Senecio Jacobaea Research Articles

Parallel evolution in an invasive plant: effect of herbivores on competitive ability and regrowth of Jacobaea vulgaris.

A shift in the composition of the herbivore guild in the invasive range is expected to select for plants with a higher competitive ability, a lower regrowth capacity and a lower investment in defence. We show here that parallel evolution took place in three geographically distinct invasive regions that differed significantly in climatic conditions. This makes it most likely that indeed the shifts in herbivore guilds were causal to the evolutionary changes. We studied competitive ability and regrowth of invasive and native Jacobaea vulgaris using an intraspecific competition set-up with and without herbivory. Without herbivores invasive genotypes have a higher competitive ability than native genotypes. The invasive genotypes were less preferred by the generalist Mamestra brassicae but more preferred by the specialist Tyria jacobaeae, consequently their competitive ability was significantly increased by the first and reduced by the latter. Invasive genotypes showed a lower regrowth ability in both herbivore treatments.

Characterization of Pyrrozilidine alkaloids in botanicals and dietary supplements by LC/QTOF MS

Pyrrolizidine alkaloids are known to be hepatotoxic and hepatocarcenogenic compounds that are found in common weeds that grow throughout Europe. Contamination of plants, such as Senecio jacobaea (ragwort), that contain these secondary metabolites is common in botanicals used as dietary supplements and may pose a health risk. In this work we show the LC/MS/MS determination of 25 pyrrolizidine alkaloids in both plants and dietary supplements. The accurate mass MS/MS of these compounds is presented and described. This characterization can be the basis of routine monitoring methods and determination of other toxic pyrrolizidine alkaloids in botanicals and dietary supplements.

Species‐specific plant–soil feedback effects on above‐ground plant–insect interactions

Summary Plant–soil feedback (PSF) effects on plant performance strongly depend on the plant species that conditioned the soil. Recent studies have shown that PSF can change above‐ground plant–insect interactions via soil‐mediated changes in plant quality, but whether these effects depend on species‐specific soil conditioning is unknown. We examined how PSF effects of several plant species influence above‐ground plant–aphid interactions. We grew ragwort (Jacobaea vulgaris) in field soil conditioned specifically by 10 plant species, belonging to three functional groups (grasses, forbs and legumes), in a multispecies mixture of the conditioned soils and in control (unconditioned) field soil. We measured plant biomass, concentrations of primary (amino acids) and secondary (pyrrolizidine alkaloids) metabolites in phloem exudates, and performance of the generalist aphid Brachycaudus cardui and the specialist Aphis jacobaeae. We observed that plant species, via species‐specific effects on soil fungal communities, exerted unique plant–soil effects on J. vulgaris biomass, amino acid concentrations in phloem exudates and aphid performance. The direction and magnitude of the species‐specific PSF effects on aphid performance differed between both aphid species. PSF effects on soil fungal communities, plant biomass and A. jacobaeae performance also differed between grasses, forbs and legumes, with soil conditioning by forbs resulting in lowest plant biomass and aphid performance. Synthesis. Our study provides novel evidence that PSF effects on above‐ground plant–insect interactions are highly species specific. Our results add a new dimension to the rapidly developing research fields of PSF and above‐below‐ground interactions, and highlights that these fields are tightly linked.

Enemies lost: parallel evolution in structural defense and tolerance to herbivory of invasive Jacobaea vulgaris

According to the Shifting Defense Hypothesis, invasive plants should trade-off their costly quantitative defense to cheaper qualitative defense and growth due to the lack of natural specialist enemies and the presence of generalist enemies in the introduced areas. Several studies showed that plant genotypes from the invasive areas had a better qualitative defense than genotypes from the native area but only a few studies have focused on the quantitative defenses and tolerance ability. We compared structural defenses, tolerance and growth between invasive and native plant populations from different continents using the model plant Jacobaea vulgaris. We examined several microscopical structure traits, toughness, amount of cell wall proteins, growth and root-shoot ratio, which is a proxy for tolerance. The results show that invasive Jacobaea vulgaris have thinner leaves, lower leaf mass area, lower leaf cell wall protein contents and a lower root-shoot ratio than native genotypes. It indicates that invasive genotypes have poorer structural defense and tolerance to herbivory but potentially higher growth compared to native genotypes. These findings are in line with the Evolution of Increased Competitive Ability hypothesis and Shifting Defense Hypothesis. We also show that the invasiveness of this species in three geographically separated regions is consistently associated with the loss of parts of its quantitative defense and tolerance ability. The simultaneous change in quantitative defense and tolerance of the same magnitude and direction in the three invasive regions can be explained by parallel evolution. We argue that such parallel evolution might be attributed to the absence of natural enemies rather than adaptation to local abiotic factors, since climate conditions among these three regions were different. Understanding such evolutionary changes helps to understand why plant species become invasive and might be important for biological control.

