IMPACT4SOIL OpenAire Datacite Research@WUR KNAW Pure Open Access 2016-11-29 Open Access1. The diversity of the surrounding plant community can directly affect the abundance of insects on a focal plant as well as the size and quality of that focal plant. However, to what extent the effects of plant diversity on the arthropod community on a focal plant are mediated by host plant quality or by the diversity of the surrounding plants remains unresolved. 2. In the field, we sampled arthropod communities on focal Jacobaea vulgaris plants growing in experimental plant communities that were maintained at different levels of diversity (1, 2, 4 or 9 species) for three years. Focal plants were also planted in plots without surrounding vegetation. We recorded the structural characteristics of each of the surrounding plant communities as well as the growth, and primary and secondary chemistry (pyrrolizidine alkaloids, PAs) of the focal plants to disentangle the potential mechanisms causing the diversity effects. 3. Two years after planting, the abundance of arthropods on focal plants that were still in the vegetative stage decreased with increasing plant diversity, while the abundance of arthropods on reproductive focal plants was not significantly affected by the diversity of the neighbouring community. The size of both vegetative and reproductive focal plants was not significantly affected by the diversity of the neighbouring community, but the levels of PAs and the foliar N concentration of vegetative focal plants decreased with increasing plant diversity. Structural equation modelling revealed that the effects of plant diversity on the arthropod communities on focal plants were not mediated by changes in plant quality. 4. Synthesis. Plant quality can greatly influence insect preference and performance. However, under natural conditions the effects of the neighbouring plant community can overrule the plant quality effects of individual plants growing in those communities on the abundance of insects associated to this plant. Open Access1. The diversity of the surrounding plant community can directly affect the abundance of insects on a focal plant as well as the size and quality of that focal plant. However, to what extent the effects of plant diversity on the arthropod community on a focal plant are mediated by host plant quality or by the diversity of the surrounding plants remains unresolved. 2. In the field, we sampled arthropod communities on focal Jacobaea vulgaris plants growing in experimental plant communities that were maintained at different levels of diversity (1, 2, 4 or 9 species) for three years. Focal plants were also planted in plots without surrounding vegetation. We recorded the structural characteristics of each of the surrounding plant communities as well as the growth, and primary and secondary chemistry (pyrrolizidine alkaloids, PAs) of the focal plants to disentangle the potential mechanisms causing the diversity effects. 3. Two years after planting, the abundance of arthropods on focal plants that were still in the vegetative stage decreased with increasing plant diversity, while the abundance of arthropods on reproductive focal plants was not significantly affected by the diversity of the neighbouring community. The size of both vegetative and reproductive focal plants was not significantly affected by the diversity of the neighbouring community, but the levels of PAs and the foliar N concentration of vegetative focal plants decreased with increasing plant diversity. Structural equation modelling revealed that the effects of plant diversity on the arthropod communities on focal plants were not mediated by changes in plant quality. 4. Synthesis. Plant quality can greatly influence insect preference and performance. However, under natural conditions the effects of the neighbouring plant community can overrule the plant quality effects of individual plants growing in those communities on the abundance of insects associated to this plant. Surrounding plant community and soil measurementsA detailed description of the field experiment is presented in the article. At the end of August 2011, plant community measurements were made in each plot, to estimate the structural complexity of the community. For each plant community, the percentage cover of plant species was recorded in two 1 m2 quadrants along a diagonal transect within each plot. The total percentage cover can exceed 100% because plants in a community can overlap. The height of the vegetation was measured using the vertical drop disc method (Stewart et al. 2001). The disc weighed 200 g, had a diameter of 300 mm, and was released from a 1.5-m height. The height was measured at 10 random locations within each plot. One week after plant sampling, soil cores of 15 cm depth and 2.5 cm diameter were collected from each experimental plot at five random positions. The soil samples were pooled per plot and used for chemical analysis. Mineral N content (NH4+ and NO3) in soil samples was determined colorimetrically in the CaCl2 extraction using a Traacs 800 autoanalyser (TechniCon Systems Inc, USA). The C:N-ratio in soil samples was