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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    Mechanisms of vegetative propagation in bulbs : a molecular approach
    Moreno-Pachón, Natalia - \ 2017
    Wageningen University. Promotor(en): R.G.H. Immink, co-promotor(en): H.W.M. Hilhorst. - Wageningen : Wageningen University - ISBN 9789463437011 - 178
    ornamental bulbs - tulipa - lilium - vegetative propagation - flowering date - gene regulation - genes - transcriptomes - dna sequencing - regeneration - shoot apices - bloembollen - tulipa - lilium - vegetatieve vermeerdering - bloeidatum - genregulatie - genen - transcriptomen - dna-sequencing - verjonging - scheuttoppen

    Vegetative propagation is very important for the survival of species with long juvenile and adult vegetative phases, as it is the case for bulbous plants. Bulbous plants are ornamental geophytes with a bulb as an underground storage organ. Among flower bulbs, tulip and lily are the two commercially leading plants in The Netherlands. Tulip propagates vegetatively via axillary bud outgrowth, while lily propagates via adventitious bulblet formation. The vegetative propagation rate in tulip is very low due to the limited amount of axillary buds that will grow successfully. Moreover, tulip is very recalcitrant to in vitro regeneration. On the other hand, lily propagates efficiently via adventitious bulblet formation, either naturally from the underground portion of the stem of the apical bud, or artificially from detached bulb scales.

    This thesis study aimed to understand how axillary bud outgrowth is controlled in tulip bulbs and how regeneration capacity is established in lily bulb scales. As a first step towards these goals, the state of the art of the molecular control of sexual and vegetative reproduction was reviewed for model species. Moreover, two approaches, “bottom-up” and “top-down”, to transfer the knowledge from model to non-model species were described (Chapter 2). In short, the “bottom-up” approach usually goes from individual genes to systems, assuming conservation of molecular pathways and using sequence homology searches to identify candidate genes. ”Top-down” methodologies go from systems to genes, and are based on large scale transcriptome profiling via e.g. microarrays or RNA sequencing, followed by the identification of associations between phenotypes, genes, and gene expression patterns and levels.

    Next (Chapter 3), two sets of high quality transcriptomes, one for tulip and one for lily were generated from a collection of several tissues using the Illumina HiSeq 2000 platform. Several assembly filtering parameters were applied, to highlight the limitations of stringent but routinely used filtering in de novo transcriptome assembly. The final created transcriptomes were made publicly available via a user friendly Transcriptome browser (http://www.bioinformatics.nl/bulbs/db/species/index) and their usefulness was exemplified by a search for all potential transcription factors in lily and tulip, with special focus on the TCP transcription factor family.

    One TCP member was of special interest because it has proven to integrate several pathways that control axillary bud outgrowth in a wide range of species. It is called TEOSINTE BRANCHED 1 (TB1) in monocots and BRNACHED 1 (BRC1) in dicots. A Tulipa gesneriana TB1 transcript was identified from the generated transcriptome and subsequently, tulip axillary bud outgrowth was studied through a “bottom-up” approach (Chapter 4). The degree of axillary bud outgrowth in tulip determines the success of their vegetative propagation. However the number of axillary meristems in one bulb is low –six on average– and not all of them seem to have the same growth capacity. The combination of physiological and targeted molecular experiments indicated that the first two inner located buds do not seem to experience dormancy (assessed by weight increase and TgTB1expression) at any point of the growth cycle, while mid-located buds enter dormancy by the end of the growing season. Moreover it was shown that TgTB1 expression in tulip bulbs can be modulated by sucrose, cytokinin and strigolactone, just as it has been reported for other species. However, the limited growth of mid-located buds even when their TgTB1 expression was naturally or artificially downregulated, pointed at other factors, probably physical, inhibiting their growth.

    Next, the remarkable regeneration capacity of lily by initiating de novo shoot meristems from excised bulb scales without the addition of exogenous hormones or growth regulators was studied using a “top-down” approach (Chapter 5). An extensive and comprehensive transcriptome set was generated from lily bulb scales in a time-series using two cultivars and two explant types, all differing in regeneration capacity. This set up provided first insight in the key molecular process underlying pro-meristem induction and meristem initiation in lily. We found that wounding activates a very fast regeneration response, probably mediated by APETALA2/ETHYLENE RESPONSIVE FACTORS (AP2/ERF,) such as LoERF115 and WOUND INDUCED DEDIFFERENTIATION 2 (LoWIND2), which in turn might mediate polar auxin re-distribution, cell proliferation and de-differentiation. Moreover, the timing and level of induction of shoot meristem regulators, such as ENHANCER OF SHOOT REGENERATION 2 (LoESR2) and SHOOT MERISTEMLESS (LoSTM) correlated with the regeneration capacity of the scale.

    Regardless the regeneration capacity of the different explants e.g. cultivar or position within the scale, regeneration occurs at the proximal-adaxial side of the bulb scale, right on top of the excision line. Thus the possible cellular and physiological factors granting lily bulb scales their competence to regenerate was investigated (Chapter 6). We found that the adaxial parenchyma tissue seems to be more competent than the abaxial tissue, partially because of higher number of secondary veins and larger cell population than the abaxial parenchyma region. It was proposed that upon explant excision, the polar auxin transport is disrupted, creating an auxin maximum at the excision line, which might create a gradient of cell divisions favouring the adaxial parenchyma tissue. The direction of this cell division gradient proved to be negatively affected by the absence of the adaxial epidermis. Moreover, explants without epidermis reduced dramatically their regeneration capacity, and lost the typical proximal-adaxial orientation of regeneration. Thus, a better understanding of the composition and physiology of the epidermis in lily bulb scales is essential to identify the regeneration stimulating signals originating from this tissue layer in Lilium sp.