Plants poisonous to horses in Europe

SummaryPoisoning of horses by plants is a relatively common veterinary problem and may occur when the fresh plant is ingested in pasture or when the plant contaminates hay, silage and feed. In Europe, horses are particularly at risk of poisoning by Cynoglossum officinale (houndstongue), Datura stramonium (jimson weed), Hypericum perforatum (St. John's wort), Nerium oleander (oleander), Pteridium aquilinum (bracken fern), Robinia pseudoacacia (black locust), Senecio jacobaea (tansy ragwort), Taxus baccata (European yew) and Thuja occidentalis (white cedar). For each of these poisonous plants the information given in this review includes plant distribution, conditions of poisoning, toxic active principles and clinical signs.

Interspecific competition of early successional plant species in ex-arable fields as influenced by plant–soil feedback

Plant–soil feedback can affect plants that belong to the same (intraspecific feedback) or different species (interspecific feedback). However, little is known about how intra- and interspecific plant–soil feedbacks influence interspecific plant competition. Here, we used plants and soil from early-stage ex-arable fields to examine how intra- and interspecific plant–soil feedbacks affect the performance of 10 conditioning species and the focal species, Jacobaea vulgaris. Plants were grown alone and in competition in both conditioned and control soils. Overall, plant–soil feedback of the 10 plant species influenced the competitiveness of J. vulgaris more strongly than their own competitiveness. However, effects depended on species combination: competitiveness of J. vulgaris was significantly enhanced by interspecific plant–soil feedback from Anthoxanthum odoratum, Agrostis capillaris, and Trifolium dubium, and significantly decreased by interspecific feedback from Achillea millefolium. Intraspecific feedback from Taraxacum officinale and A. odoratum decreased their competitiveness with J. vulgaris. There was a positive relationship between the strength of interspecific feedback and competitiveness of J. vulgaris in conditioned soil. Multiple linear regression showed that the competitiveness of J. vulgaris in conditioned soil was determined by interspecific feedback and competitiveness of neighbour plants. The positive relationship between interspecific feedback and competitiveness in control soil suggests that the soil feedback effect of the competing species on J. vulgaris can build up quickly during competition. We conclude that the effect of plant–soil feedback on interspecific competition may be due to either legacy effects of plant species previously colonizing the soil, or immediate interspecific feedback of the competing plant species via the soil. Therefore, our results suggest that plant–soil feedback can influence interspecific plant competition through a multitude of intra- and interspecific plant–soil interactions both from predecessors, and from the currently competing plant species.

Растительность залежей центральной части музея-заповедника «Куликово поле» (Тульская область)

