Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Globally intertwined evolutionary history of giant barrel sponges
    Swierts, Thomas ; Peijnenburg, Katja T.C.A. ; Leeuw, Christiaan A. de; Breeuwer, Johannes A.J. ; Cleary, Daniel F.R. ; Voogd, Nicole J. de - \ 2017
    Coral Reefs 36 (2017)3. - ISSN 0722-4028 - p. 933 - 945.
    Biogeography - Mitochondrial DNA - Nuclear DNA - Porifera - Species complex - Xestospongia
    Three species of giant barrel sponge are currently recognized in two distinct geographic regions, the tropical Atlantic and the Indo-Pacific. In this study, we used molecular techniques to study populations of giant barrel sponges across the globe and assessed whether the genetic structure of these populations agreed with current taxonomic consensus or, in contrast, whether there was evidence of cryptic species. Using molecular data, we assessed whether giant barrel sponges in each oceanic realm represented separate monophyletic lineages. Giant barrel sponges from 17 coral reef systems across the globe were sequenced for mitochondrial (partial CO1 and ATP6 genes) and nuclear (ATPsβ intron) DNA markers. In total, we obtained 395 combined sequences of the mitochondrial CO1 and ATP6 markers, which resulted in 17 different haplotypes. We compared a phylogenetic tree constructed from 285 alleles of the nuclear intron ATPsβ to the 17 mitochondrial haplotypes. Congruent patterns between mitochondrial and nuclear gene trees of giant barrel sponges provided evidence for the existence of multiple reproductively isolated species, particularly where they occurred in sympatry. The species complexes in the tropical Atlantic and the Indo-Pacific, however, do not form separate monophyletic lineages. This rules out the scenario that one species of giant barrel sponge developed into separate species complexes following geographic separation and instead suggests that multiple species of giant barrel sponges already existed prior to the physical separation of the Indo-Pacific and tropical Atlantic.
    Population genetic structure, abundance and health status of two dominant benthic species in the Saba Bank National Park, Caribbean Netherlands: Montastraea cavernosa and Xestospongia muta
    Bakker, D.M. de; Meesters, H.W.G. ; Bleijswijk, J.D.L. van; Luttikhuizen, P. ; Breeuwer, J.A.J. ; Becking, L.E. - \ 2016
    PLoS ONE 11 (2016)5. - ISSN 1932-6203 - 20 p.
    Saba Bank, a submerged atoll in the Caribbean Sea with an area of 2,200 km2, has attained international conservation status due to the rich diversity of species that reside on the bank. In order to assess the role of Saba Bank as a potential reservoir of diversity for the surrounding reefs, we examined the population genetic structure, abundance and health status of two prominent benthic species, the coral Montastraea cavernosa and the sponge Xestospongia muta. Sequence data were collected from 34 colonies of M. cavernosa (nDNA ITS1-5.8S-ITS2; 892 bp) and 68 X. muta sponges (mtDNA I3-M11 partition of COI; 544 bp) on Saba Bank and around Saba Island, and compared with published data across the wider Caribbean. Our data indicate that there is genetic connectivity between populations on Saba Bank and the nearby Saba Island as well as multiple locations in the wider Caribbean, ranging in distance from 100s–1000s km. The genetic diversity of Saba Bank populations of M. cavernosa (π = 0.055) and X. muta (π = 0.0010) was comparable to those in other regions in the western Atlantic. Densities and health status were determined along 11 transects of 50 m2 along the south-eastern rim of Saba Bank. The densities of M. cavernosa (0.27 ind. m-2, 95% CI: 0.12–0.52) were average, while the densities of X. muta (0.09 ind. m-2, 95% CI: 0.02–0.32) were generally higher with respect to other Caribbean locations. No disease or bleaching was present in any of the specimens of the coral M. cavernosa, however, we did observe partial tissue loss (77.9% of samples) as well as overgrowth (48.1%), predominantly by cyanobacteria. In contrast, the majority of observed X. muta (83.5%) showed signs of presumed bleaching. The combined results of apparent gene flow among populations on Saba Bank and surrounding reefs, the high abundance and unique genetic diversity, indicate that Saba Bank could function as an important buffer for the region. Either as a natural source of larvae to replenish genetic diversity or as a storehouse of diversity that can be utilized if needed for restoration practices
    Symbiotic bacteria (Erwinia sp.) in the gut of Frankliniella occidentalis (Thysanoptera: Thripidae) do not affect its ability to transmit tospovirus
    Vries, E.J. de; Wetering, F. van de; Hoek, M.M. van der; Jacobs, G. ; Breeuwer, J.A.J. - \ 2012
    European Journal of Entomology 109 (2012)2. - ISSN 1210-5759 - p. 261 - 266.
