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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    Intensive measurements of gas, water, and energy exchange between vegetation and troposhere during the MONTES campaign in a vegetation gradient from short semi-desertic shrublands to tall wet temperate forests in the NW Mediterranean Basin
    Penuelas, J. ; Guenther, A. ; Rapparini, F. ; Llusia, J. ; Vilà-Guerau De Arellano, J. - \ 2013
    Atmospheric Environment 75 (2013). - ISSN 1352-2310 - p. 348 - 364.
    volatile organic-compounds - tethered balloon measurements - atmospheric boundary-layer - isoprene emission - quercus-ilex - biogenic emissions - particle formation - pinus-halepensis - field conditions - barcelona area
    MONTES (“Woodlands”) was a multidisciplinary international field campaign aimed at measuring energy, water and especially gas exchange between vegetation and atmosphere in a gradient from short semi-desertic shrublands to tall wet temperate forests in NE Spain in the North Western Mediterranean Basin (WMB). The measurements were performed at a semidesertic area (Monegros), at a coastal Mediterranean shrubland area (Garraf), at a typical Mediterranean holm oak forest area (Prades) and at a wet temperate beech forest (Montseny) during spring (April 2010) under optimal plant physiological conditions in driest-warmest sites and during summer (July 2010) with drought and heat stresses in the driest–warmest sites and optimal conditions in the wettest–coolest site. The objective of this campaign was to study the differences in gas, water and energy exchange occurring at different vegetation coverages and biomasses. Particular attention was devoted to quantitatively understand the exchange of biogenic volatile organic compounds (BVOCs) because of their biological and environmental effects in the WMB. A wide range of instruments (GC–MS, PTR-MS, meteorological sensors, O3 monitors,…) and vertical platforms such as masts, tethered balloons and aircraft were used to characterize the gas, water and energy exchange at increasing footprint areas by measuring vertical profiles. In this paper we provide an overview of the MONTES campaign: the objectives, the characterization of the biomass and gas, water and energy exchange in the 4 sites-areas using satellite data, the estimation of isoprene and monoterpene emissions using MEGAN model, the measurements performed and the first results. The isoprene and monoterpene emission rates estimated with MEGAN and emission factors measured at the foliar level for the dominant species ranged from about 0 to 0.2 mg m-2 h-1 in April. The warmer temperature in July resulted in higher model estimates from about 0 to ca. 1.6 mg m-2 h-1 for isoprene and ca. 4.5 mg m-2 h-1 for monoterpenes, depending on the site vegetation and footprint area considered. There were clear daily and seasonal patterns with higher emission rates and mixing ratios at midday and summer relative to early morning and early spring. There was a significant trend in CO2 fixation (from 1 to 10 mg C m-2 d-1), transpiration (from 1–5 kg C m-2 d-1), and sensible and latent heat from the warmest–driest to the coolest–wettest site. The results showed the strong land-cover-specific influence on emissions of BVOCs, gas, energy and water exchange, and therefore demonstrate the potential for feed-back to atmospheric chemistry and climate
    Genomic and environmental selection patterns in two distinct lettuce crop-wild hybrid crosses
    Hartman, Y. ; Uwimana, B. ; Hooftman, D.A.P. ; Schranz, M.E. ; Wiel, C.C.M. van de; Smulders, M.J.M. ; Visser, R.G.F. ; Tienderen, P.H. van - \ 2013
    Evolutionary Applications 6 (2013)4. - ISSN 1752-4563 - p. 569 - 584.
    quantitative trait loci - rape brassica-napus - lactuca-sativa l. - avena-barbata - transgressive segregation - field conditions - domestication traits - hybridization - fitness - introgression
    Genomic selection patterns and hybrid performance influence the chance that crop (trans)genes can spread to wild relatives. We measured fitness(-related) traits in two different field environments employing two different crop–wild crosses of lettuce. We performed quantitative trait loci (QTL) analyses and estimated the fitness distribution of early- and late-generation hybrids. We detected consistent results across field sites and crosses for a fitness QTL at linkage group 7, where a selective advantage was conferred by the wild allele. Two fitness QTL were detected on linkage group 5 and 6, which were unique to one of the crop–wild crosses. Average hybrid fitness was lower than the fitness of the wild parent, but several hybrid lineages outperformed the wild parent, especially in a novel habitat for the wild type. In early-generation hybrids, this may partly be due to heterosis effects, whereas in late-generation hybrids transgressive segregation played a major role. The study of genomic selection patterns can identify crop genomic regions under negative selection across multiple environments and cultivar–wild crosses that might be applicable in transgene mitigation strategies. At the same time, results were cultivar-specific, so that a case-by-case environmental risk assessment is still necessary, decreasing its general applicability.
