However, the extinction debt is still to be settled for grassland specialists at the regional scale, and therefore the estimation of extinction debts in fragmented habitats presents one of the greatest challenges for conservation today and in the future.

  • 118. Crane, Peter R.
    et al.
    Schönenberger, JürgStockholm University, Faculty of Science, Department of Botany. Systematik.
    In Search of the Earliest Flowers2008Collection (editor) (Other academic)
  • 119. Crone, Elizabeth E.
    et al.
    Ellis, Martha M.
    Morris, William F.
    Stanley, Amanda
    Bell, Timothy
    Bierzychudek, Paulette
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Kaye, Thomas N.
    Knight, Tiffany M.
    Lesica, Peter
    Oostermeijer, Gerard
    Quintana-Ascencio, Pedro F.
    Ticktin, Tamara
    Valverde, Teresa
    Williams, Jennifer L.
    Doak, Daniel F.
    Ganesan, Rengaian
    Mceachern, Kathyrn
    Thorpe, Andrea S.
    Menges, Eric S.
    Ability of Matrix Models to Explain the Past and Predict the Future of Plant Populations2013In: Conservation Biology, ISSN 0888-8892, E-ISSN 1523-1739, Vol. 27, no 5, p. 968-978Article in journal (Refereed)
    Abstract [en]

    Uncertainty associated with ecological forecasts has long been recognized, but forecast accuracy is rarely quantified. We evaluated how well data on 82 populations of 20 species of plants spanning 3 continents explained and predicted plant population dynamics. We parameterized stage-based matrix models with demographic data from individually marked plants and determined how well these models forecast population sizes observed at least 5 years into the future. Simple demographic models forecasted population dynamics poorly; only 40% of observed population sizes fell within our forecasts' 95% confidence limits. However, these models explained population dynamics during the years in which data were collected; observed changes in population size during the data-collection period were strongly positively correlated with population growth rate. Thus, these models are at least a sound way to quantify population status. Poor forecasts were not associated with the number of individual plants or years of data. We tested whether vital rates were density dependent and found both positive and negative density dependence. However, density dependence was not associated with forecast error. Forecast error was significantly associated with environmental differences between the data collection and forecast periods. To forecast population fates, more detailed models, such as those that project how environments are likely to change and how these changes will affect population dynamics, may be needed. Such detailed models are not always feasible. Thus, it may be wiser to make risk-averse decisions than to expect precise forecasts from models. Habilidad de los Modelos Matriciales para Explicar el Pasado y Predecir el Futuro de las Poblaciones de Plantas Resumen La incertidumbre asociada con el pronostico ecologico ha sido reconocida durante un largo tiempo pero rara vez se cuantifica su seguridad. Evaluamos que tan bien la informacion de 82 poblaciones de 20 especies de plantas a lo largo de 3 continentes explica y predice la dinamica de poblacion de las plantas. Realizamos parametros con modelos matriciales con base en estadios con datos demograficos a partir de plantas marcadas individualmente y determinamos que tan bien estos modelos pronostican el tamano de las poblaciones al menos 5 anos en el futuro. Los modelos demograficos simples pronosticaron pobremente las dinamicas de poblacion; solamente el 40% de las poblaciones observadas cayo dentro de los limites de confianza de 85% de nuestros pronosticos. Estos modelos sin embargo explicaron la dinamica de poblacion a lo largo de los anos en los que se colectaron datos; los cambios observados en el tamano de la poblacion durante el periodo de colecta de datos estuvieron positivamente correlacionados con la tasa de crecimiento de la poblacion. Asi, estos modelos son por lo menos una manera segura de cuantificar el estado de la poblacion. Los pronosticos debiles no estuvieron asociados con el numero de plantas individuales o con los anos de datos. Probamos si las tasas vitales dependian de la densidad y encontramos que existe dependencia hacia la densidad tanto positiva como negativa, sin embargo la dependencia de densidad no se asocio con el error de pronostico. El error de pronostico estuvo significativamente asociado con diferencias ambientales entre la recoleccion de datos y los periodos de pronostico. Para predecir el destino de las poblaciones se necesitan modelos mas detallados, como aquellos que proyectan los cambios probables en el ambiente y como estos cambios afectaran a la dinamica de las poblaciones. Tales modelos tan detallados no siempre son factibles. Por ello puede ser mejor tomar decisiones aversas a riesgos que esperar pronosticos precisos de los modelos.