    western flower thrips - spotted wilt virus - insect vector - protein - tabaci
    Tomato spotted wilt virus (TSWV) is one of the most harmful plant viruses and one of its most important vectors is the western flower thrips [Frankliniella occidentalis Pergande (Thysanoptera: Thripidae)]. Recently, we reported the close association of Erwinia sp. gut bacteria with this species of thrips. The first instar larvae acquire these bacteria from their food source. A high proportion of adult western flower thrips transmit TSWV after acquiring the virus during the first larval stage when there are no bacteria in their gut. A considerably lower proportion of adults that acquire the virus early in the second instar transmit virus and none of those exposed to virus late on in the second instar do so. The highest prevalence and total number of symbiotic bacteria are recorded in the guts of second instar thrips. This leads to the hypothesis that the build up of bacteria in the gut reduces the acquisition of TSWV, resulting in a lower capacity to transmit the virus. To test this hypothesis, the transmission of this virus by symbiotic and aposymbiotic adult thrips of the NL3 population was studied. Comparison of virus transmission by adult thrips, the larvae of which either had or lacked gut bacteria and were exposed to virus in either the first or second instar, revealed no difference in the ability of symbiotic and aposymbiotic adults to transmit this virus. We conclude that virus transmission is not affected by the number of the symbiotic bacteria Erwinia sp. present in the gut of thrips larvae
    Glasshouse vs field experiments: do they yield ecologically similar results for assessing N impacts on peat mosses
    Limpens, J. ; Granath, G. ; Gunnarsson, U. ; Rydin, H. ; Aerts, R. ; Heijmans, M.M.P.D. ; Hoosbeek, M.R. ; Paulissen, M.P.C.P. ; Breeuwer, A.J.G. - \ 2012
    New Phytologist 195 (2012)2. - ISSN 0028-646X - p. 408 - 418.
    nitrogen deposition - sphagnum mosses - metaanalysis - peatlands - carbon - scale - responses - ecology - cycle
    • Peat bogs have accumulated more atmospheric carbon (C) than any other terrestrial ecosystem today. Most of this C is associated with peat moss (Sphagnum) litter. Atmospheric nitrogen (N) deposition can decrease Sphagnum production, compromising the C sequestration capacity of peat bogs. The mechanisms underlying the reduced production are uncertain, necessitating multifactorial experiments. • We investigated whether glasshouse experiments are reliable proxies for field experiments for assessing interactions between N deposition and environment as controls on Sphagnum N concentration and production. We performed a meta-analysis over 115 glasshouse experiments and 107 field experiments. • We found that glasshouse and field experiments gave similar qualitative and quantitative estimates of changes in Sphagnum N concentration in response to N application. However, glasshouse-based estimates of changes in production – even qualitative assessments – diverged from field experiments owing to a stronger N effect on production response in absence of vascular plants in the glasshouse, and a weaker N effect on production response in presence of vascular plants compared to field experiments. • Thus, although we need glasshouse experiments to study how interacting environmental factors affect the response of Sphagnum to increased N deposition, we need field experiments to properly quantify these effects.