    Hybridization between crops and wild relatives: the contribution of cultivated lettuce to the vigour of crop-wild hybrids under drought, salinity and nutrient deficiency conditions
    Uwimana, B. ; Smulders, M.J.M. ; Hooftman, D.A.P. ; Hartman, Y. ; Tienderen, P.H. van; Jansen, J. ; McHale, L.K. ; Michelmore, R.W. ; Wiel, C.C.M. van de; Visser, R.G.F. - \ 2012
    Theoretical and Applied Genetics 125 (2012)6. - ISSN 0040-5752 - p. 1097 - 1111.
    quantitative trait loci - genetically-engineered organisms - lactuca-sativa l. - gene flow - helianthus-paradoxus - sunflower hybrids - vegetative growth - transgenic plants - field conditions - brassica-napus
    With the development of transgenic crop varieties, crop–wild hybridization has received considerable consideration with regard to the potential of transgenes to be transferred to wild species. Although many studies have shown that crops can hybridize with their wild relatives and that the resulting hybrids may show improved fitness over the wild parents, little is still known on the genetic contribution of the crop parent to the performance of the hybrids. In this study, we investigated the vigour of lettuce hybrids using 98 F2:3 families from a cross between cultivated lettuce and its wild relative Lactuca serriola under non-stress conditions and under drought, salinity and nutrient deficiency. Using single nucleotide polymorphism markers, we mapped quantitative trait loci associated with plant vigour in the F2:3 families and determined the allelic contribution of the two parents. Seventeen QTLs (quantitative trait loci) associated with vigour and six QTLs associated with the accumulation of ions (Na+, Cl- and K+) were mapped on the nine linkage groups of lettuce. Seven of the vigour QTLs had a positive effect from the crop allele and six had a positive effect from the wild allele across treatments, and four QTLs had a positive effect from the crop allele in one treatment and from the wild allele in another treatment. Based on the allelic effect of the QTLs and their location on the genetic map, we could suggest genomic locations where transgene integration should be avoided when aiming at the mitigation of its persistence once crop–wild hybridization takes place
    Crop to wild introgression in lettuce: following the fate of crop genome segments in backcross populations
    Uwimana, B. ; Smulders, M.J.M. ; Hooftman, D.A.P. ; Hartman, Y. ; Tienderen, P.H. van; Jansen, J. ; McHale, L.K. ; Michelmore, R. ; Visser, R.G.F. ; Wiel, C.C.M. van de - \ 2012
    BMC Plant Biology 12 (2012). - ISSN 1471-2229
    quantitative trait loci - genetically-engineered organisms - gene flow - qtl analysis - lycopersicon-esculentum - domestication traits - helianthus-paradoxus - sunflower hybrids - field conditions - mixed models
    After crop-wild hybridization, some of the crop genomic segments may become established in wild populations through selfing of the hybrids or through backcrosses to the wild parent. This constitutes a possible route through which crop (trans)genes could become established in natural populations. The likelihood of introgression of transgenes will not only be determined by fitness effects from the transgene itself but also by the crop genes linked to it. Although lettuce is generally regarded as self-pollinating, outbreeding does occur at a low frequency. Backcrossing to wild lettuce is a likely pathway to introgression along with selfing, due to the high frequency of wild individuals relative to the rarely occurring crop-wild hybrids. To test the effect of backcrossing on the vigour of inter-specific hybrids, Lactuca serriola, the closest wild relative of cultivated lettuce, was crossed with L. sativa and the F1 hybrid was backcrossed to L. serriola to generate BC1 and BC2 populations. Experiments were conducted on progeny from selfed plants of the backcrossing families (BC1S1 and BC2S1). Plant vigour of these two backcrossing populations was determined in the greenhouse under non-stress and abiotic stress conditions (salinity, drought, and nutrient deficiency). Results Despite the decreasing contribution of crop genomic blocks in the backcross populations, the BC1S1 and BC2S1 hybrids were characterized by a substantial genetic variation under both non-stress and stress conditions. Hybrids were identified that performed equally or better than the wild genotypes, indicating that two backcrossing events did not eliminate the effect of the crop genomic segments that contributed to the vigour of the BC1 and BC2 hybrids. QTLs for plant vigour under non-stress and the various stress conditions were detected in the two populations with positive as well as negative effects from the crop. Conclusion As it was shown that the crop contributed QTLs with either a positive or a negative effect on plant vigour, we hypothesize that genomic regions exist where transgenes could preferentially be located in order to mitigate their persistence in natural populations through genetic hitchhiking.