  • 120. Crone, Elizabeth E.
    et al.
    Menges, Eric S.
    Ellis, Martha M.
    Bell, Timothy
    Bierzychudek, Paulette
    Ehrlen, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Kaye, Thomas N.
    Knight, Tiffany M.
    Lesica, Peter
    Morris, William F.
    Oostermeijer, Gerard
    Quintana-Ascencio, Pedro F.
    Stanley, Amanda
    Ticktin, Tamara
    Valverde, Teresa
    Williams, Jennifer L.
    How do plant ecologists use matrix population models?2011In: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 14, no 1, p. 1-8Article in journal (Refereed)
    Abstract [en]

    P>Matrix projection models are among the most widely used tools in plant ecology. However, the way in which plant ecologists use and interpret these models differs from the way in which they are presented in the broader academic literature. In contrast to calls from earlier reviews, most studies of plant populations are based on < 5 matrices and present simple metrics such as deterministic population growth rates. However, plant ecologists also cautioned against literal interpretation of model predictions. Although academic studies have emphasized testing quantitative model predictions, such forecasts are not the way in which plant ecologists find matrix models to be most useful. Improving forecasting ability would necessitate increased model complexity and longer studies. Therefore, in addition to longer term studies with better links to environmental drivers, priorities for research include critically evaluating relative/comparative uses of matrix models and asking how we can use many short-term studies to understand long-term population dynamics.

  • 121.
    Dahlberg, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Range margins and refugia2013Report (Other academic)
    Abstract [en]

    Species ranges are restricted in distribution by physical barriers, dispersal ability, abiotic factors such as climate and interspecific interactions. The responses of a species to environmental conditions and biotic factors determine its abundance, distribution and range limits. There are four possible responses for populations facing global climate change. They can acclimate, adapt, shift their ranges or go extinct. During unfavorable conditions populations may shift their ranges and survive in refugia with favorable environmental features. Thereafter they might be able to return to their former distribution when the conditions get favorable again. The term refugium has been used for large scale refugia such as interglacial and glacial refugia (macrorefugia), and for small scale refugia such as microrefugia. The existence of microrefugia is promoted by decoupling of the local climate from the regional climate because this buffers against climate change. Such decoupling is most likely to occur in heterogeneous landscapes. At a range shift, new microrefugia may arise at the eroding edge, while macrorefugia may form from a contracting main (continuous) range.

  • 122.
    Dahlgren, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Ehrlen, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Incorporating environmental change over succession in an integral projection model of population dynamics of a forest herb2011In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 120, no 8, p. 1183-1190Article in journal (Refereed)
    Abstract [en]

    Despite seemingly obvious effects of environmental drivers, mechanisms behind long-term changes in plant population sizes over time are often poorly known. We investigated how soil potassium concentration and seed predation are likely to change over time as a result of succession from deciduous forest to spruce forest, and how this affects population trajectories of Actaea spicata. Observations and addition experiments showed that high soil potassium concentration increased individual growth rates. Among-site comparisons showed that soil potassium concentration was lower where proportion spruce was higher. Incorporation of a gradual increase in spruce over time in an integral projection model where individual growth depended on potassium suggested a net decrease in A. spicata population sizes over forest succession. This result suggests that small changes in factors with small effects on individual performance can influence patterns of species occupancy along successional gradients. We incorporated also density independent and density dependent effects of pre-dispersal seed predation over succession into the same model. Seed predation influenced the tree composition at which A. spicata population growth was positive. However, significant effects of A. spicata population size on seed predation intensity did not translate into important feedback effects on population growth trajectories over succession. Our results illustrate how demographic models can be used to gain understanding of the mechanisms behind effects of environmental change on species abundances and distributions by the simultaneous inclusion of changing abiotic and biotic factors.

  • 123.
    Dahlgren, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Linking environmental variation to population dynamics of a forest herb2009In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 97, no 4, p. 666-674Article in journal (Refereed)
    Abstract [en]

    . Although necessary for understanding and predicting population dynamics, abiotic and biotic interactions have only rarely been coupled to demography and population dynamics.

    2. We estimated effects of 11 environmental factors on survival, growth and fertility of the perennial herb Actaea spicata and incorporated significant factors into integral projection models to assess their effect on population dynamics.

    3. Statistical models suggested that high soil potassium concentration increased individual growth and that seed predation and, to a lesser extent, canopy cover reduced seed production.

    4. Demographic models showed that both soil potassium concentration and pre-dispersal seed predation could reverse population growth from positive to negative. The observed range of soil potassium concentration corresponded to growth rates (lambda) between 0.96 and 1.07, at mean observed seed predation intensity. At observed mean potassium concentration, growth rate ranged from 0.99 to 1.02 over observed seed predation intensities.

    5. Sensitivity of population growth rate to different vital rates strongly influenced the relative effects of the two factors. Elasticity analysis suggested that proportional changes in soil potassium concentration result in seven times larger effects on population growth rate than changes in seed predation.

    6. Synthesis. We conclude that relatively weak associations between environmental factors and vital rates can have substantial long-term effects on population growth. Approaches based on detailed demographic models, that simultaneously assess abiotic and biotic effects on population growth rate, constitute important tools for establishing the links between the environment and dynamics of populations and communities.