    Diversity and recombination in Wolbachia and Cardinium from Bryobia spider mites
    Ros, V.I.D. ; Fleming, V.M. ; Feil, E.J. ; Breeuwer, J.A.J. - \ 2012
    BMC Microbiology 12 (2012)Suppl. 1. - ISSN 1471-2180 - 15 p.
    cytoplasmic incompatibility - tetranychus-urticae - horizontal transfer - bacteriophage-wo - endosymbionts wolbachia - arthropod endosymbiont - reproductive parasites - neisseria-meningitidis - relative contributions - evolutionary history
    Background Wolbachia and Cardinium are endosymbiotic bacteria infecting many arthropods and manipulating host reproduction. Although these bacteria are maternally transmitted, incongruencies between phylogenies of host and parasite suggest an additional role for occasional horizontal transmission. Consistent with this view is the strong evidence for recombination in Wolbachia, although it is less clear to what extent recombination drives diversification within single host species and genera. Furthermore, little is known concerning the population structures of other insect endosymbionts which co-infect with Wolbachia, such as Cardinium. Here, we explore Wolbachia and Cardinium strain diversity within nine spider mite species (Tetranychidae) from 38 populations, and quantify the contribution of recombination compared to point mutation in generating Wolbachia diversity. Results We found a high level of genetic diversity for Wolbachia, with 36 unique strains detected (64 investigated mite individuals). Sequence data from four Wolbachia genes suggest that new alleles are 7.5 to 11 times more likely to be generated by recombination than point mutation. Consistent with previous reports on more diverse host samples, our data did not reveal evidence for co-evolution of Wolbachia with its host. Cardinium was less frequently found in the mites, but also showed a high level of diversity, with eight unique strains detected in 15 individuals on the basis of only two genes. A lack of congruence among host and Cardinium phylogenies was observed. Conclusions We found a high rate of recombination for Wolbachia strains obtained from host species of the spider mite family Tetranychidae, comparable to rates found for horizontally transmitted bacteria. This suggests frequent horizontal transmission of Wolbachia and/or frequent horizontal transfer of single genes. Our findings strengthens earlier reports of recombination for Wolbachia, and shows that high recombination rates are also present on strains from a restrictive host range. Cardinium was found co-infecting several spider mite species, and phylogenetic comparisons suggest also horizontal transmission of Cardinium among hosts
    Cardinium: the next addition to the family of reproductive parasites
    Breeuwer, J.A.J. ; Ros, V.I.D. ; Groot, T.V.M. - \ 2011
    In: Manipulative tenants: Bacteria associated with arthropods / Zchori-Fein, E., Bourtzis, K., London : CRC Press - ISBN 9781439827499 - p. 207 - 219.
    How will peat bogs respond to climate change? Results of combined palaeo-ecological, experimental and model research
    Heijmans, M.M.P.D. ; Breeuwer, A.J.G. ; Linden, M. van der; Geel, B. van; Berendse, F. - \ 2011
    In: Proceedings of Netherlands Annual Ecology Meeting, 8-9 February 2011, Lunteren, The Netherlands. - - p. 7 - 7.
    Lack of evidence for western flower thrips biotypes base don intra and inter-strain variation in gut bacteria
    Vries, E.J. de; Jacobs, G. ; Kogel, W.J. de; Hoek, M. van der; Breeuwer, J.A.J. - \ 2010
    In: Symbiosis of thrips and gutbacteria, PhD thesis van E.J. de Vries Amsterdam : Universiteit van Amsterdam, Faculty of Science - ISBN 9789076894850 - p. 110 - 124.