    Genomic regions in crop-wild hybrids of Lettuce are affected differrently in different environments: implications for crop breeding
    Hartman, Y. ; Hooftman, D.A.P. ; Uwimana, B. ; Wiel, C.C.M. van de; Smulders, M.J.M. ; Visser, R.G.F. ; Tienderen, P.H. van - \ 2012
    Evolutionary Applications 5 (2012)6. - ISSN 1752-4563 - p. 629 - 640.
    quantitative trait loci - lactuca-serriola asteraceae - genetically-modified crops - avena-barbata - arabidopsis-thaliana - field conditions - natural environments - domestication traits - population-genetics - tandem constructs
    Many crops contain domestication genes that are generally considered to lower fitness of crop–wild hybrids in the wild environment. Transgenes placed in close linkage with such genes would be less likely to spread into a wild population. Therefore, for environmental risk assessment of GM crops, it is important to know whether genomic regions with such genes exist, and how they affect fitness. We performed quantitative trait loci (QTL) analyses on fitness(-related) traits in two different field environments employing recombinant inbred lines from a cross between cultivated Lactuca sativa and its wild relative Lactuca serriola. We identified a region on linkage group 5 where the crop allele consistently conferred a selective advantage (increasing fitness to 212% and 214%), whereas on linkage group 7, a region conferred a selective disadvantage (reducing fitness to 26% and 5%), mainly through delaying flowering. The probability for a putative transgene spreading would therefore depend strongly on the insertion location. Comparison of these field results with greenhouse data from a previous study using the same lines showed considerable differences in QTL patterns. This indicates that care should be taken when extrapolating experiments from the greenhouse, and that the impact of domestication genes has to be assessed under field conditions.
    Assessing risks and benefits of floral supplements in conservation biological control
    Winkler, K. ; Wackers, F.L. ; Termorshuizen, A.J. ; Lenteren, J.C. van - \ 2010
    BioControl 55 (2010)6. - ISSN 1386-6141 - p. 719 - 727.
    diamondback moth - euphydryas-chalcedona - field conditions - honeydew sugars - nectar sources - lepidoptera - parasitoids - resources - oviposition - herbivores
    The use of flowering field margins is often proposed as a method to support biological control in agro-ecosystems. In addition to beneficial insects, many herbivores depend on floral food as well. The indiscriminate use of flowering species in field margins can therefore lead to higher pest numbers. Based on results from field observations and laboratory experiments we assessed risks as well as benefits associated with the provision of nectar plants in field margins, using Brussels sprouts as a model system. Results show that Brussels sprouts bordered by nectar plants suitable for the cabbage white Pieris rapae L., suffered higher infestation levels by this herbivore. In contrast, nectar plants providing accessible nectar for the diamondback moth Plutella xylostella L., did not raise densities of P. xylostella larvae in the Brassica crop. Margins with Anethum graveolens L., selected on the basis of its suitability as nectar plant for parasitoids, significantly increased the number of adult Diadegma semiclausum Hellen in the crop. This didn't translate into enhanced parasitism rates, as parasitism of P. xylostella by D. semiclausum exceeded 65 % in all treatments, irrespective of the plants in the field margin. Our findings emphasize the importance of taking a multitrophic approach when choosing flowering field margin plants for biocontrol or other ecosystem services
    Ammonia volatilization from crop residues and frozen green manure crops
    Ruijter, F.J. de; Huijsmans, J.F.M. ; Rutgers, B. - \ 2010
    Atmospheric Environment 44 (2010)28. - ISSN 1352-2310 - p. 3362 - 3368.