    Finally in Chapter 7, integration of all the results was done and I addressed how this may contributes to the fundamental and applied understanding of vegetative propagation in bulbous plants. Also, some challenges are discussed, for example, the complexity in the architecture of tulip bulbs and how this influences ways for improving its rate of axillary bud outgrowth. The challenge to prove the findings of this thesis through functional analysis is also discussed and the possibility of using transient virus-induced gene silencing is highlighted. Moreover, the potential of lily bulb scales as a model system to study some aspects of de novo regeneration, as well as to study the recalcitrance of in vitro propagation is highlighted, supporting the idea that more “omics” data and biotechnological tools for bulbous plant research are necessary.

    Applied and fundamental aspects of BABY BOOM-mediated regeneration
    Heidmann, I.A. - \ 2015
    Wageningen University. Promotor(en): Gerco Angenent, co-promotor(en): Kim Boutilier. - Wageningen : Wageningen University - ISBN 9789462574663 - 180
    nicotiana tabacum - capsicum annuum - verjonging - transcriptiefactoren - somatische embryogenese - auxinen - moleculaire biologie - nicotiana tabacum - capsicum annuum - regeneration - transcription factors - somatic embryogenesis - auxins - molecular biology

    Keywords: Somatic embryogenesis, Transcription factor, AINTEGUMENTA-LIKE, BABY BOOM, BBM, Sweet Pepper Transformation

    Title: Applied and Fundamental Aspects of BBM-mediated Regeneration

    Author: Iris Heidmann

    Catergories: Plant regeneration, Plant transformation, transcription factor, somatic embryogenesis

    Plant regeneration from tissues or single cells is essential for plant propagation. Efficient regeneration can be archieved through somatic embryogenesis using the plant growth regulator auxin or overexpression of specific transcription factors, but the underlying mechanisms are poorly understood. The potency of the BABY BOOM (BBM) AINTEGUMENTA-LIKE transcription factor to induce somatic embryogenesis in crop (sweet pepper) and model species (tobacco) was investigated. It was found that the introduction of BBM into sweet pepper, which is recalcitrant for transformation, enhanced the regeneration of transgenic plants. Exogenous cytokinin was necessary to induce somatic embryogenesis in both tobacco and sweet pepper. The mechanism underlying BBM-mediated somatic embryogenesis was studied in Arabidopsis by identifying BBM target genes (ChIPSeq). Genes controlling zygotic embryo identity and maturation (LAFL), as well as auxin biosynthesis (TAA1, YUCCA) and transport (PIN) are BBM targets. Mutant analysis and chemical inhibition studies showed that these genes play positive roles in BBM-induced somatic embryogenesis.

    Forest management and regeneration of tree species in the Eastern Amazon
    Schwartz, G. - \ 2013
    Wageningen University. Promotor(en): Frits Mohren; Bas Arts, co-promotor(en): Marielos Pena Claros; J.C.A. Lopes. - S.l. : s.n. - ISBN 9789461734662 - 132
    bosbedrijfsvoering - bomen - soorten - verjonging - houtkap - houtteelt - amazonia - forest management - trees - species - regeneration - logging - silviculture - amazonia

    Forest management for timber production applied in the Brazilian Amazon follows a polycyclic silvicultural system where harvesting is done through reduced-impact logging (RIL). In this study the short- and medium-term effects of RIL on the regeneration of commercial tree species were assessed in the Tapajós National Forest, Eastern Amazon, Brazil. Besides, post-harvesting silvicultural techniques such as enrichment planting using commercial tree species and tending naturally established individuals in gaps created by RIL were tested in Jari Valley, Eastern Amazon, Brazil in order to improve forest management for ensuring sustainable timber production. Finally the profitability of the tested post-harvesting silvicultural treatments was evaluated. Results showed that RIL did not have a destructive effect on the regeneration of the investigated species. In the short-term RIL caused unevenly spatially distributed disturbances over the forest, which tended to increase recruitment and growth rates of seedlings and saplings in the medium-term. The silvicultural techniques proved to be efficient to decrease mortality and increase growth rates of commercial tree species but are not profitable under the current timber prices and harvesting operation costs in the Brazilian Amazon. Although not profitable, enrichment planting in logging gaps showed to be an important tool for conserving rare species.

