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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    Molecular characterization of Pseudomonas from Agaricus bisporus caps reveal novel blotch pathogens in Western Europe
    Taparia, T. ; Krijger, M.C. ; Haynes, Edward ; Elphinstone, J.G. ; Noble, R. ; Wolf, J.M. van der - \ 2020
    BMC Genomics 21 (2020). - ISSN 1471-2164
    Background: Bacterial blotch is a group of economically important diseases affecting the cultivation of common button mushroom, Agaricus bisporus. Despite being studied for more than a century, the identity and nomenclature of blotch-causing Pseudomonas species is still unclear. This study aims to molecularly characterize the phylogenetic and phenotypic diversity of blotch pathogens in Western Europe.
    Methods: In this study, blotched mushrooms were sampled from farms across the Netherlands, United Kingdom and Belgium. Bacteria were isolated from symptomatic cap tissue and tested in pathogenicity assays on fresh caps and in pots. Whole genome sequences of pathogenic and non-pathogenic isolates were used to establish phylogeny via multi-locus sequence alignment (MLSA), average nucleotide identity (ANI) and in-silico DNA:DNA hybridization (DDH) analyses. Results: The known pathogens “Pseudomonas gingeri”, P. tolaasii, “P. reactans” and P. costantinii were recovered from blotched mushroom caps. Seven novel pathogens were also identified, namely, P. yamanorum, P. edaphica, P. salomonii and strains that clustered with Pseudomonas sp. NC02 in one genomic species, and three nonpseudomonads, i.e. Serratia liquefaciens, S. proteamaculans and a Pantoea sp. Insights on the pathogenicity and symptom severity of these blotch pathogens were also generated.
    Conclusion: A detailed overview of genetic and regional diversity and the virulence of blotch pathogens in Western Europe, was obtained via the phylogenetic and phenotypic analyses. This information has implications in the study of symptomatic disease expression, development of diagnostic tools and design of localized strategies for disease management.
    Comparisons with wheat reveal root anatomical and histochemical constraints of rice under water-deficit stress
    Ouyang, Wenjing ; Yin, Xinyou ; Yang, Jianchang ; Struik, Paul C. - \ 2020
    Plant and Soil 452 (2020). - ISSN 0032-079X - p. 547 - 568.
    Lignin - Rice - Root anatomy - Root morphology - Suberin - Water deficit - Wheat

    Aims: To face the challenge of decreasing freshwater availability for agriculture, it is important to explore avenues for developing rice genotypes that can be grown like dryland cereals. Roots play a key role in plant adaptation to dry environments. Methods: We examined anatomical and histochemical root traits that affect water acquisition in rice (Oryza sativa) and wheat (Triticum aestivum). These traits and root growth were measured at two developmental stages for three rice and two wheat cultivars that were grown in pots under three water regimes. Results: Wheat roots had larger xylem sizes than rice roots, which potentially led to a higher axial conductance, especially under water-deficit conditions. Suberization, lignification and thickening of the endodermis in rice roots increased with increasing water deficit, resulting in stronger radial barriers for water flow in rice than in wheat, especially near the root apex. In addition, water deficit strongly impeded root growth and lateral root proliferation in rice, but only slightly in wheat, and cultivars within a species differed little in these responses. The stress sensitivity of rice attributes was slightly more prominent at vegetative than at flowering stages. Conclusions: Rice root characteristics, which are essential for growth under inundated conditions, are not conducive to growth under water deficit. Although rice roots show considerable plasticity under different watering regimes, improving root xylem size and reducing the radial barriers would be required if rice is to grow like dryland cereals.

    Comparison of the individual salinity and water deficit stress using water use, yield, and plant parameters in maize
    Bazrafshan, Abouzar ; Shorafa, Mehdi ; Mohammadi, Mohammad Hossein ; Zolfaghari, Ali Asghar ; Craats, Daniël van de; Zee, Sjoerd E.A.T.M. van der - \ 2020
    Environmental Monitoring and Assessment 192 (2020). - ISSN 0167-6369
    Abiotic stresses - Evaporative demand - Root system - Water uptake

    Though water deficit and salinity effects on plants have similarities, they are physiologically different. This motivated us to separately explore the effects of salinity and water deficit on water consumption, yield, and some plant parameters for maize (Zea mays L., var. SC704). Greenhouse experiments were conducted during two seasons. In one experiment, maize was cultivated in wet soil (matric potential of − 10 kPa), and the irrigation water salinity was varied between treatments (osmotic potentials up to − 336 kPa). In a parallel experiment, five water deficit levels were maintained by irrigating with water to accomplish the same daily water uptake as in the salinity treatments. The experiments were conducted in pots with a randomized design and four replicates. Salinity and water deficit stress significantly affected yield and other plant parameters. However, root dry matter in autumn was not significant. We observed a profound effect of evaporative demand on most of the plant parameters and water use, such as water use efficiency (WUE). For same water use rate, the values of osmotic and matric potential were different. In spring season, the ratios of matric to osmotic potential were 0.25, 0.46, 0.44, and 0.43 in corresponding D1, D2, D3, and D4 water deficit and S1, S2, S3, and S4 salinity treatments. For autumn season, these ratios were 0.26, 0.36, 0.34, and 0.36. We concluded crop models that lump water deficit and salinity (additively or multiplicatively) to predict yields can result in inappropriate predictions.