    field conditions - n mineralization - nitrogen - decomposition - soil - denitrification - atmosphere - emissions - weather - grass
    Agricultural systems can lose substantial amounts of nitrogen (N). To protect the environment, the European Union (EU) has adopted several directives that set goals to limit N losses. National Emission Ceilings (NEC) are prescribed in the NEC directive for nitrogen oxides and ammonia. Crop residues may contribute to ammonia volatilization, but sufficient information on their contribution to the national ammonia volatilization is lacking. Experiments were carried out with the aim to assess the ammonia volatilization of crop residues left on the soil surface or incorporated into the soil under the conditions met in practice in the Netherlands during late autumn and winter. Ammonia emission from residues of broccoli, leek, sugar beet, cut grass, fodder radish (fresh and frozen) and yellow mustard (frozen) was studied during two winter seasons using volatilization chambers. Residues were either placed on top of soil or mixed with soil. Mixing residues with soil gave insignificant ammonia volatilization, whereas volatilization was 5–16 percent of the N content of residues when placed on top of soil. Ammonia volatilization started after at least 4 days. Total ammonia volatilization was related to C/N-ratio and N concentration of the plant material. After 37 days, cumulative ammonia volatilization was negligible from plant material with N concentration below 2 percent, and was 10 percent of the N content of plant material with 4 percent N. These observations can be explained by decomposition of plant material by micro-organisms. After an initial built up of the microbial population, NH4+ that is not needed for their own growth is released and can easily emit as NH3 at the soil surface. The results of the experiments were used to estimate the contribution of crop residues to ammonia volatilization in the Netherlands. Crop residues of arable crops and residues of pasture topping may contribute more than 3 million kg NH3–N to the national ammonia volatilization of the Netherlands, being more than 3 percent of the national emissions in 2005. This contribution should therefore be considered when focusing on the national ceilings for ammonia emissions.
    Exploration of hitherto-uncultured bacteria from the rhizosphere
    Rocha, U.N. da; Overbeek, L.S. van; Elsas, J.D. van - \ 2009
    FEMS microbiology ecology 69 (2009)3. - ISSN 0168-6496 - p. 313 - 328.
    microbial community structure - soil bacteria - plant-growth - 16s rdna - marine bacterioplankton - phylum acidobacteria - chemical-processes - wheat rhizosphere - field conditions - analysis reveals
    The rhizosphere environment selects a particular microbial community that arises from the one present in bulk soil due to the release of particular compounds in exudates and different opportunities for microbial colonization. During plant-microorganism coevolution, microbial functions supporting plant health and productivity have developed, of which most are described in cultured plant-associated bacteria. This review discusses the state of the art concerning the ecology of the hitherto-uncultured bacteria of the rhizosphere environment, focusing on Acidobacteria, Verrucomicrobia and Planctomycetes. Furthermore, a strategy is proposed to recover bacterial isolates from these taxa from the rhizosphere environment.
    Nectar exploitation by herbivores and their parasitoids is a function of flower species and relative humidity
    Winkler, K. ; Wäckers, F.L. ; Kaufman, L.V. ; Larraz, V. ; Lenteren, J.C. van - \ 2009
    Biological Control 50 (2009)3. - ISSN 1049-9644 - p. 299 - 306.
    diadegma-insulare hymenoptera - diamondback moth lepidoptera - biological-control - nutritional state - floral resources - field conditions - honeydew sugars - aphid honeydew - longevity - ichneumonidae
    In conservation biological control, diversification of the agro ecosystem with flowering vegetation is seen as an important tool to support the broad range of predators and parasitoids that require nectar and pollen sources to survive and reproduce. In order to identify flowering plants that provide suitable food sources for natural enemies without supporting the pest species, we analyzed the exploitation of 19 flowering plants by two important lepidopteran cabbage pests, Pieris rapae and Plutella xylostella, and their hymenopteran parasitoids, Cotesia glomerata and Diadegma semiclausum. The experiments were conducted at 90% r.h., while Pieris rapae was tested both at 45% r.h. and at 90% r.h. At 45 ± 5% r.h., corresponding with field conditions at which P. rapae is predominantly active, the butterfly was unable to feed on a number of exposed floral nectar sources whose nectar was successfully exploited at 90% r.h. The broader nectar exploitation by P. rapae at the high humidity is presumably explained by the resulting decrease in nectar viscosity. When comparing D. semiclausum and its herbivorous host P. xylostella, the herbivore exploited a broader range of plants. However, those plants that benefited both the parasitoid and the herbivore had a much stronger effect on the longevity of the parasitoid. The results from the accessibility bioassay suggest that flowers where nectar is not accessible can have a negative impact on insect survival presumably by stimulating foraging without providing accessible nectar. Our results underline the importance of considering species-specific environmental conditions when fine-tuning the choice of nectar sources to be used in conservation biological control programs.