    Ontwikkeling van soortensamenstelling en kwaliteit van gemengde natuurlijke bosverjonging
    Oosterbaan, A. ; Berg, C.A. van den - \ 2012
    Vakblad Natuur Bos Landschap 2012 (2012)mei. - ISSN 1572-7610 - p. 14 - 17.
    bosecologie - verjonging - bosverrijking - zandgronden - forest ecology - regeneration - improvement planting - sandy soils
    Bij gemengde verjongingen is het soms een probleem om gewenste boomsoort(en) in de menging te houden. Om een gewenste soort voldoende kans te bieden, moet wellicht in een vroeg stadium ingegrepen worden. In 2010 is een onderzoek uitgevoerd naar de ontwikkeling in de eerste 15-25 jaar van de belangrijkste gemengde natuurlijke verjongingstypen in bossen op hoge zandgronden. Hierbij is ook gekeken naar de noodzaak om in deze leeftijdsfase beheermaatregelen uit te voeren.
    Verjongingsbeheer bomenbestand Park Randenbroek en Vosheuvel
    Oosterbaan, A. ; Berg, C.A. van den; Kopinga, J. - \ 2010
    Wageningen : Alterra, Wageningen-UR (Alterra-rapport 2100) - 46
    bosplantages - achteruitgang, bossen - verjonging - openbare parken - gemeenten - utrecht - forest plantations - forest decline - regeneration - public parks - municipalities - utrecht
    Advies voor het verjongingsbeheer van het bomenbestand in Park Randenbroek en de oude boskern van Vosheuvel in de periode 2010-2020
    Natuurlijke ontwikkelingen in het Amsterdamse Bos : een studie naar de bosontwikkeling in de Natuurboszone en de Parkboszone
    Verkaik, E. ; Koop, H.G.J.M. ; Clerkx, A.P.P.M. - \ 2010
    Wageningen : Alterra (Alterra-rapport 2102) - 48
    bossen - bosbouw in steden - beschermde bossen - bosstructuur - bosbedrijfsvoering - stedelijke gebieden - natuurontwikkeling - verjonging - botanische samenstelling - amsterdam - noord-holland - forests - urban forestry - reserved forests - forest structure - forest management - urban areas - nature development - regeneration - botanical composition - amsterdam - noord-holland
    De bosontwikkeling in de Noordboszone en Parkboszone van het Amsterdamse bos zijn onderling vergeleken op openheid van het bos, mate van ontmenging van de boomlaag en hoeveelheid dood hout. Beide beheersvormen verschillen onderling in openheid, mate van verjonging, belevingswaarde en boomsoortensamenstelling nu en in de toekomst. De afwisseling van beide beheersvormen geeft een extra meerwaarde aan het bos en zou naast elkaar gehandhaafd moeten worden. Ontmenging of veresdoorning door nietsdoen-beheer treedt nauwelijks op. De waterkwaliteit moet gewaarborgd blijven door afvoeren van blad- en takafval, waarbij voorkomen moet worden dat de oevers worden opgehoogd.
    Sterfte en verjonging in bosreservaten
    Verkaik, E. - \ 2010
    Wageningen : Alterra (Alterra-rapport 2086) - 40
    beschermde bossen - bosecologie - verjonging - nederland - mortaliteit - reserved forests - forest ecology - regeneration - netherlands - mortality
    In dit rapport wordt de sterfte en verjonging die plaatsvindt in Nederlandse bosreservaten op een rij gezet. Hiervoor is gebruik gemaakt van de gegevens die verzameld zijn in steekproefcirkels. Het gemiddelde sterftepercentage in de reservaten was 1.7% en de bomen in de reservaten gingen vooral dood door concurrentie tussen de bomen onderling. De sterftepercentages verschilden duidelijk tussen bostypen. Ook de hoeveelheid verjonging verschilde sterk tussen de verschillende bostypen. Gemiddeld werden er 1336 ‘jonge bomen en struiken’ per hectare gevonden (bomen met een diameter kleiner dan 5cm maar hoogte groter dan 50cm). Van de aanwezige verjonging groeide per jaar slechts een klein deel, zo’n 1.5-2.5%, op tot een boom of struik met een diameter groter dan 5 cm.
    Konijn en jeneverbes: een moeizame relatie
    Hommel, P.W.F.M. ; Huiskes, R. - \ 2009
    Nature Today 2009 (2009)7-11-2009.
    flora - vegetatietypen - juniperus - verjonging - abiotische beschadigingen - konijnen - heidegebieden - natuurgebieden - flora - vegetation types - juniperus - regeneration - abiotic injuries - rabbits - heathlands - natural areas
    Het gaat goed met de konijnen in onze heide- en stuifzandgebieden; na de dramatische achteruitgang van enkele jaren geleden zijn de aantallen het afgelopen jaar weer duidelijk toegenomen. Dat is goed voor de natuur, maar het heeft ook consequenties voor het voorkomen van sommige plantensoorten. Door konijnenvraat krijgt bijvoorbeeld de jeneverbes amper de kans zich te verjongen, zo constateren onderzoekers van Alterra
    Tree recruitment in West African dry woodlands : the interactive effects of climate, soil, fire and grazing
    Biaou, S.S.H. - \ 2009
    Wageningen University. Promotor(en): Frits Mohren, co-promotor(en): Frank Sterck; Milena Holmgren Urba. - [S.l.] : S.n. - ISBN 9789085853183 - 182
    bosgebieden - verjonging - begrazing - bodem - brandgevolgen - soortenrijkdom - bodemvruchtbaarheid - bossen - waterstress - populatie-aanwas - west-afrika - benin - woodlands - regeneration - grazing - soil - fire effects - species richness - soil fertility - forests - water stress - recruitment - west africa - benin
    Growth patterns, competition and coexistence in gap-phase regeneration under close-to-nature silviculture
    Dekker, M. - \ 2008
    Wageningen University. Promotor(en): Frits Mohren, co-promotor(en): Jan den Ouden. - [S.l.] : S.n. - ISBN 9789085049746 - 169
    houtteelt - verjonging - groei - natuurlijke verjonging - bosbedrijfsvoering - bossen - bosbouw - bosbeleid - gaten in het kroondak - europa - silviculture - regeneration - growth - natural regeneration - forest management - forests - forestry - forest policy - canopy gaps - europe
    The dominant European forest policy objective is to create multifunctional, mixed-species and uneven-aged forests. This objective includes the nature‐oriented conversion of monospecific plantations. To reach this objective, close-to-nature silviculture is applied. This generally entails natural regeneration in canopy gaps. In the Netherlands, experience with gap-phase regeneration is limited, making it difficult to asses the effect of close-to-nature management on forest development. In this thesis, this problem is addressed by investigating species coexistence between the four dominant species that occur in naturally regenerated canopy gaps in Douglas fir forest in the Netherlands. These species are Silver birch (Betula pendula Roth.), Japanese larch (Larix kaempferi Carr.), Scots pine (Pinus sylvestris L.) and Douglas fir (Pseudotsuga menziesii Mirb. Franco).
    During gap‐phase regeneration, saplings undergo self‐thinning. This affects species composition of the regeneration unit. Important factors in self‐thinning are species‐specific morphological growth patterns, emergent stand characteristics, the effect of stand characteristics on competitive relationships, and the effect of light availability on growth and mortality.
    Growth patterns differed between species and resulted in differences in the achieved height per unit biomass. Differences in mass‐based heights subsequently caused a vertical stratification in the regeneration unit which, in turn, affected the interspecific competition for light. However, results demonstrated a competitive response rather than a competitive effect. Surrounding saplings formed a functionally equivalent neighborhood, and target individuals responded mainly to their position in the canopy.
    Canopy position affected the radial growth of saplings. Mortality probabilities depended on radial growth, but did not differ between species despite a wide range in light demand. Scots pine did not show a relation between growth and mortality, even though it is highly responsive to light.
    Under continued autogenic development, a low-density top stratum of Silver birch and Japanese larch will develop, overtopping a declining number of Scots pine and a large number of increasingly dominant Douglas fir. This implies that Scots pine will be outcompeted by the other species, and Douglas fir will gain dominance in the future. Forest conversion by natural regeneration will therefore not lead to the desired mixed-species composition, but stands will eventually revert back to Douglas fir forest. Maintaining a diverse forest thus means the need for interventions in the early developmental stage.