measured on a FlashEA 1112 Series NC soil analyser (Thermo Scientific). pH was measured in 2:5 dry soil : water suspensions. The percentage organic C was determined according to Nelson and Sommers (1982) and available P according to Olsen et al. (1954) and measured at 720 nm.community and soil measurements.7zArthropod database 2011A detailed description of the field experiment is presented in the article. Arthropods at all stages of their development (eggs, immature and adults) on each Jacobaea vulgaris plant were collected on four occasions from May to August 2011. During each collection, all plants were carefully inspected between 10:00 am and 16:00 pm and all arthropods that were observed on a plant were collected using an aspirator by three collectors distributed evenly over the field. Each collector inspected all 1324 plants, spending an approximately equal amount of time at each plant at all diversity levels. All arthropods were stored individually in 70% ethanol in labelled Eppendorf tubes. Most arthropods were identified to species or family level. All arthropod species were assigned to feeding group (specialist herbivore, generalist herbivore, predator, pollinator, detritivore and omnivore) based on their feeding strategy and the degree of specialization.PA content J. vulgarisPA analysis of leaf and root samples was carried out using liquid chromatography-tandem mass spectrometry (LC-MS/MS) following the procedure outlined in Kostenko et al. (2013). In brief, 5 mg of freeze-dried ground plant material was extracted with 0.5 ml 2% formic acid solution containing heliotrine (1 µg•ml-1) as internal standard. After centrifugation and filtration, 25 µl of the extracted filtrate was diluted with 975 µl of 10 mM ammonium hydroxide solution and 10 µl was injected in a Waters Acquity ultra-performance chromatographic system coupled to a Waters Quattro Premier tandem mass spectrometer (Waters, Milford, MA, USA). Separation and mass spectrometric detection of the PAs was as described in Cheng et al. (2011) and Appendix S2. Data were processed using Masslynx 4.1 software.Jacobaea vulgaris_characteristics 2011A detailed description of the field experiment and plant measurements are presented in the article. Leaf carbon (C) and nitrogen (N) concentrations were determined using a Flash EA1112 CN analyser (Interscience, Breda, The Netherlands). Phytochemistry Jacobaea vulgaris plant–herbivore interactions plant quality insect community plant species richness Verwerkte data phytochemistry Processed data 15. Life on land plant-herbivore interactions biodiversity Kostenko, O., Mulder, P.P.J., Courbois, Matthijs, Bezemer, T.M., 2016-01-01 Open Access1. The diversity of the surrounding plant community can directly affect the abundance of insects on a focal plant as well as the size and quality of that focal plant. However, to what extent the effects of plant diversity on the arthropod community on a focal plant are mediated by host plant quality or by the diversity of the surrounding plants remains unresolved. 2. In the field, we sampled arthropod communities on focal Jacobaea vulgaris plants growing in experimental plant communities that were maintained at different levels of diversity (1, 2, 4 or 9 species) for three years. Focal plants were also planted in plots without surrounding vegetation. We recorded the structural characteristics of each of the surrounding plant communities as well as the growth, and primary and secondary chemistry (pyrrolizidine alkaloids, PAs) of the focal plants to disentangle the potential mechanisms causing the diversity effects. 3. Two years after planting, the abundance of arthropods on focal plants that were still in the vegetative stage decreased with increasing plant diversity, while the abundance of arthropods on reproductive focal plants was not significantly affected by the diversity of the neighbouring community. The size of both vegetative and reproductive focal plants was not significantly affected by the diversity of the neighbouring community, but the levels of PAs and the foliar N concentration of vegetative focal plants decreased with increasing plant diversity. Structural equation modelling revealed that the effects of plant diversity on the arthropod communities on focal plants were not mediated by changes in plant quality. 4. Synthesis. Plant quality can greatly influence insect preference and performance. However, under natural conditions the effects of the neighbouring plant community can overrule the plant quality effects of individual plants growing in those communities on the abundance of insects associated to this plant. Open Access1. The diversity of the surrounding plant community can directly affect the abundance of insects on a focal plant as well as the size and quality of that focal plant. However, to what extent the effects of plant diversity on the arthropod community on a focal plant are mediated by host plant quality or by the diversity of the surrounding plants remains unresolved. 