    Predicting the time to colonization of the parasitoid Diadegma semiclausum: the importance of the shape of spatial dispersal kernels for biological control
    Bianchi, F.J.J.A. ; Schellhorn, N.A. ; Werf, W. van der - \ 2009
    Biological Control 50 (2009)3. - ISSN 1049-9644 - p. 267 - 274.
    coccinella-septempunctata coleoptera - agricultural landscapes - pest-control - field conditions - populations - habitats - movement - systems - spread - biodiversity
    The time at which natural enemies colonize crop fields is an important determinant of their ability to suppress pest populations. This timing depends on the distance between source and sink habitats in the landscape. Here we estimate the time to colonization of sink habitats from a distant source habitat, using empirical mark-capture data of Diadegma semiclausum in Broccoli. The data originated from experiments conducted at two locations and dispersal was quantified by suction sampling before and after a major disturbance. Three dispersal kernels were fitted to the dispersal data: a normal, a negative exponential, and a square root negative exponential kernel. These kernels are characterized by a thin, intermediate and a fat tail, respectively. The dispersal kernels were included in an integro-difference equation model for parasitoid population redistribution to generate estimates of time to colonization of D. semiclausum in sink habitats at distances between 100 and 2000 m from a source. We show that the three dispersal kernels receive similar support from the data, but can produce a wide range of outcomes. The estimated arrival time of 1% of the D. semiclausum population at a distance 2000 m from the source ranges from 12 days to a length of time greatly exceeding the life span of the parasitoid. The square root negative exponential function, having the thickest tail among the tested functions, gave the fastest spread and colonization in three of the four data sets, but it gave the slowest redistribution in the fourth. In all four data sets, the rate of accumulation at the target increased with the mean dispersal distance of the fitted kernel model, irrespective of the fatness of the tail. This study underscores the importance of selecting a proper dispersal kernel for modelling spread and colonization time of organisms, and of the collection of pertinent data that enable kernel estimation and that can discriminate between different kernel shapes
    Impact of elevated carbon dioxide on the rhizosphere communities of Carex arenaria and Festuce rubra
    Drigo, B. ; Kowalchuk, G.A. ; Yergeau, E. ; Bezemer, T.M. ; Boschker, H.T.S. ; Veen, J.A. van - \ 2007
    Global Change Biology 13 (2007). - ISSN 1354-1013 - p. 2396 - 2410.
    arbuscular-mycorrhizal fungi - gradient gel-electrophoresis - atmospheric co2 enrichment - 16s ribosomal-rna - soil microbial communities - bacterial communities - biomass production - perennial grasses - trifolium-repens - field conditions
    The increase in atmospheric carbon dioxide (CO2) levels is predicted to stimulate plant carbon (C) fixation, potentially influencing the size, structure and function of micro- and mesofaunal communities inhabiting the rhizosphere. To assess the effects of increased atmospheric CO2 on bacterial, fungal and nematode communities in the rhizosphere, Carex arenaria (a nonmycorrhizal plant species) and Festuca rubra (a mycorrhizal plant species) were grown in three dune soils under controlled soil temperature and moisture conditions, while subjecting the aboveground compartment to defined atmospheric conditions differing in CO2 concentrations (350 and 700 ¿L L¿1). Real-time polymerase chain reaction (PCR) and PCR-denaturing gradient gel electrophoresis methods were used to examine effects on the size and structure of rhizosphere communities. Multivariate analysis of community profiles showed that bacteria were most affected by elevated CO2, and fungi and nematodes to a lesser extent. The influence of elevated CO2 was plant dependent, with the mycorrhizal plant (F. rubra) exerting a greater influence on bacterial and fungal communities. Biomarker data indicated that arbuscular mycorrhizal fungi (AMF) may play an important role in the observed soil community responses. Effects of elevated CO2 were also soil dependent, with greater influence observed in the more organic-rich soils, which also supported higher levels of AMF colonization. These results indicate that responses of soil-borne communities to elevated CO2 are different for bacteria, fungi and nematodes and dependent on the plant type and soil nutrient availability.
