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.

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Do plant traits explain tree seedling survival in bogs?
Limpens, J. ; Egmond, E. van; Li, B. ; Holmgren, M. - \ 2014
Functional Ecology 28 (2014)1. - ISSN 0269-8463 - p. 283 - 290.
sphagnum mosses - picea-mariana - water-table - scots pine - boreal - growth - peatlands - recruitment - establishment - carbon
1.Moss-dominated peat bogs store approximately 30% of global soil carbon. A climate induced shift from current moss-dominated conditions to tree-dominated states is expected to strongly affect their functioning and carbon sequestration capacity. Consequently, unraveling the mechanisms that may explain successful tree seedling establishment in these ecosystems is highly relevant. 2.To assess the role of drought on early tree seedling establishment and the relative importance of plant traits in tree seedling survival, we conducted a factorial glasshouse experiment with seven conifer species. 3.Our results show that drought inhibits moss growth, thereby increasing survival of tree seedlings. Survival success was higher in Pinus than in Picea species, ranking Pinus banksiana > Pinus sylvestris > Pinus nigra > Picea mariana > Picea glauca, Picea sitchensis > Picea rubens. We found that those species most successful under dry and wet conditions combined a fast shoot growth with high seed mass. 4.We conclude that plant traits contribute to explaining successful early tree seedling establishment in bogs
Surviving and growing amidst others : the effect of environmental factors on germination and establishment of savanna trees
Moribe Barbosa, E.R. - \ 2013
University. Promotor(en): Herbert Prins; Steven Bie, co-promotor(en): Frank van Langevelde. - S.l. : s.n. - ISBN 9789461734655 - 125
bomen - savannen - kieming - milieufactoren - vestiging - concurrentie tussen planten - zaailingen - plantenontwikkeling - plantenecologie - trees - savannas - germination - environmental factors - establishment - plant competition - seedlings - plant development - plant ecology

Savanna ecosystems are characterized by a continuous grass layer intermixed with a discontinuous layer of trees and shrubs. A complex set of environmental drivers, such as water, soil nutrients, solar radiance, fire and herbivory, determines vegetation structure and composition in savannas.Such environmental drivers are expected to be strongly affected by future global climatic and land-use changes, potentially modifying savanna vegetation, and consequently savanna fauna. The ability to predict changes in plant community composition is therefore importantfor management and conservation of savannas. However, the mechanisms controlling plant establishment and growth in savannas are still unclear. Germination and seedling establishment are critical recruitment stages in the life cycle of plants and can influence plant community composition. A better understand of the factors influencing plant species recruitment and their ecology is needed. This thesis focuses on seedling recruitment of several savanna tree species.

Water stress is probably the single greatest constraint to tree seedling survival in savanna systems: tree seedling recruitment and survival are hypothesized to be limited by soil moisture availability. Shade by established adult trees may facilitate tree seedling recruitment by maintaining high soil moisture availability. Chapter 2 deals with germination and early seedling establishment of several tree species. I expected that tree species would germinate and establish best under high moisture conditions (high water and shade), while under stress conditions (i.e. low soil moisture due to low water supply and full sun, and in the presence of grasses) plants would suffer. The observed variability of seedling performance among the tree species under stress conditions may be explained by differences in functional traits. Higher soil moisture mostly benefited germination of species with seeds with high calcium concentration and low water content. On the other hand, low soil moisture conditions benefited germination of tree species with seeds with higher magnesium and phosphorus concentration and water content. Furthermore, under low soil moisture availability, grass presence facilitated germination of most tree species but its effect on early survival (positive or negative) differed among species. The findings of this chapter confirm a large difference in the tree species responses to environmental variation during early recruitment, which potentially affect theplant community composition and dynamics under different environmental conditions in savannas.Seed trait differences among the species partly contribute to explain such variability. Therefore, considering inter-specific variation among tree species and information on seed traits can improve the ability to predict and manage the impacts of environment changes.

For later stages of seedling development (up to 9 months), the effect of environmental variation (water, nutrient and light supply, as well as grass presence or absence) on survival and establishment of semi-arid savanna tree seedlings differed between species (Chapter 3). All species were expected to respond positively to higher resource availability, and negatively to the presence of grass. Indeed, the results of this chapterclearly show that grass presence strongly suppressed seedling establishment. However, recruitment strategies varied among species, particularly under high stress conditions (water stress or low light). In some of the studied tree species, light shortage (i.e., shade) reduced the negative effects of the presence of grass on growth. Furthermore, nutrient availability also reduced the negative effect of grasses, although for certain species (broad-leaf species) this effect occurred only under natural rainfall, while for others (fine-leaf species) it occurred only under regular water provision.