    Responses of Lowland, Upland and Aerobic Rice Genotypes to Water Limitation During Different Phases
    Vijayaraghavareddy, Preethi ; Xinyou, Yin ; Struik, Paul C. ; Makarla, Udayakumar ; Sreeman, Sheshshayee - \ 2020
    Rice Science 27 (2020)4. - ISSN 1672-6308 - p. 345 - 354.
    Aerobic - Oryza sativa - Phenology - Upland - Water limitation - yield

    Rice yield reduction due to water limitation depends on its severity and duration and on the phenological stage of its occurrence. We exposed three contrasting rice genotypes, IR64, UPLRi7 and Apo (adapted to lowland, upland and aerobic conditions, respectively), to three water regimes (puddle, 100% and 60% field capacity) in pots during the vegetative (GSI), flowering (GSII) and grain filling (GSIII) stages. Stress at all the three stages significantly reduced yield especially in lowland genotype IR64. Effect of water limitation was more severe at GSII than at the other two stages. Stress at GSI stage reduced both source activity (leaf area and photosynthetic rate) and sink capacity (tiller number or panicle number per pot). When stress was imposed at GSII, spikelet fertility was most affected in all the three genotypes. In both GSII and GSIII, although leaf area was constant in all the three water regimes, estimated relative whole-plant photosynthesis was strongly associated with yield reduction. Reduced photosynthesis due to stress at any given stage was found to have direct impact on yield. Compared to the other genotypes, Apo had deeper roots and maintained a better water relation, thus, higher carbon gain and spikelet viability, and ultimately, higher biomass and productivity under water-limited conditions. Therefore, screening for these stage-dependent adaptive mechanisms is crucial in breeding for sustained rice production under water limitation.

    Mycorrhizal impacts on root trait plasticity of six maize varieties along a phosphorus supply gradient
    Wang, Xin-Xin ; Li, Hongbo ; Chu, Qun ; Feng, Gu ; Kuyper, Thomas W. ; Rengel, Zed - \ 2020
    Plant and Soil 448 (2020). - ISSN 0032-079X - p. 71 - 86.
    Morphological traits - Physiological traits - Root/shoot ratio - Specific root length

    Background and aims: Plasticity of plants refers to their ability to produce different phenotypes in different environments. Plants show plasticity aboveground as well as belowground. The influence of the arbuscular mycorrhizal fungal (AMF) symbiosis on root plasticity is poorly known. This study aimed to quantify plasticity of root-system related, morphological, physiological or mycorrhizal traits along a soil phosphorus (P) supply gradient. Methods: Six varieties of maize (Zea mays L.) were grown in pots with or without AMF at five rates of P supply. Fifteen root traits were measured and calculated after seven weeks of growth. Results: Root system traits (biomass and length) and physiological traits (phosphatase activity at the root surface and in the rhizosphere) showed high plasticity along the P gradient, whereas morphological traits (specific root length and root diameter) exhibited low plasticity. Mycorrhizal presence reduced root-system plasticity (biomass and length), increased morphological-trait plasticity (specific root length and proportion of fine roots), but had little effects on other traits. Conclusion: Our results indicate that trait plasticity related to the root system constitutes the most important adaptive strategy for maize to variation in P supply, and that the mycorrhizal symbiosis reduces root-system plasticity.