    Western flower thrips is a polyphagous insect, which during the last 30 years has become a world wide pest. It was found earlier that these thrips are associated with a type of Erwinia species gut bacteria. In this study we examine the variation of bacteria within and between thrips individuals and try to find evidence for biotypes in western flower thrips regarding the type of gut bacteria. The existence of biotypes in this thrips species has been suggested by different authors. For example, thrips populations have been found that differ in resistance against pesticides and in their ability to transmit plant viruses. With biotypes we mean groups of individuals (strains, populations, lines) of a species which differ in one or more traits with other groups of that species. The gut bacteria of thrips are acquired by young thrips larvae via the host plant and have a beneficial effect on thrips development and oviposition. We studied thrips strains from different countries and host plants, and the isofemale lines that were created from them, on bean plant leaves. All thrips lines that we studied contained Erwinia species gut bacteria. Morphological and biochemical characteristics of gut bacteria from the thrips isofemale lines were similar to the Erwinia type strain from the reference, a thrips strain cultured on chrysanthemum in Amsterdam (TAC 93.XII.8). Per isofemale line we studied five thrips individuals and per thrips we studied four bacterial colonies, with RAPD markers. The genetic variation between bacteria isolated from thrips was as large among isofemale lines as within isofemale lines. No evidence for thrips biotypes was found. Bacteria within one thrips individual show a stronger degree of similarity than bacteria from different thrips individuals within a single rearing. This is probably due to a bottleneck caused by the limited number of successful infections of bacteria into the gut of the thrips
    Diversity and transmission of Wolbachia in spider mites
    Ros, V.I.D. ; Fleming, V.M. ; Feil, E.J. ; Breeuwer, J.A.J. - \ 2010
    In: Proceedings of the 43rd Annual Meeting of the Society of Invertebrate Pathology, Trabzon, Turkey, 11-15 July 2010. - - p. 154 - 154.
    Field Simulation of Global Change: Transplanting Northern Bog Mesocosms Southward
    Breeuwer, A.J.G. ; Heijmans, M.M.P.D. ; Robroek, B.J.M. ; Berendse, F. - \ 2010
    Ecosystems 13 (2010)5. - ISSN 1432-9840 - p. 712 - 726.
    increased nitrogen deposition - increased n deposition - water-table depth - vascular plants - sphagnum mosses - litter quality - climate-change - boreal mire - peat bogs - mass-loss
    A large proportion of northern peatlands consists of Sphagnum-dominated ombrotrophic bogs. In these bogs, peat mosses (Sphagnum) and vascular plants occur in an apparent stable equilibrium, thereby sustaining the carbon sink function of the bog ecosystem. How global warming and increased nitrogen (N) deposition will affect the species composition in bog vegetation is still unclear. We performed a transplantation experiment in which mesocosms with intact vegetation were transplanted southward from north Sweden to north-east Germany along a transect of four bog sites, in which both temperature and N deposition increased. In addition, we monitored undisturbed vegetation in control plots at the four sites of the latitudinal gradient. Four growing seasons after transplantation, ericaceous dwarf shrubs had become much more abundant when transplanted to the warmest site which also had highest N deposition. As a result ericoid aboveground biomass in the transplanted mesocosms increased most at the southernmost site, this site also had highest ericoid biomass in the undisturbed vegetation. The two dominant Sphagnum species showed opposing responses when transplanted southward; Sphagnum balticum height increment decreased, whereas S. fuscum height increment increased when transplanted southward. Sphagnum production did not differ significantly among the transplanted mesocosms, but was lowest in the southernmost control plots. The dwarf shrub expansion and increased N concentrations in plant tissues we observed, point in the direction of a positive feedback toward vascular plant-dominance suppressing peat-forming Sphagnum in the long term. However, our data also indicate that precipitation and phosphorus availability influence the competitive balance between Sphagnum, dwarf shrubs and graminoids.