Increased atmospheric nitrogen deposition, intensification of agricultural fertilizer use and large herbivore management interventions are on-going processes that increase soil nutrient levels in many savannas. As nutrient concentration in the leaves (i.e., plant quality for herbivores) also depends on soil nutrient availability, I expected in Chapter 4 that both biomass production and leaf nutrient concentration would increase with increasing soil nutrient availability. Contrary to my expectations, differences in soil nutrient levels (low vs. high) did not affect biomass production of any of the tree species, independently of water availability (uneven vs. even water supply). However, leaf nutrient content of the seedlings did differ significantly with different water and nutrient levels. Soil nutrient input increased leaf nutrient content, but only when water was applied regularly, indicating that plant nutrient uptake strongly depends on water availability. Under irregular rainfall patterns, nutrient input significantly reduced leaf quality. Given that large herbivore populations depend on plant nutrient content for their nutritional requirements, increases in nutrient deposition and rainfall levels will likely impact herbivore populations and their browsing patterns, altering the functional structure of ecosystems even if overall plant biomass remains unaffected.

In Chapter 5, the effect of fluctuations of environmental conditions on above and belowground growth of juveniles of three savannas tree species (Acacia karroo, A. nigrescens and Colophospermum mopane) during the first 18 months was tested. While it was expected that low soil resource availability would result in high biomass allocation towards roots, experimental simulation of dry eventswithin the wet season or pulses of nutrient availability did not have a clear effect on the seedlings’ aboveground and belowground growth. Furthermore, the results of this chapter demonstrated that browsing stimulated stem regrowth and root elongation of savanna tree seedlings, suggesting that the three studied species have compensatory growth in response to frequent herbivory, quickly recovering the loss of biomass. This result puts in question the usefulness of herbivory or human land-cleaning in controlling invasive woody species in tropical grasslands and savannas.

In conclusion, the results of this thesis demonstrated that savanna tree species are generally able to cope with differences in resource availability during seedling establishment, being mostly limited by grass competition for resource. Furthermore, this study shows that during early stages of the life-cycle, when exposed to the same environmental conditions, tree species within a plant community differ in their responses, only having advantages over other species under specific conditions.This inter-specific variation may allow tree species coexistence, explaining the diversity of plant species in savannas.

Seasonal light interception, radiation use efficiency, growth and tuber production of the tuber crop Plectranthus edulis
Taye, M. ; Lommen, W.J.M. ; Struik, P.C. - \ 2013
European Journal of Agronomy 45 (2013). - ISSN 1161-0301 - p. 153 - 164.
enset ensete-ventricosum - dry-matter production - southern ethiopia - field performance - potato minitubers - seed tubers - yield - establishment - emergence - nitrogen
Plectranthus edulis (Vatke) Agnew (Lamiaceae) is an ancient Ethiopian crop that produces below-ground, edible tubers on stolons. It is grown from seed tuber pieces. There is thus far little quantitative information on dry matter production of this crop and parameters determining growth and yield. The objective of this study was to understand and quantify the growth of P. edulis, and identify the processes determining and limiting yield. Two similar experiments were carried out at two sites (Awassa and Wondogenet in southern Ethiopia) in a split-plot design with five blocks and cultivar (Lofuwa and Chankua) as main factor and sampling date [20 2-weekly sampling dates from 14 to 280 days after planting (DAP)] as split factor. The crop was unknown at the start and showed an unusual growth pattern, for which reasons growth was analysed at a basic level.
Quality of core collections for effective utilisation of genetic resources review, discussion and interpretation
Odong, T.L. ; Jansen, J. ; Eeuwijk, F.A. van; Hintum, T.J.L. van - \ 2013
Theoretical and Applied Genetics 126 (2013)2. - ISSN 0040-5752 - p. 289 - 305.