  • 124.
    Dahlgren, Johan P.
    Stockholm University, Faculty of Science, Department of Botany.
    Alternative regression methods are not considered in Murtaugh (2009) or by ecologists in general2010In: Ecology Letters, ISSN 1461-023X, E-ISSN 1461-0248, Vol. 13, no 5, p. E7-E9Article in journal (Refereed)
    Abstract [en]

    Murtaugh (2009) recently illustrated that all subsets variable selection is very similar to stepwise regression. This, however, does not necessarily mean both methods are useful. On the contrary, the same problems with overfitting should apply. Ecologists should, if model building is indeed necessary, consider more reliable regression methods now available

  • 125.
    Dahlgren, Johan P.
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Garcia, Maria B.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Nonlinear relationships between vital rates and state variables in demographic models2011In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 92, no 5, p. 1181-1187Article in journal (Refereed)
    Abstract [en]

    To accurately estimate population dynamics and viability, structured population models account for among-individual differences in demographic parameters that are related to individual state. In the widely used matrix models, such differences are incorporated in terms of discrete state categories, whereas integral projection models (IPMs) use continuous state variables to avoid artificial classes. In IPMs, and sometimes also in matrix models, parameterization is based on regressions that do not always model nonlinear relationships between demographic parameters and state variables. We stress the importance of testing for nonlinearity and propose using restricted cubic splines in order to allow for a wide variety of relationships in regressions and demographic models. For the plant Borderea pyrenaica, we found that vital rate relationships with size and age were nonlinear and that the parameterization method had large effects on predicted population growth rates, lambda (linear IPM, 0.95; nonlinear IPMs, 1.00; matrix model, 0.96). Our results suggest that restricted cubic spline models are more reliable than linear or polynomial models. Because even weak nonlinearity in relationships between vital rates and state variables can have large effects on model predictions, we suggest that restricted cubic regression splines should be considered for parameterizing models of population dynamics whenever linearity cannot be assumed.

  • 126.
    Dahlgren, Johan Petter
    Stockholm University, Faculty of Science, Department of Botany.
    Linking plant population dynamics to the local environment and forest succession2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Linking environmental variation to population dynamics is necessary to understand and predict how the environment influences species abundances and distributions. I used demographic, environmental and trait data of forest herbs to study effects of spatial variation in environmental factors on populations as well as environmental change in terms of effects of forest succession on field layer plants. The results show that abundances of field layer species during forest succession are correlated with their functional traits; species with high specific leaf area increased more in abundance. I also found that soil nutrients affect vegetative and flowering phenology of the forest herb Actaea spicata. The effect of nutrients shows that a wider range of environmental factors than usually assumed can influence plant phenology. Moreover, local environmental factors affected also the demography of A. spicata through effects on vital rates. An abiotic factor, soil potassium affecting individual growth rate, was more important for population growth rate than seed predation, the most conspicuous biotic interaction in this system. Density independent changes in soil potassium during forest succession, and to a lesser extent plant population size dependent seed predation, were predicted to alter population growth rate, and thereby the abundance, of A. spicata over time. Because these environmental factors had effects on population projections, they can potentially influence the occupancy pattern of this species along successional gradients. I conclude that including deterministic, as opposed to stochastic, environmental change in demographic models enables assessments of the effects of processes such as succession, altered land-use, and climate change on population dynamics. Models explicitly incorporating environmental factors are useful for studying population dynamics in a realistic context, and to guide management of threatened species in changing environments.

  • 127.
    Dahlgren, Johan Petter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Ehrlén, Johan
    A demographic model of a forest herb in a changing environmentManuscript (Other academic)
  • 128.
    Dahlgren, Johan Petter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Ehrlén, Johan
    Linking environmental variation to population dynamics of a forest herbManuscript (Other academic)
  • 129.
    Dahlgren, Johan Petter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Eriksson, Ove
    Bolmgren, Kjell
    Strindell, Magnus
    Ehrlén, Johan
    Specific leaf area as a superior predictor of changes in field layer abundance during forest succession2006In: Journal of Vegetation Science, ISSN 1100-9233, Vol. 17, no 5, p. 577–582-Article in journal (Refereed)
  • 130.
    Dahlgren, Johan Petter
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    von Zeipel, Hugo
    Ehrlén, Johan
    Variation in vegetative and flowering phenology in a forest herb caused by environmental heterogeneity2007In: American Journal of Botany, ISSN 0002-9122, Vol. 94, no 9, p. 1570–1576-Article in journal (Refereed)
  • 131.
    Dahlgren, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    von Zeipel, Hugo
    Stockholm University, Faculty of Science, Department of Botany.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany. växtekologi.
    Variation in vegetative and flowering phenology in a forest herb caused by environmental heterogeneity2007In: AMERICAN JOURNAL OF BOTANY, Vol. 94, no 9, p. 1570-1576Article in journal (Refereed)
  • 132. Dahlgren, Jonas
    et al.
    Oksanen, Lauri
    Oksanen, Tarja
    Olofsson, Johan
    Hambäck, Peter A.
    Stockholm University, Faculty of Science, Department of Botany.
    Lindgren, Åsa
    Stockholm University, Faculty of Science, Department of Botany.
    Plant defences to no avail?: Responses of plants of varying edibility to food web manipulations in a low arctic scrubland2009In: Evolutionary Ecology Research, ISSN 1522-0613, E-ISSN 1937-3791, Vol. 11, no 8, p. 1189-1203Article in journal (Refereed)
    Abstract [en]