    Estimation of nitrogen losses via denitrification from a heavy clay soil under grass
    Salm, C. van der; Dolfing, J. ; Heinen, M. ; Velthof, G.L. - \ 2007
    Agriculture, Ecosystems and Environment 119 (2007)3-4. - ISSN 0167-8809 - p. 311 - 319.
    ammonia volatilization - field conditions - nitric-oxide - acetylene - rates - netherlands - cattle - level - model - top
    Denitrification is an important pathway for nitrogen (N) loss from agricultural soils, but measured field data on denitrification in clay soils are scarce. The objective of the present research was to obtain and compare three different approaches to estimate the annual N loss via denitrification from a heavy clay soil. Using the acetylene inhibition technique we measured denitrification monthly at 20 °C in intact soil cores of a clay soil under intensively managed grass over a period of 2 years. This approach resulted in estimates of N loss via denitrification of 127 kg N ha-1 year-1 in 2003 and 143 kg N ha-1 year-1 in 2004. We also measured potential denitrification. These data were used in combination with independently calibrated 'reduction functions' to correct for suboptimal soil nitrate contents, water filled pore space or soil temperature. This approach resulted in estimates of 143 and 325 kg N ha-1 year-1 for 2003 and 2004, respectively. These measurements furthermore indicated that 75% of the denitrification occurred in the upper 20 cm of the soil. Estimates of denitrification based on field balances, including measurements of leaching losses to ground and surface waters, were 152 kg N ha-1 year-1 for 2003 and 5 kg N ha-1 year-1 for 2004, when storage of nitrogen was assumed negligible. While all three different estimation methods have considerable uncertainty, they invariably lead to the conclusion that N losses via denitrification in this intensively managed clay soil are high (more than 79 kg N ha-1 year-1). Measurement of the actual denitrification gave the most consistent and least uncertain estimates and accordingly we concluded that direct measurement of the actual denitrification should be preferred despite it's theoretical shortcomings. This implies that about 25% of the N applied to the field as fertilizer and manure is lost to the environment. In this heavy clay soil 90% of this loss proceeds via denitrification, and 10% proceeds via leaching and drainage.
    Olfactory learning by predatory arthropods
    Boer, J.G. de; Dicke, M. - \ 2006
    Animal Biology 56 (2006)2. - ISSN 1570-7555 - p. 143 - 155.
    induced plant volatiles - methyl salicylate - field conditions - phytoseiulus-persimilis - cognitive architecture - carnivorous arthropods - beneficial insects - mites learn - prey - experience
    Many natural enemies of herbivorous arthropods can use herbivore-induced plant volatiles to locate their prey. The composition of herbivore-induced volatile blends is highly variable, e.g., for different plant or herbivore species. When this variation is predictable during the lifetime of an individual, learning is expected to be adaptive for natural enemies that use such information. Learning has indeed been demonstrated many times for parasitoid wasps that use herbivore-induced plant volatiles to locate their hosts. However, evidence for learning of plant volatiles by predatory mites and insects is scarce and this is the topic of the present paper. We first review previously published research that demonstrated that anthocorid bugs and the predatory mite Phytoseiulus persimilis have the capacity to learn. Next, we present new evidence for an effect of previous experiences of P. persimilis on its responses to mixtures of volatile blends, induced by prey or non-prey herbivores. Finally, we discuss the ecological relevance of olfactory learning by predatory arthropods and the need to address this topic in future research
    Nematode Indicators of Organic Enrichment
    Ferris, H. ; Bongers, A.M.T. - \ 2006
    Journal of Nematology 38 (2006)1. - ISSN 0022-300X - p. 3 - 12.