    De spontane ontwikkeling van een jong bos op zeeklei (bosreservaat Hollandse Hout, Oostelijk Flevoland) : een analyse voorafgaand aan de aantakking van de Hollandse Hout op de Oostvaardersplassen
    Bijlsma, R.J. ; Verkaik, E. - \ 2008
    Wageningen : Alterra (Alterra-rapport 1615) - 49
    bossen - natuurlijke verjonging - verjonging - vegetatie - bosecologie - begrazing - plantensuccessie - zware kleigronden - zuidelijk flevoland - forests - natural regeneration - regeneration - vegetation - forest ecology - grazing - plant succession - clay soils - zuidelijk flevoland
    De spontane ontwikkeling in bosstructuur en vegetatie van bosreservaat Hollandse Hout bij Lelystad tussen 1995 en 2007 wordt besproken in het licht van de verwachte aantakking van de Hollandse Hout op de Oostvaardersplassen. De belangrijkste boomsoorten zijn es, esdoorn, eik en populier waarvan verjonging en sterfte zijn bepaald. De verjonging van es in relatie tot lichtbeschikbaarheid en het optreden van brandnetels en slakken wordt apart behandeld. De ontwikkeling van de bosflora wordt vergeleken met die in andere kleibossen in de polder en blijkt afhankelijk van paden en een heterogene bosstructuur. Tot slot worden prognoses voor de bosontwikkeling bij hoge graasdruk besproken, zoals verwacht na aantakking
    Bosgaten in het Voosterbos : een evaluatie van bosgaten in de periode 2000 - 2006 en voorstel voor nieuwe ingrepen
    Bremer, P. - \ 2007
    's-Gravenland : Natuurmonumenten - 40
    bossen - bosbeheer - opstandsdichtheid - verjonging - bosecologie - noordoostpolder - natuurgebieden - forests - forest administration - stand density - regeneration - forest ecology - noordoostpolder - natural areas
    In het Voorsterbos is na de overdracht van Staatsbosbeheer naar Natuurmonumenten een andere wind gaan waaien, waarbij een zo natuurlijk mogelijk beheer voorop staat. Een van de beheersvormen die daarbij aan de orde is betreft de mozaiekmethode. In de winter van 1999/2000 zijn de eerste gaten gekapt in een Beuk-opstand. In de periode 2000 - 2006 zijn in totaal 54 bosgaten gekapt. Dit rapport had als centrale vraagstelling: wat heeft het kappen van bosgaten opgeleverd voor de bosverjonging, flora en vegetatie
    Ethiopian church forests : opportunities and challenges for restoration
    Wassie Eshete, A. - \ 2007
    Wageningen University. Promotor(en): Frans Bongers, co-promotor(en): D. Teketay; Frank Sterck. - [S.l.] : S.n. - ISBN 9789085047681 - 204
    bossen - bosecologie - verjonging - kerken - vegetatie - ethiopië - forests - forest ecology - regeneration - churches - vegetation - ethiopia
    In Northern Ethiopia almost all dry Afromontane forests have been converted to open agricultural lands. Only small isolated fragments remain around churches ("church forests"), but these are many. This study analyses forest community structure and composition of the church forests, investigates major bottlenecks for regeneration of woody species, and explores opportunities and challenges for restoration. In this thesis, the following major questions are addressed: 1. How do forest structure, species composition and biodiversity vary
    across church forests and what are the major factors driving such variations?
    Factors considered are altitude, forest size and human influence. 2. What are the major bottlenecks in the regeneration of woody plants in
    church forests? These bottlenecks are studied for one to seven church forests and a
    major focus is given to the effects of soil seed bank and post-dispersal seed
    predation on seedling establishment, and of livestock grazing, microsite gradients
    and management interventions on seedling establishment, seedling survival and
    growth. The species and structural composition of 28 forests located at different altitudes (range 1816 to 3111 masl) and of various sizes (range 1.6 to 100 ha) was assessed, in relation to altitude, forest area, livestock grazing intensity and wood harvest intensity. A total of 168 woody species (100 tree species, 51 shrubs and 17 lianas) representing 69 families were recorded in the 28 church forests studied. Out of these species, 160 were indigenous and only eight were exotic (2 shrub and 6 tree species) representing 6 families. These forests accommodate many species represented by single individuals (rare species) and also many species found only in single plots (unique), which makes church forests priority of conservation efforts. Forests differed strongly in species number (15 to 78), basal area (4.8 to 111.5 m2/ha), density (> 5 cm dbh: 267 to 1553/ha; >cm diameter: 619 to 2421/ha and; seedlings: o to 5263/ha). Altitude is the main factor determining species composition of these forests. Our results showed that altitudinal gradient is the main determinant of differences in species composition among these forests. Maximum similarity in species composition was found with minimum altitude difference between forests. Geographical distance had only a weak effect on similarity. Therefore their vas altitudinal distribution gives these forests the opportunity to hold most of the biodiversity resources of the area. This can be confirmed by the number of specie: we found in our 28 church forests (168) which is more than the expected number 0 species (125 woody species) listed in the study area by South Gondar Zona Department of Agriculture. Structural composition of these forests, on the other hand, is determined by human influence. In the understorey the interaction effect of altitude with human influence (particularly cattle interference) determines the species composition. Not only the species composition but also the number of seedlings were severely affected by cattle interference and few, if any, seedlings were found in some of the forests. In the long run this would probably lead to a human effect on overstorey composition of these forests as well. Forest area did not show a significant effect. This implies that although large sized forests are a necessary element of successful reproduction of woody species, small patches and appropriate matrix management could be useful complements for biodiversity conservation. For many tree species regeneration in most of these forests is very limited. Possible reasons for this limitation are addressed in field experiments. Soil seed bank analysis on seven of these forests showed that these forests accumulate large quantities of persistent seeds of herbaceous species in the soil, but only five (6%) of the 91 woody species recorded in the standing vegetation of the seven forests were represented in their soil seed banks. Most of the tree species do not accumulate seeds in the soil. In order to investigate the long term behavior of seeds in forest soil, we assessed seed