    Temporal Variation of Ammonium in Sulfic Tropaquept Cultivated with Rice in Experimental Pots
    Nurulhuda, K. ; Husni, M.H.A. ; Zawawi, M.A.M. ; Zakaria, M.P. ; Struik, P.C. ; Keesman, K.J. - \ 2019
    In: Konvensyen Kebangsaan KejuruteraanPertanian Dan Makanan 2019, Mac 2019, Wisma Tani, Kementerian Pertanian dan Industri Asas Tani Malaysia, Putrajaya. - - p. 32 - 35.
    Hypothetically, monitoring of soil solution NH4+-N dynamics may allow estimation of nitrogen (N) transformation rates such as the rates of nitrification, denitrification, mineralisation and immobilisation. Such observations can be used to evaluate and improve performance of N dynamics models for flooded rice systems. Therefore, the objective of this study was to evaluate temporal variation of ammonium dynamics in fertilised and flooded rice pots. Concentrations of NH4+-N were determined in soil solutions that were extracted by MacroRhizon samplers. MacroRhizon is a soil solution sampler with a pore size of 0.15 μm manufactured by Rhizosphere Research, the Netherlands. In comparison to typical soil sampling methods, some advantages of using MacroRhizon are repeated sampling at the same spot possible, easy to install and less disturbance to the soil due to the small diameter, and maximum pore size of 0.2 μm which requires no further filtering prior to chemical analysis. Results showed that under current agronomic and management practices, broadcast N application had no obvious and consistent influence on soil solution NH4+-N. Analysis of the results suggest that suitability of soil solutions extracted using the MacroRhizon samplers as alternatives for the labourious and destructive conventional soil samplings is subject to further investigation.
    Genetic Interaction Studies Reveal Superior Performance of Rhizobium tropici CIAT899 on a Range of Diverse East African Common Bean (Phaseolus vulgaris L.) Genotypes
    Gunnabo, A.H. ; Geurts, R. ; Wolde-Meskel, E. ; Degefu, T. ; Giller, K.E. ; Heerwaarden, J. van - \ 2019
    Applied and Environmental Microbiology 85 (2019)24. - ISSN 0099-2240
    bean genotypes - genotype-by-strain interaction - N2 fixation - nodulation - Rhizobium strains

    We studied symbiotic performance of factorial combinations of diverse rhizobial genotypes (GR) and East African common bean varieties (GL) that comprise Andean and Mesoamerican genetic groups. An initial wide screening in modified Leonard jars (LJ) was followed by evaluation of a subset of strains and genotypes in pots (contained the same, sterile medium) in which fixed nitrogen was also quantified. An additive main effect and multiplicative interaction (AMMI) model was used to identify the contribution of individual strains and plant genotypes to the GL × GR interaction. Strong and highly significant GL × GR interaction was found in the LJ experiment but with little evidence of a relation to genetic background or growth habits. The interaction was much weaker in the pot experiment, with all bean genotypes and Rhizobium strains having relatively stable performance. We found that R. etli strain CFN42 and R. tropici strains CIAT899 and NAK91 were effective across bean genotypes but with the latter showing evidence of positive interaction with two specific bean genotypes. This suggests that selection of bean varieties based on their response to inoculation is possible. On the other hand, we show that symbiotic performance is not predicted by any a priori grouping, limiting the scope for more general recommendations. The fact that the strength and pattern of GL × GR depended on growing conditions provides an important cautionary message for future studies.IMPORTANCE The existence of genotype-by-strain (GL × GR) interaction has implications for the expected stability of performance of legume inoculants and could represent both challenges and opportunities for improvement of nitrogen fixation. We find that significant genotype-by-strain interaction exists in common bean (Phaseolus vulgaris L.) but that the strength and direction of this interaction depends on the growing environment used to evaluate biomass. Strong genotype and strain main effects, combined with a lack of predictable patterns in GL × GR, suggests that at best individual bean genotypes and strains can be selected for superior additive performance. The observation that the screening environment may affect experimental outcome of GL × GR means that identified patterns should be corroborated under more realistic conditions.

    GEM model for soilless cultures: review of process descriptions and suggestions for improvement
    Boesten, J.J.T.I. ; Wipfler, E.L. ; Os, E.A. van; Hoogsteen, M. - \ 2019
    Wageningen : Wageningen Environmental Research (Report / Wageningen Environmental Research 2950) - 67
    The GEM model developed for soilless cultures consists of different submodels (A) for applications to crops grown on mats by drip irrigation, (B) for spray applications to crops grown on such mats, and (C) is for spray applications to crops grown in pots in an ebb/flood system (GEM-A, GEM-B, and GEM-C). The descriptions of the processes for pesticide behaviour in these submodels were reviewed, considering also their consistency with measurements available in the literature. For GEM-A it is recommended to include sorption to the mats, the foil surrounding the mats and the irrigation pipes and to include partitioning between the water in the mats and the plant roots. For GEM-B it is recommended to include direct contamination of the substrate mats and the troughs resulting from spray and Low Volume Mister (LVM) applications. For GEM-B and GEM-C it is recommended (i) to revise the procedures for calculating the initial concentrations in the air and the condensation water, (ii) to include deposition onto the roof by spray and LVM applications, (iii) to revise the procedure for calculating the volatilisation rates from the plant surfaces. For GEM-C it is recommended (i) to omit the sorption equilibration between the bottom 10 cm of the soil in the pots and the water on the ebb/flood tables, (ii) to revise the procedure for the flux in the gas phase between the greenhouse air and the top layer of the soil in the pots, and (iii) to use a crop-specific value for the fraction of the surface area covered by the pots.
    Feedbacks of plant identity and diversity on the diversity and community composition of rhizosphere microbiomes from a long-term biodiversity experiment
    Schmid, Marc W. ; Hahl, Terhi ; Moorsel, Sofia J. van; Wagg, Cameron ; Deyn, Gerlinde B. De; Schmid, Bernhard - \ 2019
    Molecular Ecology 28 (2019)4. - ISSN 0962-1083 - p. 863 - 878.
    16S rRNA gene sequencing - legacy effects - plant diversity - rhizosphere microbiome - soil microbial diversity