morphological descriptors - germplasm collection - sampling strategies - diversity - algorithm - establishment - accessions - selection - markers - sorghum
Definition of clear criteria for evaluation of the quality of core collections is a prerequisite for selecting high-quality cores. However, a critical examination of the different methods used in literature, for evaluating the quality of core collections, shows that there are no clear guidelines on the choices of quality evaluation criteria and as a result, inappropriate analyses are sometimes made leading to false conclusions being drawn regarding the quality of core collections and the methods to select such core collections. The choice of criteria for evaluating core collections appears to be based mainly on the fact that those criteria have been used in earlier publications rather than on the actual objectives of the core collection. In this study, we provide insight into different criteria used for evaluating core collections. We also discussed different types of core collections and related each type of core collection to their respective evaluation criteria. Two new criteria based on genetic distance are introduced. The consequences of the different evaluation criteria are illustrated using simulated and experimental data. We strongly recommend the use of the distance-based criteria since they not only allow the simultaneous evaluation of all variables describing the accessions, but they also provide intuitive and interpretable criteria, as compared with the univariate criteria generally used for the evaluation of core collections. Our findings will provide genebank curators and researchers with possibilities to make informed choices when creating, comparing and using core collections
Long-term effects of scrub clearance and litter removal on the re-establishment of dry alvar grassland species
Bakker, J.P. ; Rosén, E. ; Ozinga, W.A. ; Bretfeld, M. ; Feldt, T. ; Stahl, J. - \ 2012
Annales Botanici Fennici 49 (2012)1-2. - ISSN 0003-3847 - p. 21 - 30.
northwest european flora - life-history traits - chalk grassland - seedling recruitment - limestone grassland - plant-communities - bryophyte layer - establishment - dispersal - emergence
Many characteristic dry alvar grassland species disappear after cessation of livestock grazing as a result of encroachment by Juniperus communis. We studied the re-establishment of these species after scrub clearance with and without the removal of the layer of litter and mosses in long-term (14 years) permanent plots. Most of the species belonging to the community species pool of dry alvar grassland species before clearance were found in permanent plots between 2 and 14 years after the clearance. A large part originated from vegetative spread of already occurring species in the established vegetation in the surroundings. Only a small part of the long-term persistent soil seed bank resulted in the re-establishment of alvar species. There was no significant difference in the traits soil seed bank, seed weight and long-distance dispersal by wind, dung or fur of animals of established and non-established species. Removal of litter and mosses positively affected the re-establishment of alvar species
Territoriaal kapitaal: over de betekenis van erfgoed voor het vestigings- en leefklimaat
Janssen, J. - \ 2012
Vitruvius 6 (2012)21. - ISSN 1874-5008 - p. 8 - 13.
vestiging - stedelijke gebieden - erfgoed - cultureel erfgoed - cultuurgeschiedenis - establishment - urban areas - heritage areas - cultural heritage - cultural history
Het concurrerend vermogen van steden en stedelijke rgio's - hun vermogen om zich als vestigingsplaats te profileren ten opzichte van andere steden en regio's - is in de hedendaagse, geglobaliseerde economie van levensbelang. Als gevolg van de concurrentiestrijd om bedrijven, kenniswerkers en bewoners, neemt de aandacht voor de economische waarde van erfgoed toe. Investeren in gebouwd en landschappelijk erfgoed kan zowel direct als indirect een 'verrijkend' effect hebben op het vestigings- en leefklimaat
Functional analysis of two inhibitor of apoptosis (iap) orthologs from Helicoverpa armigera nucleopolyhedrovirus
Liang, Ch.Y. ; Lange, J. de; Chen, X.W. ; Oers, M.M. van; Vlak, J.M. ; Westenberg, M. - \ 2012
Virus Research 165 (2012)1. - ISSN 0168-1702 - p. 107 - 111.
programmed cell-death - baculovirus gene - insect cells - p35 gene - proteins - lines - identification - establishment - expression - tolerance
Baculoviruses induce apoptotic responses in cultured insect cells, which can severely limit viral replication. To overcome this host response baculoviruses carry anti-apoptotic genes, including members of the p35 and inhibitor of apoptosis (iap) gene families. The baculovirus Helicoverpa armigera nucleopolyhedrovirus (HearNPV) carries two putative apoptosis suppressor genes (iap2 and iap3), which we studied in more detail. IAPs are believed to be functional in the cytoplasm, but surprisingly, when transiently expressed as EGFP fusions, IAP2 was evenly distributed throughout the cell, while IAP3 was mainly found in the nucleus. The latter became evenly distributed in both compartments in HearNPV infected cells. When iap2 was deleted, HearNPV could be propagated in Hz2e5 cells, while an iap3 deletion was lethal. The HearNPV ¿iap3 mutant could be rescued by reinsertion of the HearNPV iap3 gene and by the well-studied anti-apoptotic genes Autographa californica (Ac)MNPV p35 or Orgyia pseudotsugata (Op)MNPV iap3. RNAi analysis showed that HearNPV induced apoptosis in Hz2e5 cells transfected with iap3 dsRNA, while silencing of iap2 did not lead to apoptosis. Finally, IAP3 was able to inhibit actinomycin-D induced apoptosis when transiently expressed in Sf21 cells. These results together indicate that HearNPV IAP3 is a functional apoptosis suppressor, while the function of IAP2 remains elusive.