The museum-preserve «The Kulikovo Field» is situated in the northern part of the Central Russian Upland within the forest-steppe zone near its northern border. There are a lot of abandoned fields, most of them left fallow since 1990–2000 years; the exact age of the old fields is unknown. Using the Braun-Blanquet approach as well as the method of K. Kopecký and S. Hejný (Kopecký, Hejný, 1974; Kopecký, 1992), the classification of the old-field vegetation of the central part of the museum-preserve was carried out. One derivate community, 2 basal communities (one of them with two variants), 3 communities and one association with three variants have been identified. The derivate community Conyza canadensis­ [Artemisietea vulgaris/Stellarietea mediae] is dominated by annual and biennial ruderal species: Conyza canadensis, Lactuca serriola and Carduus acanthoides. The association Convolvulo arvensis–Elytrigietum repentis is heterogeneous both in its floristic and subdominant composition and it can be divided into 3 variants. The variant typica represents monodominant communities where Elytrigia repens prevails. The variant Lactuca serriola is characterized by high constancy of Conyza canadensis, Lactuca serriola and some other ruderal plants and it represents coenoses dominated by Elytrigia repens with subdominants such as Lactuca serriola, Senecio jacobaea and Pilosella spp., mainly P. bauhini. The variant Cichorium intybus is dominated by Elytrigia repens with a subdominant Cichorium intybus; some mesophilous meadow species are often present. Variants Melilotus officinalis and Sonchus arvensis of the basal communityElytrigia repens–Cichorium intybus [Artemisietea vulgaris] are dominated by Cichorium intybus, Poa angustifolia and Elytrigia repens, the first of them also by Melilotus officinalis, Artemisia absinthium, and the second by Carduus acanthoides and Calamagrostis epigeios. Unlike the foregoing syntaxa the basal community Elytrigia repens–Cichorium intybus [Artemisietea vulgaris] is characterized by relative high constancy of some species pertaining to the order Galietalia veri, namely Fragaria viridis, Galium verum, Potentilla argentea. These species and also Poa angustifolia are the first steppificated meadow plants that appear in the old field communities under investigation. The community Pilosella bauhini [Onopordion acanthii] is dominated by Pilosella spp., mainly by P. bauhini that sometimes replaced by some ruderal plants, e. g. Achillea nobilis or Cichorium intybus. The peculiarity of this community is the low constancy and abundance of Elytrigia repens. The species of the orders Galietalia veri and Arrhenatheretalia play much noticeable role in the other syntaxa mentioned below, so these syntaxa are between the natural and synanthropic vegetation. The community Leucanthemum vulgare–Galium mollugo [Onopordion acanthii/Molinio-Arrhenatheretea] is distinguished by high abundance and constancy of some mesophilous and xeromesophilous meadow plants (Leucanthemum vulgare, Galium mollugo, Phleum pratense etc.). The community Artemisia marschalliana [Onopordion acanthii/Galietalia veri] is dominated mostly by Leontodon hispidus and Pilosella spp.; its peculiarity is a relatively high constancy of species common in the local steppificated meadows. The basal community Poa angustifolia [Galietalia veri/Artemisietea vulgaris] represents monodominant communities where Poa angustifolia prevails. Annual, biennial and some perennial ruderal species are rare in this variant, unlike most of the syntaxa mentioned above. The common feature of the last three syntaxa is subdominance of Fragaria viridis. It is known that the floristic composition of communities is changed during an old-field succession: the percentage of annual and biennial species declines and that of species pertaining to the classes of natural vegetation increases (Bonet, Pausas, 2007; Yamalov et al., 2008; Pankratova, Gannibal, 2009). Using the life-form and phytosociological spectrum of the syntaxa analysis an attempt to evaluate succession status of the described communities was made (tab. 9, 10). Based upon the results of this analysis, it is possible to suggest that the derivate community Conyza canadensis [Artemisietea vulgaris/Stellarietea mediae] is the earliest stage one can find in the investigated old fields. The variants Lactuca serriola and typica of the association Convolvulo arvensis–Elytrigietum repentis and the community Pilosella bauhini [Onopordion acanthii] are the next in the series. It seems that Pilosella spp. (P. bauhini and probably some other species of this genus) outcompete the pioneer species of initial stages, like Elytrigia repens, in some cases. The basal community Poa angustifolia [Galietalia veri / Artemisietea vulgaris] seems to be the most advanced stage: the percentage of annuals and biennials is minimal, and that of species pertaining to the syntaxa of natural vegetation of the high ranks, especially to the order Galietalia veri, increases greatly. Species richness of the communities is minimal at the most early stage, which is the peculiarity of the old-field vegetation (Pankratova, Gannibal, 2009; Ovcharova, Yamalov, 2013). Similar phenomenon was also noticed at the succession stages where strong dominant (Elytrigia repens or Poa angustifolia) pre­vails, regardless of how much advanced these stages are, the fact mentioned earlier (Prach, 1985). Species richness attains maximum at those stages of succession where the communities are polydominant and contain both early- and late-successional species, that was also previously described (Meiners et al., 2007).

Disentangling above- and belowground neighbor effects on the growth, chemistry, and arthropod community on a focal plant.