    Soil microbes are known to be key drivers of several essential ecosystem processes such as nutrient cycling, plant productivity and the maintenance of plant species diversity. However, how plant species diversity and identity affect soil microbial diversity and community composition in the rhizosphere is largely unknown. We tested whether, over the course of 11 years, distinct soil bacterial communities developed under plant monocultures and mixtures, and if over this time frame plants with a monoculture or mixture history changed in the bacterial communities they associated with. For eight species, we grew offspring of plants that had been grown for 11 years in the same field monocultures or mixtures (plant history in monoculture vs. mixture) in pots inoculated with microbes extracted from the field monoculture and mixture soils attached to the roots of the host plants (soil legacy). After 5 months of growth in the glasshouse, we collected rhizosphere soil from each plant and used 16S rRNA gene sequencing to determine the community composition and diversity of the bacterial communities. Bacterial community structure in the plant rhizosphere was primarily determined by soil legacy and by plant species identity, but not by plant history. In seven of the eight plant species the number of individual operational taxonomic units with increased abundance was larger when inoculated with microbes from mixture soil. We conclude that plant species richness can affect below-ground community composition and diversity, feeding back to the assemblage of rhizosphere bacterial communities in newly establishing plants via the legacy in soil.

    Native arbuscular mycorrhizal fungi increase the abundance of ammonia-oxidizing bacteria, but suppress nitrous oxide emissions shortly after urea application
    Teutscherova, Nikola ; Vazquez, Eduardo ; Arango, Jacobo ; Arevalo, Ashly ; Benito, Marta ; Pulleman, Mirjam - \ 2019
    Geoderma 338 (2019). - ISSN 0016-7061 - p. 493 - 501.
    Arbuscular mycorrhizal fungi - Nitrification - Nitrous oxide - Tropical grasses - Urea

    The potential of the symbiosis between plants and arbuscular mycorrhizal fungi (AMF) to reduce emissions of the greenhouse gas N2O has gained scientific attention in the last years. Given the high nitrogen (N) requirements of AMF and their role in plant N uptake, they may reduce the availability of mineral N that could be subject to N2O emissions and leaching losses. We investigated the impact of AMF on the growth of tropical grass Brachiaria decumbens Stapf. and on N2O released after fertilization with urea in a mesocosm study. To evaluate the role of nitrification in N2O emissions, we used nitrification inhibitor dicyandiamide (DCD). The study included a full-factorial design (n = 6) with two AMF treatments (with and without AMF inoculation) and three fertilization treatments (control, urea and urea + DCD), applied after 92 days of growth. Plant growth, soil properties and N2O emissions were measured during the following 2 weeks and the abundance of nitrifiers was quantified one and two weeks after fertilization. The production of N2O increased after urea application but only without DCD, indicating the importance of nitrification in N2O emissions. The emissions of N2O after urea application were reduced by 46% due to the presence of AMF. Nevertheless, the abundance of ammonia-oxidizing bacteria (AOB) was increased by urea and AMF, while plant growth was reduced by the AMF. The increased root:shoot ratio of the biomass in AMF pots suggests competition between AMF and plants. This study demonstrated that immobilization of N by AMF can reduce N2O emissions after fertilization, even when plant growth is reduced. The inverse relationship between (higher) AOB abundance and (lower) nitrification rates suggests that changes in the activity of AOB, rather than abundance, may be indicative of the impact of the AMF-Brachiaria symbiosis on N cycling in tropical grasslands. Alternatively, the difference between N2O emissions from AMF and non-AMF pots may be explained by increased reduction of N2O in the presence of AMF. Longer-term studies are needed to verify whether the effects of AMF on N2O emissions and/or plant growth persist over time or are limited to initial immobilization of N by AMF in N-limited systems.