Flow cytometric evaluation of the effects of 3-bromopyruvate (3BP) and dichloracetate (DCA) on THP-1 cells: a multiparameter analysis
Verhoeven, H.A. ; Griensven, L.J.L.D. van - \ 2012
Journal of Bioenergetics and Biomembranes 44 (2012)1. - ISSN 0145-479X - p. 91 - 99.
induced apoptosis - leukemia-cells - hexokinase ii - liver-cancer - dichloroacetate - line - atp - establishment - transporter - metabolism
Two human leukemia cells K562 and THP-1, the breast cancer lines MCF-7 and ZR-75-1, and the melanoma line MDA-MB-435S were compared by flowcytometry for their behaviour at increasing levels of 3BP. K562 and THP-1 responded to 3BP by membrane depolarization and increased ROS; MCF-7 and ZR-75-1 showed decreased polarization and low ROS increase; MDA-MB-435S had limited depolarization and no ROS increase. THP-1 cells exposed to a range of 3BP concentrations in combination with DCA showed increase of polarization, slight ROS increase, and weakened nuclear integrity. 3BP and DCA show no synergism, but have complementary destructive effects on THP-1 cells. The data led to the conclusion that the THP-1 cells do not carry a functional membrane monocarboxylate transporter (MCT) or that 3BP circumvents MCT binding and can enter these cells independently.
Seed maturation in Arabidopsis is characterised by nuclear size reduction and increased chromatin condensation
Zanten, M. van; Koini, M.A. ; Geyer, R. ; Liu, Y. ; Brambilla, V. ; Bartels, D. ; Koornneef, M. ; Fransz, P. ; Soppe, W.J.J. - \ 2011
Proceedings of the National Academy of Sciences of the United States of America 108 (2011)50. - ISSN 0027-8424 - p. 20219 - 20224.
plant craterostigma-plantagineum - desiccation tolerance - gene-regulation - dormancy - germination - heterochromatin - mutants - establishment - transcription - organization
Most plant species rely on seeds for their dispersal and survival under unfavorable environmental conditions. Seeds are characterized by their low moisture content and significantly reduced metabolic activities. During the maturation phase, seeds accumulate storage reserves and become desiccation-tolerant and dormant. Growth is resumed after release of dormancy and the occurrence of favorable environmental conditions. Here we show that embryonic cotyledon nuclei of Arabidopsis thaliana seeds have a significantly reduced nuclear size, which is established at the beginning of seed maturation. In addition, the chromatin of embryonic cotyledon nuclei from mature seeds is highly condensed. Nuclei regain their size and chromatin condensation level during germination. The reduction in nuclear size is controlled by the seed maturation regulator ABSCISIC ACID-INSENSITIVE 3, and the increase during germination requires two predicted nuclear matrix proteins, LITTLE NUCLEI 1 and LITTLE NUCLEI 2. Our results suggest that the specific properties of nuclei in ripe seeds are an adaptation to desiccation, independent of dormancy. We conclude that the changes in nuclear size and chromatin condensation in seeds are independent, developmentally controlled processes
Selective weed suppression by cover crop residues: effects of seed mass and timing of species’sensitivity
Kruidhof, H.M. ; Gallandt, E.R. ; Haramoto, E.R. ; Bastiaans, L. - \ 2011
Weed Research 51 (2011)2. - ISSN 0043-1737 - p. 177 - 186.
green manure - secale-cereale - growth - management - soil - allelochemicals - rye - phytotoxicity - decomposition - establishment
Laboratory bioassays have shown that large-seeded species better tolerate cover crop residue–mediated stress than small-seeded species. This provides the potential for selective suppression of small-seeded weeds in large-seeded crops. We conducted two field experiments in which seedling emergence of a range of crop and weed species was monitored in soil without cover crop residues and soil with recently incorporated lucerne, winter oilseed rape or winter rye residues. A positive relationship was found between seed mass and tolerance to winter oilseed rape and lucerne residues in both experiments, whereas winter rye residues did not inhibit seedling emergence. Both the gradual reduction in residue-mediated inhibitory potential with time in the first experiment, as well as the sudden increase in lucerne residue–mediated inhibitory potential following a severe rainfall event in the second experiment, illustrated the importance of temporal dynamics. Therefore, we hypothesised that time between residue incorporation and receptor plant emergence could serve as an additional variable for explaining the variation in inhibition of seedling emergence among receptor plant species. Re-analysis of data from two previously published field experiments revealed that seed mass and time of emergence only contributed significantly to explaining variance in receptor plant emergence when both these factors were included in the analysis. Our findings suggest that considering temporal synchrony of receptor species’ sensitivity and potential residue effects in field studies provides a valuable framework for analysing crop residue-mediated effects
Effects of plant-soil feedback on tree seedling growth under arid conditions
Meijer, S.S. ; Holmgren, M. ; Putten, W.H. van der - \ 2011
Journal of Plant Ecology 4 (2011)4. - ISSN 1752-9921 - p. 193 - 200.