2. In the field, we sampled arthropod communities on focal Jacobaea vulgaris plants growing in experimental plant communities that were maintained at different levels of diversity (1, 2, 4 or 9 species) for three years. Focal plants were also planted in plots without surrounding vegetation. We recorded the structural characteristics of each of the surrounding plant communities as well as the growth, and primary and secondary chemistry (pyrrolizidine alkaloids, PAs) of the focal plants to disentangle the potential mechanisms causing the diversity effects. 3. Two years after planting, the abundance of arthropods on focal plants that were still in the vegetative stage decreased with increasing plant diversity, while the abundance of arthropods on reproductive focal plants was not significantly affected by the diversity of the neighbouring community. The size of both vegetative and reproductive focal plants was not significantly affected by the diversity of the neighbouring community, but the levels of PAs and the foliar N concentration of vegetative focal plants decreased with increasing plant diversity. Structural equation modelling revealed that the effects of plant diversity on the arthropod communities on focal plants were not mediated by changes in plant quality. 4. Synthesis. Plant quality can greatly influence insect preference and performance. However, under natural conditions the effects of the neighbouring plant community can overrule the plant quality effects of individual plants growing in those communities on the abundance of insects associated to this plant. Surrounding plant community and soil measurementsA detailed description of the field experiment is presented in the article. At the end of August 2011, plant community measurements were made in each plot, to estimate the structural complexity of the community. For each plant community, the percentage cover of plant species was recorded in two 1 m2 quadrants along a diagonal transect within each plot. The total percentage cover can exceed 100% because plants in a community can overlap. The height of the vegetation was measured using the vertical drop disc method (Stewart et al. 2001). The disc weighed 200 g, had a diameter of 300 mm, and was released from a 1.5-m height. The height was measured at 10 random locations within each plot. One week after plant sampling, soil cores of 15 cm depth and 2.5 cm diameter were collected from each experimental plot at five random positions. The soil samples were pooled per plot and used for chemical analysis. Mineral N content (NH4+ and NO3) in soil samples was determined colorimetrically in the CaCl2 extraction using a Traacs 800 autoanalyser (TechniCon Systems Inc, USA). The C:N-ratio in soil samples was measured on a FlashEA 1112 Series NC soil analyser (Thermo Scientific). pH was measured in 2:5 dry soil : water suspensions. The percentage organic C was determined according to Nelson and Sommers (1982) and available P according to Olsen et al. (1954) and measured at 720 nm.community and soil measurements.7zArthropod database 2011A detailed description of the field experiment is presented in the article. Arthropods at all stages of their development (eggs, immature and adults) on each Jacobaea vulgaris plant were collected on four occasions from May to August 2011. During each collection, all plants were carefully inspected between 10:00 am and 16:00 pm and all arthropods that were observed on a plant were collected using an aspirator by three collectors distributed evenly over the field. Each collector inspected all 1324 plants, spending an approximately equal amount of time at each plant at all diversity levels. All arthropods were stored individually in 70% ethanol in labelled Eppendorf tubes. Most arthropods were identified to species or family level. All arthropod species were assigned to feeding group (specialist herbivore, generalist herbivore, predator, pollinator, detritivore and omnivore) based on their feeding strategy and the degree of specialization.PA content J. vulgarisPA analysis of leaf and root samples was carried out using liquid chromatography-tandem mass spectrometry (LC-MS/MS) following the procedure outlined in Kostenko et al. (2013). In brief, 5 mg of freeze-dried ground plant material was extracted with 0.5 ml 2% formic acid solution containing heliotrine (1 µg•ml-1) as internal standard. After centrifugation and filtration, 25 µl of the extracted filtrate was diluted with 975 µl of 10 mM ammonium hydroxide solution and 10 µl was injected in a Waters Acquity ultra-performance chromatographic system coupled to a Waters Quattro Premier tandem mass spectrometer (Waters, Milford, MA, USA). Separation and mass spectrometric detection of the PAs was as described in Cheng et al. (2011) and Appendix S2. Data were processed using Masslynx 4.1 software.Jacobaea vulgaris_characteristics 2011A detailed description of the field experiment and plant measurements are presented in the article. Leaf carbon (C) and nitrogen (N) concentrations were determined using a Flash EA1112 CN analyser (Interscience, Breda, The Netherlands). Data from: Effects of plant diversity on the concentration of secondary plant metabolites and the density of arthropods on focal plants in the field 10.5061/dryad.54ht3 dataset https://doi.org/10.5061/dryad.54ht3