    Soil community conditioning by 8 Geranium species
    Wilschut, Rutger ; Putten, Wim van der; Garbeva, Paolina ; Harkes, Paula ; Konings, W. ; Kulkarni, Purva ; Martens, Henk ; Geisen, Stefan - \ 2018
    Netherlands Institute of Ecology (NIOO-KNAW)
    PRJEB29769 - Geranium - ERP112117
    In this study we examined communities of bacteria, protists, fungi and nematodes in the rhizospheres of 8 Geranium species. We grew the plants for 14 weeks in pots with soils from 5 different riverine grasslands close to Wageningen, The Netherlands, after which we extracted and amplified DNA using 16S and 18S rDNA primers, to explore variation in the microbiomes.
    Data from: Spatial heterogeneity in plant-soil feedbacks alters competitive interactions between two grassland plant species
    Xue, Wei ; Berendse, F. ; Bezemer, T.M. - \ 2018
    Wageningen UR
    soil heterogeneity - plant-soil feedback - intra- and interspecific competition - plant-plant interactions - plant-soil interactions - soil origin - soil nutrient - patchy distribution
    1. The effects of plants on soil vary greatly between plant species and in mixed plant communities this can lead to spatial variation in plant-soil feedback (PSF) effects. Such spatial effects are thought to influence plant species coexistence, but the empirical evidence for this hypothesis is limited. 2. Here, we investigate how spatial heterogeneity in PSFs influences plant growth and competition. The experiment was carried out with high and low nutrient soils to examine how these effects depend on soil fertility. We collected soil from field plots planted for three years with monocultures of Anthoxanthum odoratum and Centaurea jacea and tested the performance of the two species in a greenhouse experiment in heterogeneous soils consisting of patches of “own” and “foreign” soils and in soils where the “own” and “foreign” soils were mixed homogeneously. In the test phase, plants were grown in monocultures and in 1:1 mixtures in live or sterilized soils. 3. Overall, A. odoratum in monocultures produced less aboveground biomass in heterogeneous soils than in homogeneous soils. Centaurea jacea produced less belowground biomass in live heterogeneous soils than in live homogeneous soils, but there was no difference between sterile heterogeneous and homogeneous soils. The belowground biomass per patch varied more in pots with live heterogeneous soils than in pots with live homogeneous soils for both plant species, but there was no difference between pots with sterile heterogeneous and homogeneous soils. In pots with plant mixtures, the difference in aboveground biomass between the two competing species tended to be smaller in heterogeneous than in homogeneous soils. In pots with heterogeneous soils, both plant species grown in mixtures produced more aboveground biomass in “foreign” soil patches than in “own” soil patches. The responses of plants to heterogeneous PSFs were not different between low and high nutrient soils. 4. Our results show that spatially heterogeneous PSFs can influence plant performance and competition via reducing the growth inequality between the two competing species by allowing selective growth in foreign soil patches, independent of initial soil nutrient availability. Such effect may slow down exclusion processes and thus promote the coexistence of competing species at the local scale in mixed plant communities.
    Spatial heterogeneity in plant–soil feedbacks alters competitive interactions between two grassland plant species
    Xue, Wei ; Berendse, Frank ; Bezemer, T.M. - \ 2018
    Functional Ecology 32 (2018)8. - ISSN 0269-8463 - p. 2085 - 2094.
    intra- and interspecific competition - patchy distribution - plant–plant interactions - plant–soil feedback - plant–soil interactions - soil heterogeneity - soil nutrient - soil origin

    The effects of plants on soil vary greatly between plant species and in mixed plant communities this can lead to spatial variation in plant-soil feedback (PSF) effects. Such spatial effects are thought to influence plant species coexistence, but the empirical evidence for this hypothesis is limited. Here, we investigate how spatial heterogeneity in PSFs influences plant growth and competition. The experiment was carried out with high and low nutrient soils to examine how these effects depend on soil fertility. We collected soil from field plots planted for three years with monocultures of Anthoxanthum odoratum and Centaurea jacea and tested the performance of the two species in a greenhouse experiment in heterogeneous soils consisting of patches of “own” and “foreign” soils and in soils where the “own” and “foreign” soils were mixed homogeneously. In the test phase, plants were grown in monocultures and in 1:1 mixtures in live or sterilized soils. Overall, A. odoratum in monocultures produced less aboveground biomass in heterogeneous soils than in homogeneous soils. Centaurea jacea produced less belowground biomass in live heterogeneous soils than in live homogeneous soils, but there was no difference between sterile heterogeneous and homogeneous soils. The belowground biomass per patch varied more in pots with live heterogeneous soils than in pots with live homogeneous soils for both plant species, but there was no difference between pots with sterile heterogeneous and homogeneous soils. In pots with plant mixtures, the difference in aboveground biomass between the two competing species tended to be smaller in heterogeneous than in homogeneous soils. In pots with heterogeneous soils, both plant species grown in mixtures produced more aboveground biomass in “foreign” soil patches than in “own” soil patches. The responses of plants to heterogeneous PSFs were not different between low and high nutrient soils. Our results show that spatially heterogeneous PSFs can influence plant performance and competition via reducing the growth inequality between the two competing species by allowing selective growth in foreign soil patches, independent of initial soil nutrient availability. Such effect may slow down exclusion processes and thus promote the coexistence of competing species at the local scale in mixed plant communities. A plain language summary is available for this article.