viability of five tree species in four sites of one forest after being buried 6, 12, or 18 months. Seed viability decreased sharply with burial time in soil for all species except for seeds of Juniperus, which still had 91% of viability after 18 months. Species significantly affect "the viability of the seeds after 18 months of burial. The quick decline of seed viability in forest soil indicates that the study species do not have a persistent soil seed bank. The fact that most of the dominant tree species do not accumulate seeds and maintain viability in the soil suggests that their regeneration from seeds would be prevented by removal of mature individuals in the standing vegetation. The experiment of post-dispersal seed predation on seeds of six tree species in one forest showed that 92% of the seeds were predated within 3.5 months. Therefore lack of persistent soil seed bank aggravated by intense seed predation undermines seed availability for regeneration in church forests. For four selected tree species in two forests this study showed that livestock grazing is one of the main bottlenecks hampering seedling establishment, seedling survival and seedling growth. Almost none of the sown seeds were able to germinate in unfenced plots (in unfenced plots germination was 4 and 5%, compared to 57.5 and 63.3% in fenced plots, data for Dengolt and Gelawdios respectively). In the fenced plots, seedling survival was higher (Dengolt = 65 and Gelawdios = 56%) and seedlings grew faster while there was no survival in unfenced plots. This implies that controlling livestock grazing is of paramount importance for both the internal regeneration of church forests and for restoration of the degraded surroundings. The study also explored how tree regeneration varies along the gradient from the forest interior to the edge and open fields, and differs between canopy gaps and closed canopy sites inside the forest. Seedling establishment was more successful inside the forest and in particular in the gaps within the forest. The exposure effect between forest interior and exterior was not analogous to the exposure effect of gaps inside the forest. This result suggests that germination may be primarily influenced by moisture availability along the forest interior-open field gradient. Though seedling establishment is higher inside the forest, seedlings grew more rapidly and survived better on the outer edge of the forest. Our result revealed that the negative effect of edge on regeneration is seen on the inner edge while the outer edge has positive effect on seedlings survival. As a result of the interplay effects of light and moisture, the outer forest edge might become the optimal place for seedling survival and growth. This may indicate that seedlings can colonize and restore the forests on the degraded land from immediate surrounding areas of the church forests, given that the surrounding land is protected from grazing intervention and farming. Within the forest, light in gaps favored survival and growth of seedlings both in dry and wet periods. Perhaps, the soil moisture in gaps inside the forest was not as depleted as that outside the forest in the dry period. In general, the quantitative effect of microsite differed with species. Restoration experiments using management interventions (sowing seeds, planting seedlings, weeding, litter removal, soil scarification) showed that the combined effect of seed sowing and litter removal increased seedling establishment significantly for all the species. This implies that insufficient availability of seeds could be one of the constraints for regeneration in church forests. Weeding did not improve seedling survival and growth of the species, and had even a negative effect on some of them. The future existence of the woody flora and vegetation characteristic of dry Afromontane areas in Ethiopia depends on effective conservation and sustainable utilization of the remnant natural forest patches. If not possible to conserve all remnant forests, selection of church forests across altitudinal variation is important to accommodate most of the species diversity of the area. Maintaining viable populations in the forests and providing connections between forests is pivotal in this respect. Excluding cattle interference and reducing intensity of wood harvest are a prerequisite to facilitate regeneration in church forests. To offset the seed limitation sowing seeds combined with litter removal and slight soil scarification can be very useful. Sowing of seeds should be integrated with active reduction of predation and herbivory (e.g. in the form of enclosures and providing alternative food sources for predators). Seedling transplanting is another alternative to overcome some of the bottlenecks of germination especially moisture deficit and intense seed predation, but weeding might not be needed. Within the forest, opening up of the canopy may be required to facilitate seed germination and seedling performance depending on the species. Along the gradient from forest interior to edge and open field, seed sowing will be effective in the interior microsite, while transplanting seedling in the outer forest edge gives better survival and growth. These measures improve tree regeneration. Interconnecting these remnant forests by vegetation corridors following natural terrain or stream lines, or reducing the distance between them by creating buffer areas and plantations around them, and developing more patches in the landscapes are possible management activities. These will facilitate propagule and germplasm flow and ultimately may sustain these forests and help restoring the surrounding landscape.
    SERK1 links somatic embryogenesis to brassinosteroid signalling
    Kwaaitaal, M.A.C.J. - \ 2007
    Wageningen University. Promotor(en): Sacco de Vries, co-promotor(en): E. Russinova. - [S.l.] : S.n. - ISBN 9789085045830 - 153
    somatische embryogenese - brassinosteroïden - planten - plantenontwikkeling - verjonging - cellen - somatic embryogenesis - brassinosteroids - plants - plant development - regeneration - cells
    Somatic embryogenesis, the phenomenon where a somatic cell supplied with the right cues can re-initiate embryogenesis, reveals the underlying totipotent character of plant cells. The acquisition of this totipotent state coincides with the expression of the Somatic Embryogenesis Receptor Kinase (SERK). Beyond the observation that SERK1 marks competent cells and increases embryogenic competence when overexpressed, the actual signaling cascade that SERK1 is involved in during the acquisition of embryogenic competence is unknown. The major goal of this study is to get a better insight into the function of SERK1 in somatic embryogenesis and in plant development.