    Background: According to the Green World Hypothesis of Hairston, Smith, and Slobodkin, all plants are edible for some herbivores. Hence, the copious abundance of plant biomass, typical for terrestrial ecosystems, depends on the collective regulatory action of predators on the herbivore guild. According to the counterarguments of Polis and Strong, the defensive traits of terrestrial plants attenuate terrestrial trophic cascades to species-specific trickles, so elimination of predators might lead to increased abundance of inedible plants but will not influence community-level plant biomass. Question: Does the elimination of predators from a low arctic scrubland, with high-quality forage plants and poorly edible evergreen ericoids, lead to a reduction of community-level plant biomass or to an increased abundance of well-defended evergreen ericoids? Methods: In 1991, we introduced grey-sided voles (Myodes rufocanus) to islands, initially harbouring dense scrubland vegetation, and established permanent plots there. In 2000, we transplanted vegetation blocks from a large three-trophic-level island with voles and predators, to two-trophic-level islands with introduced voles but without resident predators, and also to vole-free one-trophic-level islands, and back to the three-trophic-level island. Vole densities were monitored by semi-annual live trapping. Vegetation was monitored by the point-frequency method. Results: In the absence of predators, vole densities increased 3.7-fold and the community-level plant biomass was decimated. The least palatable plant group, evergreen ericoids, suffered especially heavily, whereas palatable herbaceous plants increased in abundance. However, all three functional plant groups responded positively to the elimination of grey-sided voles. Conclusions: Our results corroborate the Green World Hypothesis, indicating that in the absence of predators, plant defences do not prevent runaway consumption of the vegetation. The fate of plants in predator-free systems with browsing vertebrates depends primarily on the accessibility of each plant during the limiting season. Evergreen ericoids then form the most sensitive functional group.

  • 133. Dahlgren, Jonas
    et al.
    Oksanen, Lauri
    Oksanen, Tarja
    Olofsson, Johan
    Hambäck, Peter
    Stockholm University, Faculty of Science, Department of Botany.
    Lindgren, Åsa
    Stockholm University, Faculty of Science, Department of Botany.
    Plant defenses to no avail? responses of plants with varying edibility to food web manipulations in a low arctic scrubland2009In: Evolutionary Ecology Research, ISSN 1522-0613, E-ISSN 1937-3791, Vol. 11, p. 1189-1203Article in journal (Refereed)
    Abstract [en]

    Background: According to the Green World Hypothesis of Hairston, Smith, and Slobodkin, all plants are edible for some herbivores. Hence, the copious abundance of plant biomass, typical for terrestrial ecosystems, depends on the collective regulatory action of predators on the herbivore guild. According to the counterarguments of Polis and Strong, the defensive traits of terrestrial plants attenuate terrestrial trophic cascades to species-specific trickles, so elimination of predators might lead to increased abundance of inedible plants but will not influence community-level plant biomass.

    Question: Does the elimination of predators from a low arctic scrubland, with high-quality forage plants and poorly edible evergreen ericoids, lead to a reduction of community-level plant biomass or to an increased abundance of well-defended evergreen ericoids?

    Methods: In 1991, we introduced grey-sided voles (Myodes rufocanus) to islands, initially harbouring dense scrubland vegetation, and established permanent plots there. In 2000, we transplanted vegetation blocks from a large three-trophic-level island with voles and predators, to two-trophic-level islands with introduced voles but without resident predators, and also to vole-free one-trophic-level islands, and back to the three-trophic-level island. Vole densities were monitored by semi-annual live trapping. Vegetation was monitored by the point-frequency method.

    Results: In the absence of predators, vole densities increased 3.7-fold and the communitylevel plant biomass was decimated. The least palatable plant group, evergreen ericoids, suffered especially heavily, whereas palatable herbaceous plants increased in abundance. However, all three functional plant groups responded positively to the elimination of grey-sided voles.

    Conclusions: Our results corroborate Green World Hypothesis, indicating that in the absence of predators, plant defences do not prevent runaway consumption of the vegetation. The fate of plants in predator-free systems with browsing vertebrates depends primarily on the accessibility of each plant during the limiting season. Evergreen ericoids then form the most sensitive functional group.

  • 134.
    Dahlkild, Åsa
    Stockholm University, Faculty of Science, Department of Botany.
    A comparative study of lichen species richness in lanes and wooded-meadowsManuscript (Other academic)
  • 135.
    Dahlkild, Åsa
    Stockholm University, Faculty of Science, Department of Botany.
    Phylogenetic and ecological studies in lichenology: including studies of both mycobiont and photobiont2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this thesis different aspects in lichens are investigated, namely, the phylogeny of mycobiont and photobiont, and ecology in the form of species richness of certain habitats of the Uppland province, Sweden.