arbuscular mycorrhizal fungi - terrestrial ecosystems - semiarid ecosystems - resource pulses - atacama desert - establishment - competition - community - diversity - dynamics
Aims: Plants are able to influence their growing environment by changing biotic and abiotic soil conditions. These soil conditions in turn can influence plant growth conditions, which is called plant–soil feedback. Plant–soil feedback is known to be operative in a wide variety of ecosystems ranging from temperate grasslands to tropical rain forests. However, little is known about how it operates in arid environments. We examined the role of plant–soil feedbacks on tree seedling growth in relation to water availability as occurring in arid ecosystems along the west coast of South America. Methods: In a two-phased greenhouse experiment, we compared plant–soil feedback effects under three water levels (no water, 10% gravimetric moisture and 15% gravimetric moisture). We used sterilized soil inoculated with soil collected from northwest Peru (Prosopis pallida forests) and from two sites in north-central Chile (Prosopis chilensis forest and scrublands without P. chilensis). Important Findings: Plant–soil feedbacks differed between plant species and soil origins, but water availability did not influence the feedback effects. Plant–soil feedbacks differed in direction and strength in the three soil origins studied. Plant–soil feedbacks of plants grown in Peruvian forest soil were negative for leaf biomass and positive for root length. In contrast, feedbacks were neutral for plants growing in Chilean scrubland soil and positive for leaf biomass for those growing in Chilean forest soil. Our results show that under arid conditions, effects of plant–soil feedback depend upon context. Moreover, the results suggest that plant–soil feedback can influence trade-offs between root growth and leaf biomass investment and as such that feedback interactions between plants and soil biota can make plants either more tolerant or vulnerable to droughts. Based on dissecting plant–soil feedbacks into aboveground and belowground tissue responses, we conclude that plant–soil feedback can enhance plant colonization in some arid ecosystems by promoting root growth
Vegetation Re-development After Fen Meadow Restoration by Topsoil Removal and Hay Transfer
Klimkowska, A. ; Kotowski, W. ; Diggelen, R. ; Grootjans, A.P. ; Dzierza, P. ; Brzezinska, K. - \ 2010
Restoration Ecology 18 (2010)6. - ISSN 1061-2971 - p. 924 - 933.
grassland productivity gradient - adhesive seed-dispersal - former arable fields - species richness - plant community - flood-meadow - wet meadows - soil - litter - establishment
We investigated the effects of different restoration treatments on the development of fen meadow communities: (1) depth of topsoil removal, with shallow (circa 20 cm) and deep (circa 40 cm) soil removal applied, (2) transfer of seed-containing hay, and (3) access of large animals. We carried out a full factorial experiment with all combinations of these factors and monitored it for 4 years. We studied the effect of seed availability in the soil seed bank on species abundance in the vegetation and compared it to the effect of species introduction by hay. We observed large differences in species composition between different treatments after 4 years. The combination of hay transfer, deep soil removal, and exclusion of large animals resulted in a community with highest similarity to the target vegetation. We found that the transfer of seeds with hay had a larger effect on species abundance than the soil seed bank. Hay transfer appeared to have important consequences on vegetation development because it speeded up the establishment of the target vegetation.
Strong facilitation in mild environments: the stress gradient hypothesis revisited
Holmgren, M. ; Scheffer, M. - \ 2010
Journal of Ecology 98 (2010)6. - ISSN 0022-0477 - p. 1269 - 1275.