    In Chapter 1 an introduction to plant stem cell niches, somatic embryogenesis and recent knowledge about the molecular basis of somatic embryogenesis and SERK1 signalling is provided.

    In Chapter 2, the localization of the SERK1 - Yellow Fluorescent Protein (YFP) fusion protein is described, which coincides with the gene expression pattern as described by Hecht et al (2001). The protein is present in the male and female gametophyte, during sporo- and gametogenesis, in developing embryos and in roots. As observed in protoplasts, also in plants the protein localizes to the plasma membrane.Application of the inhibitor of vesicle trafficking Brefeldin-A revealed that the protein undergoes endocytosis in planta , which is similar to what is seen in protoplasts.

    In Chapter 3, the application of the single molecule technique fluorescence correlation spectroscopy (FCS) on plants expressing the SERK-eYFP protein is described.The diffusion coefficients of SERK1-eYFP and of the membrane marker eYFP-CAAX were determined with FCS. In addition, the mobile fractions of SERK1-eYFP and BRASSINOSTEROID INSENSITIVE 1 (BRI1)-eGFP or BRI1-eYFP were determined in planta and in protoplasts with fluorescence recovery after photobleaching (FRAP).The FRAP measurements show that in contrast to protoplasts, in plants the major part of the SERK1 and BRI1 receptors is immobile.It was found to be possible to apply FCS in planta to determine the diffusion coefficient of plasma membrane localized SERK1-eYFP. When compared with SERK1-eYFP in protoplasts the diffusion coefficient of SERK1-eYFP in planta was significantly lower.

    In Chapter 4, the analysis of SERK1 localization in the vascular tissue is described. It is shown that SERK1 localizes to immature vascular cells, suggested to represent the vascular transit amplifying cells, and including the procambium. As a response to 2,4-D, SERK1 protein levels increase in the vascular cells. Prolonged 2,4-D exposure induces the proliferation of cells from the vascular bundle and SERK1 remains associated with these proliferating cells. In Arabidopsis, the procambium is reported to be the main origin of embryogenic cells, so SERK1 expression in this tissue may mark a plant cell population close to a totipotent state.

    In Chapter 5, experiments are described by which the response of serk1 mutants towards brassinosteroids (BRs) is investigated. It is shown that serk1 mutants have a shift in their responsiveness to BRs. In serk1 serk3 double mutants the sensitivity to BRs is reduced to the level of BRI1 mutants. None of the other SERK family members influences BR sensitivity, suggesting that SERK1 and SERK3 are the only family members redundantly involved in BR signaling.

    In Chapter 6, the cytological analysis of the vascular tissue of the strong serk1-3 mutant allele is described. In the inflorescence stem of adult plants, the serk1-3 mutant shows various vascular defects pointing to an altered procambium activity such as increased vascular differentiation. The serk1-3 vascular phenotype is not clearly influenced by weak bri1 or serk2 mutant alleles. In serk1 serk3 double mutants the vascular defects are partially reversed, suggesting that SERK1 and SERK3 have opposite roles in vascular tissue development.