    Density-dependency and plant-soil feedback : former plant abundance influences competitive interactions between two grassland plant species through plant-soil feedbacks
    Xue, Wei ; Bezemer, T.M. ; Berendse, Frank - \ 2018
    Plant and Soil 428 (2018)441-452. - ISSN 0032-079X - p. 441 - 452.
    Interspecific competition - Intraspecific competition - Plant abundance - Plant density - Plant-soil feedbacks - Plant-soil interactions - Soil biota

    Backgrounds and aims: Negative plant-soil feedbacks (PSFs) are thought to promote species coexistence, but most evidence is derived from theoretical models and data from plant monoculture experiments. Methods: We grew Anthoxanthum odoratum and Centaurea jacea in field plots in monocultures and in mixtures with three ratios (3:1, 2:2 and 1:3) for three years. We then tested in a greenhouse experiment the performance of A. odoratum and C. jacea in pots planted with monocultures and 1:1 mixtures and filled with live and sterile soils collected from the field plots. Results: In the greenhouse experiment, C. jacea produced less aboveground biomass in soil conditioned by C. jacea monocultures than in soil conditioned by A. odoratum monocultures, while the aboveground biomass of A. odoratum in general did not differ between the two monospecific soils. The negative PSF effect was greater in the 1:1 plant mixture than in plant monocultures for A. odoratum but did not differ for C. jacea. In the greenhouse experiment, the performance of C. jacea relative to A. odoratum in the 1:1 plant mixture was negatively correlated to the abundance of C. jacea in the field plot where the soil was collected from. This relationship was significant both in live and sterile soils. However, there was no relationship between the performance of A. odoratum relative to C. jacea in the 1:1 plant mixture in the greenhouse experiment and the abundance of A. odoratum in the field plots. Conclusions: The response of a plant to PSF depends on whether the focal species grows in monocultures or in mixtures and on the identity of the species. Interspecific competition can exacerbate the negative plant-soil feedbacks compared to intraspecific competition when a plant competes with a stronger interspecific competitor. Moreover, the abundance of a species in mixed plant communities, via plant-soil feedback, negatively influences the relative competitiveness of that species when it grows later in interspecific competition, but this effect varies between species. This phenomenon may contribute to the coexistence of competing plants under natural conditions through preventing the dominance of a particular plant species.