    bacterial-feeding nematodes - population energetics - atmospheric co2 - food-web - species composition - field conditions - faunal analysis - maturity index - spatial scales - soil
    The organisms of the soil food web, dependent on resources from plants or on amendment from other sources, respond characteristically to enrichment of their environment by organic matter. Primary consumers of the incoming substrate, including bacteria, fungi, plant-feeding nematodes, annelids, and some microarthropods, are entry-level indicators of enrichment. However, the quantification of abundance and biomass of this diverse group, as an indicator of resource status, requires a plethora of extraction and assessment techniques. Soluble organic compounds are absorbed by bacteria and fungi, while fungi also degrade more recalcitrant sources. These organisms are potential indicators of the nature of incoming substrate, but current methods of biomass determination do not reliably indicate their community composition. Guilds of nematodes that feed on bacteria (e.g., Rhabditidae, Panagrolaimidae) and fungi (e.g., Aphelenchidae, Aphelenchoididae) are responsive to changes in abundance of their food. Through direct herbivory, plant-feeding nematodes (e.g., many species of Tylenchina) also contribute to food web resources. Thus, analysis of the nematode community of a single sample provides indication of carbon flow through an important herbivore channel and through channels mediated by bacteria and fungi. Some nematode guilds are more responsive than others to resource enrichment. Generally, those bacterivores with short life-cycles and high reproductive potential (e.g., Rhabditidae) most closely mirror the bloom of bacteria or respond most rapidly to active plant growth. The feeding habits of some groups remain unclear. For example, nematodes of the Tylenchidae may constitute 30% or more of the individuals in a soil sample; further study is necessary to determine which resource channels they portray and the appropriate level of taxonomic resolution for this group. A graphic representation of the relative biomass of bacterivorous, fungivorous, and herbivorous nematodes provides a useful tool for assessing the importance of the bacterial, fungal, and plant resource channels in an extant food web
    Exposure of Lima bean leaves to volatiles from herbivore-induced conspecific plants results in emission of carnivore attractants: active or passive process?
    Choh, Y. ; Shimoda, T. ; Ozawa, R. ; Dicke, M. ; Takabayashi, J. - \ 2004
    Journal of Chemical Ecology 30 (2004)7. - ISSN 0098-0331 - p. 1305 - 1317.
    tetranychus-urticae - field conditions - natural enemies - jasmonic acid - spider-mites - attack - phytoseiidae - responses - mutualism - predator
    There is increasing evidence that volatiles emitted by herbivore-damaged plants can cause responses in downwind undamaged neighboring plants, such as the attraction of carnivorous enemies of herbivores. One of the open questions is whether this involves an active (production of volatiles) or passive (adsorption of volatiles) response of the uninfested downwind plant. This issue is addressed in the present study. Uninfested lima bean leaves that were exposed to volatiles from conspecific leaves infested with the spider mite Tetranychus urticae, emitted very similar blends of volatiles to those emitted from infested leaves themselves. Treating leaves with a protein-synthesis inhibitor prior to infesting them with spider mites completely suppressed the production of herbivore-induced volatiles in the infested leaves. Conversely, inhibitor treatment to uninfested leaves prior to exposure to volatiles from infested leaves did not affect the emission of volatiles from the exposed, uninfested leaves. This evidence supports the hypothesis that response of the exposed downwind plant is passive. T. urticae-infested leaves that had been previously exposed to volatiles from infested leaves emitted more herbivore-induced volatiles than T. urticae-infested leaves previously exposed to volatiles from uninfested leaves. The former leaves were also more attractive to the predatory mite, Phytoseiulus persimilis, than the latter. This shows that previous exposure of plants to volatiles from herbivore-infested neighbors results in a stronger response of plants in terms of predator attraction when herbivores damage the plant. This supports the hypothesis that the downwind uninfested plant is actively involved. Both adsorption and production of volatiles can mediate the attraction of carnivorous mites to plants that have been exposed to volatiles from infested neighbors.