plant-plant interactions - positive interactions - abiotic stress - arid environments - nurse plants - competition - communities - shrubs - establishment - metaanalysis
1. The idea that the role of facilitative interactions increases as environmental conditions become more stressful has become a ruling paradigm in ecology. Here, we review three reasons why positive interactions may actually be more prominent than generally thought under moderately stressful rather than under extreme conditions. 2. First, there is evidence that in some communities the net effect of amelioration of shortage of a limiting resource, such as water under the canopy of nurse plants, may be beneficial under moderate conditions whereas it can be overruled by increased competition for the same resource in very harsh environments. 3. Secondly, we show that even in situations where the relative role of facilitation increases monotonically with stress, the absolute effect should as a rule be largest at intermediately stressful conditions. This is because under the harshest conditions, facilitative amelioration of conditions is insufficient to allow growth altogether. Therefore, while facilitation will expand the range of conditions where an organism may occur, the largest absolute effects on biomass will always occur under less stressful conditions. 4. A third reason why facilitation may be more important under moderate conditions than previously thought is that in any ecosystem, the suite of organisms is adapted to local conditions. This implies that even under conditions that appear benign, facilitation may play an unexpectedly large role as organisms are simply more sensitive than those found under harsher overall conditions. 5. Synthesis. We argue that while facilitation will extend the range of conditions where an organism can occur, it should also boost performance of the species well into the more moderate range of conditions. Broadening our search image for facilitative effects towards milder environments will reveal wider than expected prevalence of positive interactions and their effects on stability and diversity in nature.
Mixed mating system in the fern Asplenium scolopendrium: implication for colonization potential
Bremer, P. ; Wubs, E.R.J. ; Groot, G.A. de; During, H.J. ; Vogel, J.C. ; Grundmann, M. ; Schneider, H. - \ 2010
Annals of Botany 106 (2010)4. - ISSN 0305-7364 - p. 583 - 590.
long-distance dispersal - reproductive-biology - genetic diversity - inbreeding depression - population-structure - blechnum-spicant - breeding-system - pteridophyta - establishment - success
Background and Aims Human-mediated environmental change is increasing selection pressure for the capacity in plants to colonize new areas. Habitat fragmentation combined with climate change, in general, forces species to colonize areas over longer distances. Mating systems and genetic load are important determinants of the establishment and long-term survival of new populations. Here, the mating system of Asplenium scolopendrium, a diploid homosporous fern species, is examined in relation to colonization processes. Methods A common environment experiment was conducted with 13 pairs of sporophytes, each from a different site. Together they constitute at least nine distinct genotypes, representing an estimated approx. 95 % of the non-private intraspecific genetic variation in Europe. Sporophyte production was recorded for gametophytes derived from each parent sporophyte. Gametophytes were grown in vitro in three different ways: (I) in isolation, (II) with a gametophyte from a different sporophyte within the same site or (III) with a partner from a different site. Key Results Sporophyte production was highest in among-site crosses (III), intermediate in within-site crosses (II) and was lowest in isolated gametophytes (I), strongly indicating inbreeding depression. However, intragametophytic selfing was observed in most of the genotypes tested (eight out of nine). Conclusions The results imply a mixed mating system in A. scolopendrium, with outcrossing when possible and occasional selfing when needed. Occasional intragametophytic selfing facilitates the successful colonization of new sites from a single spore. The resulting sporophyte, which will be completely homozygous, will shed large amounts of spores over time. Each year this creates a bed of gametophytes in the vicinity of the parent. Any unrelated spore which arrives is then selectively favoured to reproduce and contribute its genes to the new population. Thus, while selfing facilitates initial colonization success, inbreeding depression promotes genetically diverse populations through outcrossing. The results provide further evidence against the overly simple dichotomous distinction of fern species as either selfing or outcrossing.
Potential of endozoochorous seed dispersal by sheep in calcareous grasslands: correlations with seed traits.
Kuiters, A.T. ; Huiskes, H.P.J. - \ 2010
Applied Vegetation Science 13 (2010)2. - ISSN 1402-2001 - p. 163 - 172.
vascular plants - cattle dung - species richness - large herbivores - establishment - restoration - landscape - impact - communities - migration
Questions: What is the potential of sheep to serve as seed dispersers via ingestion and defecation in calcareous grasslands? Is the presence of viable seeds from dung correlated with specific seed traits? Location: Calcareous grasslands, South Limburg, the Netherlands/Belgium. Methods: Dung samples (n=24) from sheep were collected between September 2006 and November 2007 from five sites with Mesobromion plant communities, and communities of Nardo-Galion saxatilis. Germinability and identity of seeds in the dung samples were ascertained from germination of seedlings under glasshouse conditions. Seed traits of species with viable seeds in dung were compared with those present in the local species pool. Results: Seventy-two plant species from 23 plant families had viable seeds in sheep dung. The plant families encountered most frequently were Gramineae and Compositae. The most abundant and frequently recorded plant species in dung samples was Urtica dioica, accounting for >80% of the total number of seeds. Mean seed density in sheep dung was 0.8 seeds g-1 dry matter. Seeds with low seed mass and a high seed longevity index were over-represented in dung. Viable seeds >2.5 mg were infrequent in the dung samples. Conclusions: We conclude that sheep are potentially important dispersers of plant species in Dutch calcareous grasslands. Although smaller seeds were relatively abundant in sheep dung, it cannot be excluded that this was mainly caused by differences in seed abundance.