    Ashes from fluidized bed combustion of residual forest biomass : recycling to soil as a viable management option
    Cruz, Nuno C. ; Rodrigues, Sónia M. ; Carvalho, Lina ; Duarte, Armando C. ; Pereira, Eduarda ; Romkens, Paul ; Tarelho, Luís A.C. - \ 2017
    Environmental Science and Pollution Research 24 (2017)17. - ISSN 0944-1344 - p. 14770 - 14781.
    Bottom ash - Fly ash - Portugal - Recycling - Soil amendment
    Although bottom ash (BA) [or mixtures of bottom and fly ash (FA)] from clean biomass fuels is currently used as liming agent, additive for compost, and fertilizer on agricultural and forest soils in certain European countries, in several other countries most of the ashes are currently disposed in landfills. This is due to both a lack of a proper classification of the materials and of regulatory barriers. Chemical characterization including analysis of an array of potentially toxic elements (PTEs) proved that over 100,000 tons of BA currently landfilled every year in Portugal actually complied with legal limits for PTEs for soil fertilizers applied in other countries. Pot experiments were conducted, testing three dosages of BA and FA (1, 2.5, and 5%, in weight) in three mining soils with different properties. Additions of ash materials to soils led to an increase in the pore water pH relative to control pots (0% of ash added) and had a clear impact on DOC and on the solubilization of both macro- and micronutrients (notably Cu). The results from the case study using BA and FA from a Portuguese biomass thermal power plant demonstrate that it is imperative to further develop a regulatory framework to alleviate technological and environmental barriers for biomass ash utilization as raw material for fertilizers and/or soil liming agent, in accordance with the goals of the circular economy. A more harmonized view on how to assess the merits and risks of the re-use of these materials is also needed.
    Comparison of soil water potential sensors: a drying experiment
    Degre, Aurore ; Ploeg, M.J. van der; Caldwell, Todd ; Gooren, H.P.A. - \ 2017
    Vadose Zone Journal 16 (2017)4. - ISSN 1539-1663 - 8 p.
    The soil water retention curve (WRC) plays a major role in a soil’s hydrodynamic behavior. Many measurement techniques are currently available for determining the WRC in the laboratory. Direct in situ WRC can be obtained from simultaneous soil moisture and water potential readings covering a wide tension range, from saturation to the wilting point. There are many widely used soil moisture probes. Whereas near-saturation tension can be measured using water-filled tensiometers, wider ranges of water potential require new, more expensive, and less widely used probes. We compared three types of soil water potential sensors that could allow us to measure water potential in the field, with a range relevant to water uptake by plants. Polymer tensiometers (POTs), MPS-2 probes, and pF meters were compared in a controlled drying experiment. The study showed that the POTs and MPS-2 probes had good reliability in their respective ranges. Combined with a soil moisture probe, these two sensors can provide observed WRCs. The pF meters below −30 kPa were inaccurate, and their response was sensitive to measurement interval, with greater estimated suction at shorter measurement intervals. In situ WRC can provide supplementary information, particularly with regard to its spatial and temporal variability. It could also improve the results of other measurement techniques, such as geophysical observations.
    Maximum Plant Uptakes for Water, Nutrients, and Oxygen Are Not Always Met by Irrigation Rate and Distribution in Water-based Cultivation Systems
    Blok, Chris ; Jackson, Brian E. ; Guo, Xianfeng ; Visser, Pieter H.B. De; Marcelis, Leo F.M. - \ 2017
    Frontiers in Plant Science 8 (2017). - ISSN 1664-462X
    Growing on rooting media other than soils in situ -i.e., substrate-based growing- allows for higher yields than soil-based growing as transport rates of water, nutrients, and oxygen in substrate surpass those in soil. Possibly water-based growing allows for even higher yields as transport rates of water and nutrients in water surpass those in substrate, even though the transport of oxygen may be more complex. Transport rates can only limit growth when they are below a rate corresponding to maximum plant uptake. Our first objective was to compare Chrysanthemum growth performance for three water-based growing systems with different irrigation. We compared; multi-point irrigation into a pond (DeepFlow); one-point irrigation resulting in a thin film of running water (NutrientFlow) and multi-point irrigation as droplets through air (Aeroponic). Second objective was to compare press pots as propagation medium with nutrient solution as propagation medium. The comparison included DeepFlow water-rooted cuttings with either the stem 1 cm into the nutrient solution or with the stem 1 cm above the nutrient solution. Measurements included fresh weight, dry weight, length, water supply, nutrient supply, and oxygen levels. To account for differences in radiation sum received, crop performance was evaluated with Radiation Use Efficiency (RUE) expressed as dry weight over sum of Photosynthetically Active Radiation. The reference, DeepFlow with substrate-based propagation, showed the highest RUE, even while the oxygen supply provided by irrigation was potentially growth limiting. DeepFlow with water-based propagation showed 15–17% lower RUEs than the reference. NutrientFlow showed 8% lower RUE than the reference, in combination with potentially limiting irrigation supply of nutrients and oxygen. Aeroponic showed RUE levels similar to the reference and Aeroponic had non-limiting irrigation supply of water, nutrients, and oxygen. Water-based propagation affected the subsequent cultivation in the DeepFlow negatively compared to substrate-based propagation. Water-based propagation resulted in frequent transient discolorations after transplanting in all cultivation systems, indicating a factor, other than irrigation supply of water, nutrients, and oxygen, influencing plant uptake. Plant uptake rates for water, nutrients, and oxygen are offered as a more fundamental way to compare and improve growing systems.
    Cultural significance of termites in sub-Saharan Africa
    Huis, Arnold van - \ 2017
    Journal of Ethnobiology and Ethnomedicine 13 (2017)1. - ISSN 1746-4269
    Entomophagy - Ethno-entomology - Ethno-medicine - Folklore - Religion - Superstition - Termite mounds - Witchcraft