    In Chapter 7, thestudy of the embryogenic competence of strong and weak serk and bri1 mutants is described. The serk1-3 allele, the bri1-201 and the det2 BR biosynthetic mutant have a marked reduction in embryogenic competence compared to wildtype. So, SERK1 not only marks and enhances embryogenic competence when overexpressed, but is also essential for the acquisition of embryogenic competence. These results suggest that BR signaling is required for the acquisition of embryogenic competence in Arabidopsis.

    In Chapter 8, the results described in the thesis are summarized and discussed and a model is given for the function of SERK1 and BR signaling in regulating cellular pluri- or totipotency.
    Toekomstbomendunning, structuurdunning en noodverjonging; evaluatie van de effecten op het bosecosysteem; een workshop
    Wolf, R.J.A.M. ; Wijk, M.N. van - \ 2006
    Wageningen : Alterra (Alterra rapport 1337.8) - 34
    bomen - bossen - dunnen - ecosystemen - evaluatie - verjonging - trees - forests - thinning - ecosystems - evaluation - regeneration
    Dit rapport doet verslag van een deelonderzoek uit de Evaluatie van effectgerichte maatregelen in multifunctionele bossen 2004-2005 en is gericht op de effecten de maatregelen Aanpassen van de bosvegetatie als overbruggingsmaatregel in het kader van het Overlevingsplan Bos en Natuur (OBN). Omdat de toekomstige bosontwikkeling nog niet door veldonderzoek vastgesteld kan worden, spreken deskundigen in een workshop hierover hun verwachtingen uit over een termijn van 15 jaar. De resultaten van de scorelijsten en de discussies daarover in de expert workshop geven een goed beeld van het langtermijn effect van de maatregelen toekomstbo-mendunning, structuurdunning en noodverjonging op het bosecosysteem. Toekomstbomen-dunning heeft een gering, licht positief, effect op flora en fauna volgens de workshopdeelne-mers. Van structuurdunning wordt wel een duidelijk positief effect verwacht op het bosecosys-teem. De gemiddelde score is positief tot zeer positief. Van noodverjonging wordt ook een dui-delijk positief effect op het bosecosysteem verwacht, maar dit effect is minder groot dan bij de maatregel structuurdunning. De maatregelen worden nu op een manier uitgevoerd die voor de diversiteit van flora en fauna lang niet optimaal is; vooral als een bosteeltkundige ingreep in het multifunctionele bos. Het effect van de maatregelen op flora en fauna kan volgens de deelne-mers aanzienlijk worden verbeterd. Er worden in de workshop een aantal verbeterpunten ge-noemd. Zeker van dood houtinsecten, bodemmicrofauna en rode lijstsoorten wordt aangegeven dat de schattingen onderbouwd zouden moeten worden door veldonderzoek. Dit geldt ook voor een aantal andere soorten.
    De invloed van structuurdunning en noodverjonging op de effectieve depositie in bossen; een literatuurstudie
    Tolkamp, G.W. ; Olsthoorn, A.F.M. - \ 2006
    Wageningen : Alterra (Alterra rapport 1337.7) - 19
    bomen - bossen - dunnen - verjonging - depositie - trees - forests - thinning - regeneration - deposition
    Dit rapport doet verslag van een deelonderzoek uit de Evaluatie van effectgerichte maatregelen in multifunctionele bossen 2004-2005 en is gericht op de effecten de maatregelen Aanpassen van de bosvegetatie als overbruggingsmaatregel in het kader van het Overlevingsplan Bos en Natuur (OBN). Structuurdunning (groepenkap) en noodverjonging (omvorming) hebben via beïnvloeding van de ruwheid van de kroonlaag van het bos in principe een effect op de depositie van verzurende en vermestende stoffen in het bos. De maatregelen worden kort omschreven. Doel van dit deelrapport is om de effecten van de beide maatregelen op de depositie in te schatten via literatuurstudie. Het niveau van depositie is hoger in bosranden en mede afhankelijk van de lengte en type begroeiing van het gebied vóór het bos. Door filtering in de bosrand slaat er verderop minder depositie neer. Er zijn vele literatuurbronnen die deze effecten beschrijven en kwantificeren voor specifieke situaties. Een algemeen beeld voor de netto effecten op de depositie is daarvan moeilijk af te leiden door de vele tijdgebonden en kleinschalige effecten. Voor de depositie hebben de beide maatregelen dus waarschijnlijk geen netto effect. Bovendien is het effect van structuurdunning en noodverjonging op de ruwheid van het kronendak in principe tijdelijk vanwege het opgroeien van de verjonging die het gat opvult. De beide maatregelen zullen vooral ingezet moeten worden om de stabiliteit en diversiteit van het bos te verhogen.
    Structuurdunning en noodverjonging; evaluatie van de mate van doelrealisatie; een veldonderzoek
    Wolf, R.J.A.M. ; Schraven, R. - \ 2006
    Wageningen : Alterra (Alterra rapport 1337.6) - 55
    bomen - bossen - dunnen - evaluatie - experimenten - verjonging - trees - forests - thinning - evaluation - experiments - regeneration