Suitability of PER.C6 (R) cells to generate epidemic and pandemic influenza vaccine strains by reverse genetics
Koudstaal, W. ; Hartgroves, L. ; Havenga, M. ; Legastelois, I. ; Ophorst, C. ; Sieuwerts, M. ; Zuijdgeest, D. ; Vogels, R. ; Custers, J. ; Boer-Luijtze, E.A. de; Leeuw, O.S. de; Cornelissen, A.H.M. ; Goudsmit, J. ; Barclay, W. - \ 2009
Vaccine 27 (2009)19. - ISSN 0264-410X - p. 2588 - 2593.
a virus generation - rna-polymerase - system - establishment - rescue - dna
Reverse genetics, the generation of influenza viruses from cDNA. presents a rapid method for creating vaccine strains. The technique necessitates the use of cultured cells. Due to technical and regulatory requirements, the choice of cell lines for production of human influenza vaccines is limited. PER.C6 (R) cells, among the most extensively characterized and documented cells, support growth of all influenza Viruses tested to date, and can be grown to high densities in large bioreactors in the absence of serum or micro carriers. Here, the suitability of these cells for the generation of influenza Viruses by reverse genetics was investigated. A range of viruses reflective of vaccine strains was rescued exclusively using PER.C6 cells by Various transfection methods, including an animal component-free procedure. Furthermore, a whole inactivated vaccine carrying the HA and NA segments of A/HK/156/97 (H5N1) that was both rescued from and propagated oil PER.C6 cells, conferred protection in a mouse model. Thus PER.C6 cells provide an attractive platform for generation of influenza vaccine strains via reverse genetics.
Transgenes in Mexican maize: molecular evidence and methodological considerations for GMO detection in landrace populations
Pineyro-Nelson, A. ; Heerwaarden, J. van; Perales, H.R. ; Serratos-Hernandez, J.A. ; Rangel, A. ; Hufford, M.B. ; Gepts, P. ; Garay-Arroyo, A. ; Rivera-Bustamante, R. ; Alvarez-Buylla, E.R. - \ 2009
Molecular Ecology 18 (2009)4. - ISSN 0962-1083 - p. 750 - 761.
bentgrass agrostis-stolonifera - biodiversity communications - (trans)gene flow - crop origin - gene flow - diversity - pollen - establishment - evolution - centers
A possible consequence of planting genetically modified organisms (GMOs) in centres of crop origin is unintended gene flow into traditional landraces. In 2001, a study reported the presence of the transgenic 35S promoter in maize landraces sampled in 2000 from the Sierra Juarez of Oaxaca, Mexico. Analysis of a large sample taken from the same region in 2003 and 2004 could not confirm the existence of transgenes, thereby casting doubt on the earlier results. These two studies were based on different sampling and analytical procedures and are thus hard to compare. Here, we present new molecular data for this region that confirm the presence of transgenes in three of 23 localities sampled in 2001. Transgene sequences were not detected in samples taken in 2002 from nine localities, while directed samples taken in 2004 from two of the positive 2001 localities were again found to contain transgenic sequences. These findings suggest the persistence or re-introduction of transgenes up until 2004 in this area. We address variability in recombinant sequence detection by analyzing the consistency of current molecular assays. We also present theoretical results on the limitations of estimating the probability of transgene detection in samples taken from landraces. The inclusion of a limited number of female gametes and, more importantly, aggregated transgene distributions may significantly lower detection probabilities. Our analytical and sampling considerations help explain discrepancies among different detection efforts, including the one presented here, and provide considerations for the establishment of monitoring protocols to detect the presence of transgenes among structured populations of landraces
Continuous growth of the giant grass Zizaniopsis bonariensis in subtropical wetlands
Finkler Ferreira, T. ; Nes, E.H. van; Motta Marques, D. da - \ 2009
Freshwater Biology 54 (2009)2. - ISSN 0046-5070 - p. 321 - 330.