    Background: The number of termite species in the world is more than 2500, and Africa with more than 1000 species has the richest intercontinental diversity. The family Termitidae contains builders of great mounds up to 5 m high. Colonies are composed of casts: a queen, a king, soldiers and workers. Some species of termite cultivate specialised fungi to digest cellulose. Termites constitute 10% of all animal biomass in the tropics. The purpose of the study was to make an overview of how termites are utilized, perceived and experienced in daily life across sub-Saharan Africa. Method: Ethno-entomological information on termites (Isoptera) in sub-Saharan Africa was collected by: (1) interviews with more than 300 people from about 120 ethnic groups from 27 countries in the region; (2) library studies in Africa, London, Paris and Leiden. Results: Vernacular names relate to mounds, insects as food, the swarming, and the behaviour of termites. Swarming reproductive, soldiers and queens are collected as food. There are many different ways to harvest them. Termites can also be used as feed for poultry or as bait to catch birds and fish. The mushrooms that grow each year from the fungus gardens on the termite mounds are eaten. The soldiers, the fungus gardens and the soil of termite mounds are used for multiple medicinal purposes. Mounds and soil of termites have numerous functions: for geochemical prospecting, making bricks, plastering houses, making pots, and for storage. Termite soil is often used as fertilizer. The act of eating soil (geophagy) among women, especially those that are pregnant, is practised all over Africa. The mounds can serve as burying places and are often associated with the spiritual world, especially containing the spirits of ancestors. Termites also play a role as oracle, in superstitious beliefs, in art and literature. Conclusion: The following characteristics make termites so appealing: the dominance in the landscape, the social organization, the destructive power, and the provision of food. The study shows that termites play a major role in peoples' lives, in physical as well as spiritual aspects.
    Data from: Plant mutualisms with rhizosphere microbiota in introduced versus native ranges
    Shelby, Natasha ; Duncan, Richard P. ; Putten, W.H. van der; Mcginn, Kevin J. ; Weser, Carolin ; Hulme, Philip E. - \ 2016
    Wageningen University & Research
    Plant–soil (below-ground) interactions - alien - arbuscular mycorrhizal fungi (AMF) - invasive - non-native - parasitism - rhizobia - root fungal symbiont (RFS)
    The performance of introduced plants can be limited by the availability of soil mutualists outside their native range, but how interactions with mutualists differ between ranges is largely unknown. If mutualists are absent, incompatible or parasitic, plants may compensate by investing more in root biomass, adapting to be more selective or by maximizing the benefits associated with the mutualists available. We tested these hypotheses using seven non-agricultural species of Trifolium naturalized in New Zealand (NZ). We grew seeds from two native (Spain, UK) and one introduced (NZ) provenance of each species in glasshouse pots inoculated with rhizosphere microbiota collected from conspecifics in each region. We compared how plant biomass, degree of colonization by rhizobia and arbuscular mycorrhizal fungi (AMF), and the growth benefit associated with each mutualist differed between provenances (native and introduced populations) when grown with soil microbiota from each region. We also tested whether the growth benefit of colonization by mutualists was correlated with the extent to which alien plants were distributed in the introduced range. Rhizobia colonization was generally lower among introduced relative to native provenances. In NZ soils, 9% of all plants lacked rhizobia and 16% hosted parasitic nodules, whereas in native-range soils, there was no evidence of parasitism and all but one plant hosted rhizobia. Growth rates as a factor of rhizobia colonization were always highest when plants were grown in soil from their home range. Colonization by AMF was similar for all provenances in all soils but for four out of seven species grown in NZ soils, the level of AMF colonization was negatively correlated with growth rate. In general, introduced provenances did not compensate for lower growth rates or lower mutualist associations by decreasing shoot–root ratios. Synthesis. Despite differences between introduced and native provenances in their associations with soil mutualists and substantial evidence of parasitism in the introduced range, neither level of colonization by mutualists nor the growth benefit associated with colonization was correlated with the extent of species’ distributions in the introduced range, suggesting mutualist associations are not predictive of invasion success for these species.
    No difference in the competitive ability of introduced and native Trifolium provenances when grown with soil biota from their introduced and native ranges
    Shelby, Natasha ; Hulme, P.E. ; Putten, W.H. van der; McGinn, Kevin J. ; Weser, Carolin ; Duncan, R.P. - \ 2016
    AoB Plants 8 (2016). - ISSN 2041-2851
    The evolution of increased competitive ability (EICA) hypothesis could explain why some introduced plant species perform better outside their native ranges. EICA proposes that introduced plants escape specialist pathogens or herbivores leading to selection for resources to be reallocated away from defence and toward greater competitive ability. We tested the hypothesis that escape from soil enemies has led to increased competitive ability in three non-agricultural Trifolium (Fabaceae) species native to Europe that were introduced to New Zealand in the 19th century. Trifolium performance is intimately tied to rhizosphere biota. Thus, we grew plants from one introduced (New Zealand) and two native (Spain and the UK) provenances for each of three species in pots inoculated with soil microbiota collected from the rhizosphere beneath conspecifics in the introduced and native ranges. Plants were grown singly and in competition with conspecifics from a different provenance in order to compare competitive ability in the presence of different microbial communities. In contrast to the predictions of the EICA hypothesis, we found no difference in the competitive ability of introduced and native provenances when grown with soil microbiota from either the native or introduced range. Although plants from introduced provenances of two species grew more slowly than native provenances in native-range soils, as predicted by the EICA hypothesis, plants from the introduced provenance were no less competitive than native conspecifics. Overall, the growth rates of plants grown singly was a poor predictor of their competitive ability, highlighting the importance of directly quantifying plant performance in competitive scenarios, rather than relying on surrogate measures such as growth rate.
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