    Analyses of ITS sequences of the lichenized fungi genus Roccella (Roccellaceae) provide an intrageneric topology of the genus with emphasis on the European, Mediterranean and Macaronesian species. One species, Roccella elisabethae Tehler, is described and a key to the Macaronesian and European species is provided. Sequences from five Roccella species are new. One significant result is that the Macaronesian species constitute a monophyletic group.

    Newly designed algal-specific primers were used to amplify the ribosomal ITS region from 25 photobiont specimens from five lichenized fungal species of the family Physciaceae (Lecanorales). Trebouxia impressa was present in all mycobionts except Anaptychia ciliaris, which instead was associated with Trebouxia arboricola. A phylogeny for the photobiont, T. impressa, was compared to a phylogeny of the corresponding mycobionts. The general similarity of the mycobiont and photobiont trees may indicate a coevolutionary history.

    The ribosomal SSU region and the rbcL gene were sequenced from total DNA extracts from thalli of 8 species of Siphula (Icmadophilaceae) and 6 species of Parasiphula (Coccotremataceae). All specimens were found to have Elliptochloris bilobata in a wider sense as photobiont, indicating independent accession of photobionts for the two mycobiont genera.

    The epiphytic lichen flora on Fraxinus exelcior and Acer platanoides in lanes and two types of wooded meadows were investigated in Uppland, Sweden. Altogether 129 lichen species were found, five of which are listed in the Swedish Red List of threatened species. The species richness was affected by substrate, habitat, and distance to dust source. Lanes had the highest species richness, and Fraxinus excelsior had higher species richness than Acer platanoides.

  • 136.
    Dahlkild, Åsa
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Kantvilas, Gintaras
    Grube, Martin
    The identity and relationship of the photobionts associated with the strictly sterile genera Siphula (Icmadophilaceae) and Parasiphula (Coccotremataceae) (Lichenized Ascomycetes)Manuscript (Other academic)
  • 137.
    Dahlkild, Åsa
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Källersjö, Mari
    Lohtander, Katileena
    Tehler, Anders
    Photobiont diversity in Physciaceae (Lecanorales)2001In: The Bryologist, ISSN 0007-2745, Vol. 104, p. 427-536Article in journal (Refereed)
  • 138. Dahlström, Anna
    et al.
    Cousins, Sara A. O.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Eriksson, Ove
    Stockholm University, Faculty of Science, Department of Botany.
    The History (1620-2003) of Land Use, People and Livestock, and the Relationship to Present Plant Species Diversity in a Rural Landscape in Sweden2006In: Environment and History, ISSN 0967-3407, E-ISSN 1752-7023, Vol. 12, p. 191-212Article in journal (Refereed)
    Abstract [en]

    The traditional agriculture in Europe favoured numerous plant and animal species that are presently declining. Integrated studies based on various sources are needed in order to unravel the complex relationships between changing landscapes and biological diversity. The objectives of this study were to describe changes in land use during c. 350 years in a Swedish agricultural landscape in relation to changes in human population and livestock, and to analyse relationships between historical land use and present-day plant species diversity. There were only minor long-term changes in land use, population and livestock between 1640 and 1854 in the two studied hamlets, but detailed data 1620-41 showed a large short-term fluctuation in livestock numbers. After 1854 larger changes took place. Grasslands were cultivated and livestock composition changed. After 1932, livestock number decreased and most of the former grazed outland (areas located outside the fenced infields) turned into forest by natural succession. 7 per cent of the study area is still grazed semi-natural grassland. The highest plant species richness is today found on semi-natural grassland with a long continuity of grazing. The distribution of five target species suggests that previous land use still has an important effect today. The majority of their occurrences are remnant populations located in previous outland pastures which are today forests.

  • 139. Davis, Aaron P.
    et al.
    Razafimandimbison, Sylvain G.
    Stockholm University, Faculty of Science, Department of Botany.
    Three species of Madagascan Plectronia transferred to Peponidium (Vanguerieae, Rubiaceae)2010In: PHYTOTAXA, ISSN 1179-3155, Vol. 10, p. 46-48Article in journal (Refereed)
    Abstract [en]

    Three new combinations are made in the genus Peponidium: P. boivinianum, P. densiflorum and P. micranthum. A lectotype is designated for Plectronia boiviniana.

  • 140. Davis, Aaron
    et al.
    Razafimandimbison, Sylvain G.
    Stockholm University, Faculty of Science, Department of Botany. Stockholm University, Faculty of Science, The Bergius Botanical Garden Museum.
    Andriambololonera, Sylvie
    Nomenclatural changes in the genus Bremeria (Rubiaceae)2011In: Blumea - Journal of plant taxonomy and plant geography, ISSN 0006-5196, E-ISSN 2212-1676, Vol. 56, no 1, p. 4-5Article in journal (Refereed)
    Abstract [en]

    Five new combinations are made in the genus Bremeria: B. arachnocarpa, B. eriantha, B. scabrella, B. landia var. holosericea, and B. landia var. stadmanii. Bremeria gerrardii is conspecific with Gaertnera phanerophlebia, and thus excluded from Bremeria. Lectotypes are designated for Mussaenda erectiloba var. scabrella, M. stadmanii, and M. trichophlebia.