    Competition effects for copper between soil, soil solution and yeast in a bio assay for Folsomia candida willem
    Zee, S.E.A.T.M. van der; Temminghoff, E.J.M. ; Marinussen, M.P.J.C. - \ 2004
    Environmental Toxicology and Chemistry 23 (2004)7. - ISSN 0730-7268 - p. 1743 - 1750.
    contaminated sandy soil - dissolved organic-matter - saccharomyces-cerevisiae - lumbricus-rubellus - field conditions - heavy-metals - ph - earthworm - toxicity - bioavailability
    We investigated the accumulation of copper (Cu) by the springtail Folsomia candida Willem, if exposed to Cu-contaminated sandy soil with yeast as a food source. Commonly, the dissolved and the easily desorbed Cu fractions are assumed to be available for uptake, and as both fractions depend on pH, a pH dependency of copper uptake and accumulation is expected. In recent studies with springtails this dependency was not observed. To explain this, we show that both the adsorption of copper by yeast and by soil is indeed pH dependent; however, these dependencies differ. Addition of yeast as a food source to copper-contaminated soil leads to competition for copper by yeast and soil that suppresses the pH dependency of copper adsorption by yeast. This may cause a pH dependency not to be observed in copper accumulation by springtails if they predominantly feed on yeast in bioassays. We conclude that the addition of artificial food sources in bioassays may affect the cause-effect relationships that are investigated. A combination of (soil) chemical experimentation and modeling and ecotoxicological studies may help in identifying such bias and, therefore, with interpreting bioassays.
    Lima bean leaves exposed to herbivore-induced conspecific plant volatiles attract herbivores in addition to carnivores
    Horiuchi, J.I. ; Arimura, G.I. ; Ozawa, R. ; Shimoda, T. ; Dicke, M. ; Takabayashi, J. ; Nishioka, T. - \ 2003
    Applied Entomology and Zoology 38 (2003)3. - ISSN 0003-6862 - p. 365 - 368.
    tetranychus-urticae - induced resistance - field conditions - wild tobacco - spider-mites - communication - sagebrush - responses - predator - defense
    We tested the response of the herbivorous mite Tetranychus urticae to uninfested lima bean leaves exposed to herbivore-induced conspecific plant volatiles by using a Y-tube olfactometer. First, we confirmed that exposed uninfested leaves next to infested leaves were more attractive to carnivorous mites Phytoseiulus persimilis than uninfested leaves next to uninfested conspecific leaves. Under the same conditions, uninfested leaves next to infested conspecific leaves were more attractive to T urticae than uninfested leaves next to uninfested leaves. Based on these data, we discuss the role of the volatiles from the exposed plants in a tritrophic system.
    Mixed blends of herbivore-induced plant volatiles and foraging succes of carnivorous arthropods
    Dicke, M. ; Boer, J.G. de; Höfte, M. ; Rocha-Granados, C. - \ 2003
    Oikos 101 (2003)1. - ISSN 0030-1299 - p. 38 - 48.
    parasitoids cotesia-glomerata - tritrophic interaction webs - predatory mites - natural enemies - phytoseiulus-persimilis - field conditions - cabbage plants - host-plant - ecology - infochemicals
    Food webs are overlaid with infochemical webs that mediate direct and indirect interactions. Behavioural ecologists have extensively documented that carnivorous arthropods exploit herbivore-induced plant volatiles during foraging for herbivorous arthropods. Most studies on the role of infochemicals in multitrophic interactions have been conducted against an odour-free background, although field studies show that carnivores also use herbivore-induced plant volatiles under more complex conditions. Here we investigated the effect of mixing the blends of volatiles emitted by two plant species on the foraging behaviour of the predatory mite Phytoseiulus persimilis. This was done in an olfactometer under laboratory conditions and in a semi-field setup under greenhouse conditions. The olfactometer setup ensured directed mixing of the two odour blends, while odour mixing in the greenhouse setup was much less controlled and resulted from diffusion. In 4 out of 5 olfactometer experiments the behaviour towards volatiles from spider-mite (Tetranychus urticae) infested Lima bean plants was not affected by mixing with volatiles from caterpillar (Pieris brassicae) infested Brussels sprouts plants. In the fifth olfactometer experiment the response shifted significantly towards the volatiles from infested Lima bean leaves without volatiles from infested cabbage leaves. In the greenhouse setup no effect of infested cabbage plants or their volatiles on the location of spider-mite infested bean plants was recorded. The two odour blends used in this study, i.e. those from spider-mite infested Lima bean leaves and from caterpillar-infested Brussels sprouts plants, are very different and there is no overlap in compounds that are known to attract the predators. The results are discussed in the context of other types of odour-blend mixing and the effects on food web interactions.
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