    How diverse is the genus Wolbachia? Multiple-gene sequencing reveals a putatively new Wolbachia supergroup recovered from spider mites (Acari: Tetranychidae)
    Ros, V.I.D. ; Fleming, V. ; Feil, E.J. ; Breeuwer, J.A.J. - \ 2009
    Applied and Environmental Microbiology 75 (2009)4. - ISSN 0099-2240 - p. 1036 - 1043.
    phylogenetic analysis - cytoplasmic incompatibility - reproductive incompatibility - bacterium wolbachia - filarial nematodes - dna amplification - genome sequence - f-supergroup - pipientis - arthropods
    At least 20% of all arthropods and some nematode species are infected with intracellular bacteria of the genus Wolbachia. This highly diverse genus has been subdivided into eight “supergroups” (A to H) on the basis of nucleotide sequence data. Here, we report the discovery of a new Wolbachia supergroup recovered from the spider mite species Bryobia species V (Acari: Tetranychidae), based on the sequences of three protein-coding genes (ftsZ, gltA, and groEL) and the 16S rRNA gene. Other tetranychid mites possess supergroup B Wolbachia strains. The discovery of another Wolbachia supergroup expands the known diversity of Wolbachia and emphasizes the high variability of the genus. Our data also clarify the existing supergroup structure and highlight the use of multiple gene sequences for robust phylogenetic analysis. In addition to previous reports of recombination between the arthropod-infecting supergroups A and B, we provide evidence for recombination between the nematode-infecting supergroups C and D. Robust delineation of supergroups is essential for understanding the origin and spread of this common reproductive parasite and for unraveling mechanisms of host adaptation and manipulation across a wide range of hosts
    The effects of, and interactions between, Cardinium and Wolbachia in the doubly infected spider mite Bryobia sarothamni (Acari: Tetranychidae)
    Ros, V.I.D. ; Breeuwer, J.A.J. - \ 2009
    Heredity 102 (2009)4. - ISSN 0018-067X - p. 413 - 422.
    induced cytoplasmic incompatibility - tetranychus-urticae - drosophila-simulans - host genotype - nasonia-vitripennis - bacterial symbiont - haplodiploid mite - dna amplification - genome sequence - fecundity
    Many arthropods are infected with vertically transmitted, intracellular bacteria manipulating their host's reproduction. Cytoplasmic incompatibility (CI) is commonly observed and is expressed as a reduction in the number of offspring in crosses between infected males and uninfected females (or females infected with a different bacterial strain). CI is often related to the presence of Wolbachia, but recent findings indicate that a second reproductive parasite, Cardinium, is also capable of inducing CI. Although both Wolbachia and Cardinium occur in arthropods and may infect the same host species, little is known about their interactions. We observed Wolbachia and Cardinium in the sexual spider mite Bryobia sarothamni (Acari: Tetranychidae) and investigated the effects of both bacteria on reproduction. We performed all possible crossing combinations using naturally infected strains, and show that Cardinium induces strong CI, expressed as an almost complete female mortality. B. sarothamni is the third host species in which Cardinium-induced CI is observed, and this study reveals the strongest CI effect found so far. Wolbachia, however, did not induce CI. Even so, CI was not induced by doubly infected males, and neither singly Wolbachia-infected nor doubly infected females could rescue CI induced by Cardinium-infected males. Possibly, this is related to the differences between Cardinium strains infecting singly and doubly infected individuals. We found a cost of infection in single infected individuals, but not in doubly infected individuals. We show that infection frequencies in field populations ranged from completely uninfected to a polymorphic state. In none of the populations infections were fixed
    Growth of Cronobacter spp. under dynamic temperature conditions occurring during cooling of reconstituted powdered infant formula
    Kandhai, M.C. ; Breeuwer, P. ; Peters, E.G. ; Gorris, L.G.M. ; Zwietering, M.H. ; Reij, M.W. - \ 2009
    In: 6th International Conference Predictive Modeling in Foods Meeting, Washington DC, USA, September 8-12, 2009. - Organizing Committee for the 6th International Conference on Predictive Modeling in Foods - p. 46 - 46.