  • 141. De Block, Petra
    et al.
    Razafimandimbison, Sylvain G.
    Stockholm University, Faculty of Science, Department of Botany. Stockholm University, Faculty of Science, The Bergius Botanical Garden Museum.
    Janssens, Steven
    Ochoterena, Helga
    Robbrecht, Elmar
    Bremer, Birgitta
    Stockholm University, Faculty of Science, Department of Botany. Stockholm University, Faculty of Science, The Bergius Botanical Garden Museum.
    Molecular phylogenetics and generic assessment in the tribe Pavetteae (Rubiaceae)2015In: Taxon, ISSN 0040-0262, E-ISSN 1996-8175, Vol. 64, no 1, p. 79-95Article in journal (Refereed)
    Abstract [en]

    This is the first phylogenetic study focused on the Pavetteae, one of the most species-rich and morphologically diverse tribes within the coffee family (Rubiaceae). Fifteen of the 17 currently recognized genera, represented by 85 taxa, were sequenced for rps16, trnT-F and ITS and analysed using Bayesian inference and maximum likelihood methods. The monophyly of the Pavetteae is confirmed. Four major lineages are identified, but their phylogenetic relationships are not fully resolved. The continental African genera Rutidea, Nichallea and Tennantia, the Madagascan genera Homollea and Robbrechtia, and the paleotropical genus Pavetta are monophyletic. Other genera are paraphyletic in their current circumscriptions and the following changes are made: Homolliella is placed in synonymy with Paracephaelis, and Coleactina and Dictyandra with Leptactina, resulting in four new combinations. The large paleotropical genus Tarenna is shown not to be monophyletic. In the future, the name Tarenna should not be used for continental African species. Most of these could be transferred to the hitherto monospecific genus Cladoceras, but other species might constitute altogether new genera. The relationship between the monophyletic Asian-Pacific and Madagascan Tarenna species remains unclear. The phylogeny of the Madagascan genera of the Pavetteae is largely unresolved and the largest Madagascar-centred genus Coptosperma was not recovered as monophyletic. The low resolution for the Madagascan taxa can be considered as an indication of rapid radiation. Further molecular and morphological studies are necessary to clarify the phylogeny of the Pavetteae, especially regarding the African Tarenna species and the Madagascan genera of the tribe.

  • 142. De Frenne, P
    et al.
    Graae, B J
    Kolb, A
    Brunet, J
    Chabrerie, O
    Cousins, S A O
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Decocq, G
    Dhondt, R
    Diekmann, M
    Eriksson, Ove
    Stockholm University, Faculty of Science, Department of Botany.
    Heinken, T
    Hermy, M
    Jögar, U
    Saguez, R
    Shevtsova, A
    Stanton, S
    Zindel, R
    Zobel, M
    Verheyen, K
    Significant effects of temperature on the reproductive output of the forest herb Anemone nemorosa L.2010In: Forest Ecology and Management, ISSN 0378-1127, E-ISSN 1872-7042, Vol. 259, no 4, p. 809-817Article in journal (Refereed)
    Abstract [en]

    Climate warming is already influencing plant migration in different parts of the world.Numerous modelshave been developed to forecast future plant distributions. Few studies, however, have investigated thepotential effect of warming on the reproductive output of plants. Understorey forest herbs in particular,have received little attention in the debate on climate change impacts.This study focuses on the effect of temperature on sexual reproductive output (number of seeds, seedmass, germination percentage and seedling mass) of Anemone nemorosa L., a model species for slowcolonizing herbaceous forest plants. We sampled seeds of A. nemorosa in populations along a 2400 kmlatitudinal gradient from northern France to northern Sweden during three growing seasons (2005, 2006and 2008). This study design allowed us to isolate the effects of accumulated temperature (GrowingDegree Hours; GDH) from latitude and the local abiotic and biotic environment. Germination and seedsowing trials were performed in incubators, a greenhouse and under field conditions in a forest. Finally,we disentangled correlations between the different reproductive traits of A. nemorosa along thelatitudinal gradient.We found a clear positive relationship between accumulated temperature and seed and seedlingtraits: reproductive output of A. nemorosa improved with increasing GDH along the latitudinal gradient.Seedmass and seedling mass, for instance, increased by 9.7% and 10.4%, respectively, for every 1000 8C hincrease in GDH.Wealso derived strong correlations between several seed and seedling traits both underfield conditions and in incubators. Our results indicate that seed mass, incubator-based germinationpercentage (Germ%Inc) and the output of germinable seeds (product of number of seeds and Germ%Incdivided by 100) from plants grown along a latitudinal gradient (i.e. at different temperature regimes)provide valuable proxies to parameterize key population processes in models.We conclude that (1) climate warming may have a pronounced positive impact on sexualreproduction of A. nemorosa and (2) climate models forecasting plant distributions would benefit fromincluding the temperature sensitivity of key seed traits and population processes.