aboveground primary production - typha-latifolia - emergent macrophytes - population-dynamics - modeling approach - germination - establishment - ecosystems - strategies - patterns
1. Zizaniopsis bonariensis (giant grass) is an emergent macrophyte species endemic to subtropical wetlands in Brazil, Argentina, Paraguay and Uruguay. In this study, we show the effects of its continuous clonal reproduction and its 'phalanx' growth strategy in the Taim Wetland (southern Brazil). 2. The continuous clonal growth of this 3-m high grass gave rise to the emergence of 11.7 new shoots m-2 per month and a high total above ground production (2870 g dry weight m-2 year-1). The biomass of the new shoots emerging every month formed a wave of growth, moderated by only weak seasonal variation. 3. We show its phalanx growth strategy by analysing the variations in population density and shoot height within a transect through the stand canopy. The inverse relation between density and height from the border to the interior indicates self-regulation of biomass. 4. The plants modified their environment, enhancing resistance to drought within the stand and thus facilitating their dominance. This positive feedback suggests that the dominance of the plant might constitute an alternative state in subtropical wetlands
Local positive feedback and the persistence and recovery of fringe Avicennia marina (Forssk.) Vierh. mangroves
Huisman, T.J. ; Langevelde, F. van; Boer, W.F. de - \ 2009
Wetlands Ecology and Management 17 (2009)6. - ISSN 0923-4861 - p. 601 - 611.
early-life history - early growth - ecosystems - restoration - australia - establishment - regeneration - propagules - patterns - forests
While mangrove restoration efforts are reasonably successful, failure often occurs in high wave energy situations. Due to differences in wave energy, seedling mortality rates vary strongly with position on the intertidal flat between high water spring and high water neap elevations. However, a local positive feedback can be present between the pneumatophores of adult mangroves and the survival of mangrove seedlings to trigger recovery. In this study, a mangrove population of Avicennia marina is modelled to determine the effects of seedling mortality and local positive feedback on mangrove recovery. The model uses life history data and dispersal to simulate population dynamics. The mangrove range limits are determined by high water spring and high water neap levels. The results indicate that within these limits mangrove populations with life-history parameter values as derived from literature are indeed capable of fast growth under conditions with low seedling mortality. Local positive feedback has then a small positive influence on population recovery after mangrove loss. If, however, mortality rates increase, such as in high wave energy situations, the importance of a positive feedback increases. The model shows that a positive feedback may, given high seedling mortality rates, be an important factor for mangrove recovery. While a positive feedback may enable mangrove persistence in unfavourable conditions, destruction of adult mangroves can remove the positive feedback, which would render the system uninhabitable and practically prohibits reforestation of such areas. The model results and the presence of positive feedbacks and their importance for population dynamics in harsh conditions indicate that investigating and understanding possible feedbacks could be crucial for successful restoration efforts
Water and nutrients alter herbaceous competitive effects on tree seedlings in a semi-arid savanna
Waal, C. van der; Kroon, H. de; Boer, W.F. de; Heitkonig, I.M.A. ; Skidmore, A.K. ; Knegt, H.J. de; Langevelde, F. van; Wieren, S.E. van; Grant, R.C. ; Page, B.R. ; Slotow, R. ; Kohi, E. ; Mwakiwa, E. ; Prins, H.H.T. - \ 2009
Journal of Ecology 97 (2009)3. - ISSN 0022-0477 - p. 430 - 439.
african savannas - colophospermum-mopane - grass competition - soil-moisture - south-africa - woody cover - fire - establishment - vegetation - acacia
1. Globally, both climatic patterns and nitrogen deposition rates show directional changes over time. It is uncertain how woody seedlings, which coexist with herbaceous plants in savannas, respond to concurrent changes in water and nutrient availability. 2. We investigated competition effects between herbaceous vegetation and tree seedlings (Colophospermum mopane) under changed water and nutrient (fertilized) conditions in a garden experiment situated in a semi-arid savanna. 3. Herbaceous competition significantly suppressed woody seedling growth. The effect of herbaceous competition on woody seedling growth remained constant with both increasing water and nutrient availability. However, during a wet-season drought, herbaceous competition apparently caused premature leaf senescence in non-irrigated treatments. Fertilization exacerbated negative competition effects during the drought, while irrigation prevented leaf loss of tree seedlings in spite of herbaceous competition and fertilization. 4. Based on a conceptual model, we propose that the vigorous response of herbaceous plants to increased nutrient availability leads to faster depletion of soil water, which increasingly causes water stress in woody seedlings if the interval between watering events is prolonged, e.g. during wet-season droughts. 5. Synthesis. Our data support the notion that changes in drought frequency are of greater importance to woody recruitment success than changes in annual rainfall amount. Based on the water and nutrient interactions observed in our experiment, we suggest that the effect of increased nitrogen deposition on woody seedling recruitment is contingent on water availability.
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