    Growth of Cronobacter spp. under Dynamic Temperature Conditions Occurring during Cooling of Reconstituted Powdered Infant Formula
    Kandhai, M.C. ; Breeuwer, P. ; Gorris, L.G.M. ; Zwietering, M.H. ; Reij, M.W. - \ 2009
    Journal of Food Protection 72 (2009)12. - ISSN 0362-028X - p. 2489 - 2498.
    enterobacter-sakazakii - domestic refrigerators - neonatal meningitis - milk - performance - convection - foods - time
    Reconstituted infant formulae are excellent growth media for Cronobacter spp. (formerly Enterobacter sakazakii) and other microorganisms that may be present in such products. Immediate consumption or rapid cooling and storage at a low temperature are therefore recommended as control measures to prevent microbial growth. Placing a container filled with reconstituted liquid formula in the refrigerator, however, does not mean that the temperature of the liquid is directly the same as the set-point of the refrigerator. This study describes the temperature profiles and methods to predict lag time and possible growth of Cronobacter spp. during the cooling process in three types of containers. The overall heat transfer coefficients (a) were determined and were shown to have a very large variability in both household refrigerators and an air-ventilated refrigerator equipped with a fan. A mathematical model was built to predict the growth of Cronobacter spp. under dynamic temperature conditions using three models for the lag time. The various estimations for the lag time had a remarkably strong impact on the predicted growth. The assumption of a constant k-value (k = lag time × specific growth rate = ¿ × µ = 2.88) fitted the experimental data best. Predictions taking into account the large variability in heat transfer showed that proliferation of Cronobacter spp. during cooling may be prevented by limiting the volume to be cooled to portion size only, or by reconstituting at temperatures of 25°C or lower. The model may also be used to predict growth in other situations where dynamic temperature conditions exist.
    How atmospheric N deposition affects peatland vegetation composition, production and Sphagnum N concentration: an analysis of 30 fertilization sturdies across the Northern Hemisphere
    Limpens, J. ; Granath, G. ; Gunnarsson, U. ; Aerts, R. ; Bragazza, L. ; Breeuwer, A.J.G. ; Bubier, J. ; Berg, L. van den; Franchez, A.J. ; Gerdol, R. ; Heijmans, M.M.P.D. ; Hoosbeek, M.R. ; Hotes, S. ; Ilomets, M. ; Mitchell, E. ; Moore, T. ; Nilsson, M. ; Nordbakken, J.F. ; Paulissen, M.P.C.P. ; Risager, M. ; Rochefort, L. ; Rydin, H. ; Sheppard, L. ; Thormann, M. ; Tomassen, H. ; Williams, B. - \ 2009
    In: Working Papers of the Finnish Forest Research Institute 128, Proceedings of the 6th International Symposium on Ecosystem Behaviour BIOGEOMON 2009, Helsinki, Finland, 29 June - 3 July 2009. - Vantaa, Finland : Finnish Forest Research Institute - ISBN 9789514021763 - p. 251 - 251.
    Do meadow birds profit from agri-environment schemes in Dutch agricultural landscapes?
    Breeuwer, A.J.G. ; Berendse, F. ; Willems, F. ; Foppen, R. ; Teunissen, W. ; Schekkerman, H. ; Goedhart, P.W. - \ 2009
    Biological Conservation 142 (2009)12. - ISSN 0006-3207 - p. 2949 - 2953.