  • 143. De Frenne, P
    et al.
    Kolb, A
    Verheyen, K
    Brunet, J
    Chabrerie, O
    Decocq, G
    Diekmann, M
    Eriksson, Ove
    Stockholm University, Faculty of Science, Department of Botany.
    Heinken, T
    Hermy, M
    Jögar, U
    Stanton, S
    Quataert, P
    Zindel, R
    Zobel, M
    Graae, B J
    Unraveling the effects of temperature, latitude and local environment on the reproduction of forest herbs.2009In: Global Ecology and Biogeography, ISSN 1466-822X, E-ISSN 1466-8238, Vol. 18, p. 641-651Article in journal (Refereed)
  • 144.
    De La Torre-Castro, Maricela
    et al.
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Eklöf, Johan
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Rönnbäck, Patrik
    Stockholm University, Faculty of Science, Department of Systems Ecology.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Botany.
    Seagrass importance in food provisioning services: fish stomach content as a link between seagrass meadows and local fisheries2008In: Western Indian Ocean journal of marine science, ISSN 0856-860X, Vol. 7, no 1, p. 95-110Article in journal (Refereed)
    Abstract [en]

    The links between ecosystem processes and functions and ecosystem services (i.e. the humanbenefits from those) are elusive. In this paper, the food provisioning service of seagrass meadows isoperationalized through the study of the stomach contents of 13 important commercial fish species inChwaka Bay, Zanzibar. Using local fishers’ knowledge on bait, scientific knowledge about the structureof the meadows (associated flora and fauna), stomach content analysis and multivariate statistics, the foodprovisioning service associated with seagrasses and its importance for fish (as important diet component)and for humans (in small-scale artisanal fisheries) are described. The study presents the food items for 13commercial fish species identified at the lowest possible taxonomical level and compares with previousliterature findings. In addition, differences in stomach contents of Siganus sutor and Leptoscarus vaigiensiscaught with both drag-nets and dema basket traps are investigated in order to explore bait presence andindirectly evaluate fishers’ knowledge on bait preference. The results show that most of the items consumedby commercial fishes are associated with seagrass beds and that there are clear indicators that the baittraditionally used seems to be effective. The paper elaborates on the consideration of seagrass ecosystemsin a holistic perspective, the difficulties in valuation of ecosystem services and finally the crucial importanceof these aspects for human well-being and sustainability in coastal communities of the Western IndianOcean.

  • 145. Degerholm, Jenny
    et al.
    Gundersen, Kjell
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    Söderbäck, Erik
    Seasonal significance of N2 fixation in coastal and offshore waters of the northwestern Baltic Sea2008In: Marine Ecology Progress Series, ISSN 0171-8630, Vol. 360, p. 73-84Article in journal (Refereed)
    Abstract [en]

    Annual rates of N2 fixation were measured over 3 yr (1998–2000) at an open water station (BY31) and 2 coastal stations (H4 and X1) in the Baltic Sea. This is the first report on depth-integrated rates of N2 fixation from more than one complete growth season in the Baltic Sea. Annual estimates of N2 fixation ranged from 56000 to 125000 t N in the Baltic Proper, and 18000 to 162000 t N at the inshore stations (Himmerfjärden). Rates of N2 fixation were measured in situ at 4 depths between 0 and 25 m using the 15N tracer technique for size fractionated organisms larger and smaller than 20 µm. Maximum rates of N2 fixation were found in surface waters (0 to 4 m depth), and a major part of this activity (80% in coastal and 89% in offshore waters) took place during daylight hours. Integrated rates of N2 fixation in cells >20 µm followed the average abundance of filamentous cyanobacteria (primarily Aphanizomenon sp.) in the water column. Molar C:N mass ratios in particles >20 µm, i.e. filamentous cyanobacteria, suggest that this size fraction was N-sufficient during summer, whereas the molar C:P mass ratios indicated P-limitation during this period. A reduction in sewage discharge to the Himmerfjärden bay area during the study period appears not to have been compensated for by increased rates of N2 fixation. The patchy distribution of cyanobacteria and the high seasonal variability in N2 fixation rates emphasize the need for adequate spatial and temporal sampling strategies in studies of N2 fixation in coastal and open waters of the Baltic Sea.