    Dit rapport doet verslag van een deelonderzoek uit de Evaluatie van effectgerichte maatregelen in multifunctionele bossen 2004-2005 en is gericht op de effecten de maatregelen Aanpassen van de bosvegetatie als overbruggingsmaatregel in het kader van het Overlevingsplan Bos en Natuur (OBN). De maatregelen structuurdunning en noodverjonging zijn, op enkele uitzonderin-gen na, uitgevoerd conform de wijze waarop deze binnen het OBN is gedefinieerd. In een deel van de gevallen doen de aangeplante boompjes het matig tot (soms) slecht. Dit betekent dat de perspectieven voor houtproductie in deze delen slecht zijn. Beide maatregelen hebben een dui-delijke positieve bijdrage geleverd aan de realisatie van alle OBN subdoelen. Sommige eigen-schappen zijn niet veranderd. De boskenmerken die in positieve zin zijn veranderd hebben voornamelijk betrekking op de bosstructuur en de boomsoortensamenstelling. De verandering is hier meestal een direct (logisch) gevolg van de uitvoering van de maatregel. Het onderzoek heeft inzicht gegeven in de mate en aard van deze veranderingen. In de toekomst zou ontmen-ging van het jonge bos mogelijk kunnen leiden tot minder variatie (minder boomsoorten, minder menging in bosperceel), met name wanneer in de verjongde gedeelten de hoofdboomsoort van de oude opstand gaat domineren. Er worden een aantal aanbevelingen geformuleerd ter opti-malisatie van de maatregel.
    Beheersing van de iepenziekte in bossen met een natuurdoelstelling. Verslag van een onderzoek, uigevoerd in het Lauwersmeergebied
    Kopinga, J. - \ 2006
    Wageningen : Alterra (Alterra-rapport 1323) - 47
    ulmaceae - ulmus - ophiostoma - plantenziekteverwekkende schimmels - plantenziektebestrijding - ringen van planten (ringing) - verjonging - feromonen - coleoptera - nederland - lauwersmeergebied - ulmaceae - ulmus - ophiostoma - plant pathogenic fungi - plant disease control - ringing - regeneration - pheromones - coleoptera - netherlands - lauwersmeergebied
    Regeneratie van de gevelde iepen uit de opslag van wortels of stobben is vaak een probleem om iepen definitief uit een gemengde beplanting te verwijderen. Tenzij gebruik wordt gemaakt van chemische middelen, maar dat is in beplantingen met een natuurdoelstelling ongewenst. Een mogelijk alternatieve methode is dan het ringen van de bomen waarbij ingegrepen wordt op de opslag van reservestoffen die de boom benut bij de vorming van opslag. Van de werking van deze methode bij iep is nog weinig bekend . Dit rapport beschrijft de opzet, uitvoering en eerste resultaten van praktijkonderzoek. Bij dit onderzoek speelde tevens de vraag in hoeverre en hoelang een beplanting met zieke iepen als potentiële besmettingshaard een bedreiging kan vormen voor nog gezonde iepenbeplantingen in de wijdere omgeving. Dit aspect is onderzocht aan de hand van een netwerk van rond een besmet haardgebied geplaatste feromoonvallen voor de iepenspintkever. Door het ringen wordt de natuurlijke regeneratie geremd, maar de resultaten na ruim een jaar onderzoek laten nog niet toe om hierover meer gedefinieerde en gekwantificeerde uitspraken te doen. Bij betrekkelijk geringe populatiedichtheden van de iepenspintkever, zoals die zich voordoen in het Lauwersmeergebied, zijn significante verhogingen daarvan vooralsnog alleen merkbaar c.q. meetbaar binnen afstanden van slechts enkele kilometers van een haardgebied
    Verjonging van Juniperus communis L. (Cupressaceae, Pinopsida): wat is mythe, wat is waar?
    Haveman, R. - \ 2005
    Stratiotes 31 (2005). - ISSN 0928-2297 - p. 20 - 24.
    heidegebieden - verjonging - juniperus communis - habitats - veluwe - heathlands - regeneration - juniperus communis - habitats - veluwe
    Dit artikel geeft resultaten van veldonderzoek op militaire terreinen op de Veluwe (Oldebroek, Doornspijk). Het blijkt, dat er sprake is van verjonging van jeneverbessen in heidevegetaties
    Gaten in het bosbeheer
    Wijdeven, S.M.J. ; Willems, A.J.H. ; Groot Bruinderink, G.W.T.A. - \ 2004
    Vakblad Natuur Bos Landschap 1 (2004)8. - ISSN 1572-7610 - p. 18 - 19.
    bosbouw - bosbeheer - verjonging - natuurlijke verjonging - velling - kaalslag - geïntegreerde systemen - opstandskenmerken - opstandsstructuur - opstandsontwikkeling - bossen - botanische samenstelling - bosecologie - gaten in het kroondak - soortendiversiteit - biodiversiteit - bosopstanden - geïntegreerd bosbeheer - forestry - forest administration - regeneration - natural regeneration - felling - clear felling - integrated systems - stand characteristics - stand structure - stand development - forests - botanical composition - forest ecology - canopy gaps - species diversity - biodiversity - forest stands - integrated forest management
    Pleidooi voor het toepassen van grotere gaten bij de natuurlijke verjonging van bosopstanden. In de huidige praktijk wordt geïntegreerd bosbeheer veelal ingevuld door kleinschalige ingrepen, afgestemd op het opstandsniveau. Weliswaar verhoogt dit op dit schaalniveau (de plek of de opstand) de variatie, maar het leidt tot een meer uniforme situatie op het niveau van terreindelen en de beheerseenheid. Grote verjongingsgaten hebben niet alleen een specifiek effect op de soortensamenstelling en structuur van de verjonging, maar zijn ook van belang voor andere soorten, zoals kruiden, korstmossen, reptielen, insecten, vogels en grote hoefdieren, en leveren daarmee een bijdrage aan vergroting van de biodiversiteit en de belevingswaarde
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