    godwit limosa-limosa - farmland - biodiversity - intensification - management - abundance - success
    Since 1992 the European Union helps member states to reverse the loss of biodiversity in agricultural landscapes by the financial support of agri-environment schemes. Long-term studies investigating the effects of these schemes are an essential prerequisite for the development of an effective policy to restore biodiversity on farmland. In Dutch meadow landscapes almost all agri-environment schemes focus on the restoration of meadow bird populations by postponement of the mowing date. Between 1990 and 2002 we measured long-term changes in meadow bird densities in areas with and without agri-environment schemes in the Netherlands, both before and after the start of the contract. During these years bird territories were surveyed during five field visits between 15 March and 15 June. Densities of black-tailed godwit (Limosa limosa), and redshank (Tringa totanus) were higher in the areas with management agreements, but these differences were already present before the start of the contracts. After the start of the management contracts densities of black-tailed godwit and oystercatcher (Haematopus ostralegus) did not increase, while those of lapwing (Vanellus vanellus) and redshank even declined relative to the control areas. It is concluded that the current agri-environment schemes are not sufficient to restore meadow bird populations in Dutch agricultural landscapes. In addition to the prescribed postponement of the mowing date, it is probably necessary to raise groundwater levels and to reduce fertilization to allow for the development of an open vegetation structure that will increase chick survival to sufficiently high levels
    Sphagnum re-introduction in degraded peatlands: the effects of aggregation, species and water table
    Robroek, B.J.M. ; Ruijven, J. van; Schouten, M.G.C. ; Breeuwer, A.J.G. ; Crushell, P.H. ; Berendse, F. ; Limpens, J. - \ 2009
    Basic and Applied Ecology 10 (2009)8. - ISSN 1439-1791 - p. 697 - 706.
    experimental plant-communities - interspecific competition - vascular plants - growth - bog - mosses - heterogeneity - restoration - vegetation - dynamics
    In European peatlands which have been drained and cut-over in the past, re-vegetation often stagnates after the return of a species-poor Sphagnum community. Re-introduction of currently absent species may be a useful tool to restore a typical, and more diverse, Sphagnum vegetation and may ultimately improve the functioning of peatland ecosystems, regarding atmospheric carbon sequestration. Yet, the factors controlling the success of re-introduction are unclear. In Ireland and Estonia, we transplanted small and large aggregates of three Sphagnum species into existing vegetation. We recorded changes in cover over a 3-year period, at two water levels (¿5 and ¿20 cm). Performance of transplanted aggregates of Sphagnum was highly species specific. Hummock species profited at low water tables, whereas hollow species profited at high water tables. But our results indicate that performance and establishment of species was also promoted by increased aggregate size. This mechanism (positive self-association) has earlier been seen in other ecosystems, but our results are the first to show this mechanism in peatlands. Our results do not agree with present management, which is aimed at retaining water on the surface of peat remnants in order to restore a functional and diverse Sphagnum community. More than the water table, aggregate size of the reintroduced species is crucial for species performance, and ultimately for successful peatland restoration.
    Response of Sphagnum species mixtures to increased temperature and nitrogen availability
    Breeuwer, A.J.G. ; Heijmans, M.M.P.D. ; Berendse, F. ; Gleichman, J.M. ; Robroek, B.J.M. ; Limpens, J. - \ 2009
    Plant Ecology 204 (2009)1. - ISSN 1385-0237 - p. 97 - 111.
    n-deposition - water-level - nutritional constraints - decomposition rates - northern peatlands - litter quality - climate-change - peat formation - growth - bogs
    To predict the role of ombrotrophic bogs as carbon sinks in the future, it is crucial to understand how Sphagnum vegetation in bogs will respond to global change. We performed a greenhouse experiment to study the effects of two temperature treatments (17.5 and 21.7°C) and two N addition treatments (0 and 4 g N m¿2 year¿1) on the growth of four Sphagnum species from three geographically interspersed regions: S. fuscum, S. balticum (northern and central Sweden), S. magellanicum and S. cuspidatum (southern Sweden). We studied the growth and cover change in four combinations of these Sphagnum species during two growing seasons. Sphagnum height increment and production were affected negatively by high temperature and high N addition. However, the northern species were more affected by temperature, while the southern species were more affected by N addition. High temperature depressed the cover of the `wet¿ species, S. balticum and S. cuspidatum. Nitrogen concentrations increased with high N addition. N:P and N:K ratios indicated P-limited growth in all treatments and co-limitation of P and K in the high N treatments. In the second year of the experiment, several containers suffered from a severe fungal infection, particularly affecting the `wet¿ species and the high N treatment. Our findings suggest that global change can have negative consequences for the production of Sphagnum species in bogs, with important implications for the carbon sequestration in these ecosystems
    Photosynthetic performance in Sphagnum transplanted along a latitudinal nitrogen deposition gradient
    Granath, G. ; Strengbom, J. ; Breeuwer, A.J.G. ; Heijmans, M.M.P.D. ; Berendse, F. ; Rydin, H. - \ 2009
    Oecologia 159 (2009)4. - ISSN 0029-8549 - p. 705 - 715.