  • 146.
    Dehghani, Reihaneh
    et al.
    Stockholm University, Faculty of Science, Department of Zoology. Systematik och evolutionsforskning.
    Wanntorp, L.
    Department of Botany.
    Pagani, P.
    Källersjö, M.
    Werdelin, Lars
    Veron, G.
    Phylogeography of the white-tailed mongoose (Herpestidae, Carnivora, Mammalia) based on partial sequences of the mtDNA control region (p 385-393)2008In: Journal of Zoology, no 276, p. 385-393Article in journal (Refereed)
    Abstract [en]

    The phylogeography of the white-tailed mongoose Ichneumia albicauda is examined using phylogenetic analyses based on partial sequences of the mitochondrial control region. The phylogeny is used to: (1) Analyse the phylogeographic pattern of I. albicauda; (2) discuss the existing delimitation of subspecies; (3) test if the coloration of the tail tip, generally white but occasionally black in West African specimens, is a species polymorphism or if it has phylogenetic significance. Our results suggest a north–south division within white-tailed mongoose populations, and within the northern clade, we observe an east–west subdivision. This phylogenetic pattern is partly in concordance with the traditional division into six subspecies. The white-tailed mongoose probably originated in southern Africa, from where it dispersed northwards and colonized eastern and western parts of Africa, as well as the Arabian Peninsula. Colour polymorphism observed in Western populations reflects variation at the individual level.

  • 147. Delprete, P. G.
    et al.
    Achille, F.
    Mouly, A.
    Stockholm University, Faculty of Science, The Bergius Botanical Garden Museum. Stockholm University, Faculty of Science, Department of Botany.
    Four new combinations in Chomelia and Stenostomum (Rubiaceae, Guettardeae) from Central America, the Guianas and the Amazon Basin2010In: Blumea - Journal of plant taxonomy and plant geography, ISSN 0006-5196, E-ISSN 2212-1676, Vol. 55, no 2, p. 164-170Article in journal (Refereed)
    Abstract [en]

    According to current generic delimitations, supported by wood anatomy, palynology, and recent molecular phylogenies, Antirhea, traditionally treated as a Pantropical genus, is instead restricted to the Paleotropics. At the same time, the Neotropical species traditionally positioned in Antirhea should be positioned in Stenostomum. Following these definitions, Stenostomum is a genus with most of the species present in the Caribbean Region, and two species present in the Guianas, namely S. acreanum and S. guianensis, distributed throughout the Amazon Basin. In addition, according to these new generic delimitations, two species previously positioned in Guettarda and Antirhea need to be transferred to Chomelia, as C. triflora and C. ulei.

  • 148. Demchenko, K.
    et al.
    Zdyb, Anna
    Stockholm University, Faculty of Science, Department of Botany.
    Feussner, I.
    Pawlowski, Katharina
    Stockholm University, Faculty of Science, Department of Botany.
    Analysis of the subcellular localisation of lipoxygenase in legume and actinorhizal nodules2012In: Plant Biology, ISSN 1435-8603, E-ISSN 1438-8677, Vol. 14, no 1, p. 56-63Article in journal (Refereed)
    Abstract [en]

    Plant lipoxygenases (LOXs; EC 1.13.11.12) catalyse the oxygenation of polyunsaturated fatty acids, linoleic (18:2) and a-linolenic acid (18:3(n-3)) and are involved in processes such as stress responses and development. Depending on the regio-specificity of a LOX, the incorporation of molecular oxygen leads to formation of 9- or 13-fatty acid hydroperoxides, which are used by LOX itself as well as by members of at least six different enzyme families to form a series of biologically active molecules, collectively called oxylipins. The best characterised oxylipins are the jasmonates: jasmonic acid (JA) and its isoleucine conjugate that are signalling compounds in vegetative and propagative plant development. In several types of nitrogen-fixing root nodules, LOX expression and/or activity is induced during nodule development. Allene oxide cyclase (AOC), a committed enzyme of the JA biosynthetic pathway, has been shown to localise to plastids of nodules of one legume and two actinorhizal plants, Medicago truncatula, Datisca glomerata and Casuarina glauca, respectively. Using an antibody that recognises several types of LOX interspecifically, LOX protein levels were compared in roots and nodules of these plants, showing no significant differences and no obvious nodule-specific isoforms. A comparison of the cell-specific localisation of LOXs and AOC led to the conclusion that (i) only cytosolic LOXs were detected although it is generally assumed that the (13S)-hydroperoxy a-linolenic acid for JA biosynthesis is produced in the plastids, and (ii) in cells of the nodule vascular tissue that contain AOC, no LOX protein could be detected.

  • 149.
    Demina, Irina
    Stockholm University, Faculty of Science, Department of Botany.
    Differentiation of infected cells in root nodule symbioses2011Licentiate thesis, comprehensive summary (Other academic)
  • 150. Diez, Beatriz
    et al.
    Bergman, Birgitta
    Stockholm University, Faculty of Science, Department of Botany.
    El-Shehawy, Rehab
    Marine diazotrophic cyanobacteria: out of the blue.2008In: Plant Biotechnology, ISSN 1342-4580, Vol. 25, no 3, p. 221-225Article, review/survey (Other (popular science, discussion, etc.))
1234567 101 - 150 of 818
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