    atmospheric nitrogen - n deposition - boreal mire - chlorophyll fluorescence - physiological-responses - parasitic fungus - water-content - growth - mosses - vegetation
    Increased N deposition in Europe has affected mire ecosystems. However, knowledge on the physiological responses is poor. We measured photosynthetic responses to increasing N deposition in two peatmoss species (Sphagnum balticum and Sphagnum fuscum) from a 3-year, north-south transplant experiment in northern Europe, covering a latitudinal N deposition gradient ranging from 0.28 g N m(-2) year(-1) in the north, to 1.49 g N m(-2) year(-1) in the south. The maximum photosynthetic rate (NPmax) increased southwards, and was mainly explained by tissue N concentration, secondly by allocation of N to the photosynthesis, and to a lesser degree by modified photosystem II activity (variable fluorescence/maximum fluorescence yield). Although climatic factors may have contributed, these results were most likely attributable to an increase in N deposition southwards. For S. fuscum, photosynthetic rate continued to increase up to a deposition level of 1.49 g N m(-2) year(-1), but for S. balticum it seemed to level out at 1.14 g N m(-2) year(-1). The results for S. balticum suggested that transplants from different origin (with low or intermediate N deposition) respond differently to high N deposition. This indicates that Sphagnum species may be able to adapt or physiologically adjust to high N deposition. Our results also suggest that S. balticum might be more sensitive to N deposition than S. fuscum. Surprisingly, NPmax was not (S. balticum), or only weakly (S. fuscum) correlated with biomass production, indicating that production is to a great extent is governed by factors other than the photosynthetic capacity.
    Decreased summer water table depth affects peatland vegetation
    Breeuwer, A.J.G. ; Robroek, B.J.M. ; Limpens, J. ; Heijmans, M.M.P.D. ; Schouten, M.G.C. ; Berendse, F. - \ 2009
    Basic and Applied Ecology 10 (2009)4. - ISSN 1439-1791 - p. 330 - 339.
    sphagnum mosses - nitrogen deposition - vascular plants - interspecific competition - decomposition rates - bog vegetation - n deposition - community - level - co2
    Climate change can be expected to increase the frequency of summer droughts and associated low water tables in ombrotrophic peatlands. We studied the effects of periodic water table drawdown in a mesocosm experiment. Mesocosms were collected in Southern Sweden, and subsequently brought to an experimental field in the Netherlands. Two water table treatments were applied: one with constant water tables at 5 cm below the moss surface, and one in which the water table was allowed to drop, resulting in water tables fluctuating between 5 and 21 cm below the moss surface. Sphagnum growth, as well as Sphagnum and vascular plant abundance, were assessed for years. Our results show that the abundance of graminoid species increased most in the constant water table treatment. In contrast, ericoid species cover increased when water tables were allowed to fluctuate. Furthermore, Sphagnum cuspidatum production decreased with fluctuating summer water tables, while Sphagnum magellanicum responded oppositely. From these results we conclude that increased occurrence of periods with low water tables may bring about a shift in dominant Sphagnum species as well as a shift from graminoid to ericoid vascular plant cover, resembling the shift from hollow to lawn or hummock vegetation. The difference in response within functional groups (vascular plants, Sphagnum) may add to the resilience of the ecosystem.
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