Neighboring plants can influence arthropods on a focal plant, and this can result in associational resistance or associational susceptibility. These effects can be mediated by above- and belowground interactions between the neighbor and focal plant, but determining the relative contribution of the above- and belowground effects remains an open challenge. We performed a common garden experiment with a design that enabled us to disentangle the above- and belowground effects of five different plant species on the growth and chemistry of the focal plant ragwort (Jacobaea vulgaris), and the arthropod community associated with this plant. Aboveground effects of different neighboring plant species were more important for the growth and quality of J. vulgaris and for the arthropod abundance on this plant than belowground effects of neighbors. This remained true when only indirect neighbor effects (via affecting the biomass or quality of the focal plant) were considered. The aboveground neighbor effects on arthropod abundance on the focal plant were strongly negative. However, the magnitude of the effect depended on the identity of the neighboring species, and herbivore abundance on the focal plant was higher when surrounded by conspecific than when surrounded by heterospecific plants. We also observed interactions between above- and belowground neighbor effects, indicating that these effects may be nonadditive. We conclude that above- and belowground associational effects are not equally strong, and that neighbor effects on plant-arthropod interactions occur predominantly aboveground.

Origin and systematic position of Jacobaea vulgaris (Asteraceae) octoploids: genetic and morphological evidence

Five cytotypes have been reported for Jacobaea vulgaris (syn.: Senecio jacobaea); three of them with euploid (tetraploid, hexaploid, and octoploid; 2n = 40, 60, and 80) and one with aneuploid (2n = 32) chromosome numbers. Among them, only tetra- and octoploid cytotypes are regularly found, the other two are very rare. In this study we re-evaluated the origin and systematic position of J. vulgaris octoploids. DNA ploidy levels, morphological, and genetic (AFLP, amplified fragment length polymorphism) data were generated for 38 populations of J. vulgaris from Central and Eastern Europe, and adjacent parts of North-Western Europe. Genetic dataset was supplemented with 16 populations of five closely related species: J. alpina, J. aquatica, J. erratica, J. erucifolia, and J. subalpina. The octoploid cytotype of J. vulgaris, known thus far only from Pannonia and Ukrainian Podillya regions, has also been found on two Baltic islands, Oland and Gotland. AFLP analyses showed clear genetic differences between tetra- and octoploid cytotypes and revealed that all octoploid plants are most likely of autopolyploid origin. The AFLP data also indicate that octoploids form two separate allopatric and monophyletic lineages, one represented by Pannonian and Oland populations, and the other represented by the populations from Podillya and Gotland. The octoploids from Gotland correspond to the previously recognized subspecies J. vulgaris subsp. gotlandica. The octoploids distributed in Pannonia are described here as a new subspecies, J. vulgaris subsp. pannonica.

Plant–soil feedback effects on plant quality and performance of an aboveground herbivore interact with fertilisation

Plant–soil feedback (PSF) effects on plant performance can be influenced by the availability of nutrients in the soil. Recent studies have shown that PSF effects can also change aboveground plant–insect interactions via soil‐mediated changes in plant quality, but whether this is influenced by soil nutrient availability is unknown. We examined how fertilisation influences PSF effects on aboveground plant‐aphid interactions in ragwort Jacobaea vulgaris. We grew J. vulgaris in soil conditioned by conspecific plants and in unconditioned soil at two levels of fertilisation and measured soil fungal communities, plant biomass, concentrations of primary (amino acids) and secondary (pyrrolizidine alkaloids; PAs) metabolites in phloem exudates, performance of the specialist aphid Aphis jacobaeae and sequestration of PAs by the aphid. We observed a strong interaction between soil conditioning and fertilisation on amino acid and PA concentrations in phloem exudates of J. vulgaris and on aphid performance, with opposite effects of soil conditioning at the two fertilisation levels. Plant biomass was reduced by soil conditioning and increased by fertilisation. Aphids contained high PA concentrations, converted N‐oxides into tertiary amines and preferentially sequestered certain PA compounds, but PA sequestration was not affected by any of the treatments. We conclude that effects of PSF and fertilisation on plant chemistry and aphid performance are interdependent. Our study highlights the need to consider the importance of abiotic soil conditions on the outcome of PSF effects on aboveground plant–insect interactions.

Toxicity of pyrrolizidine alkaloids to Spodoptera exigua using insect cell lines and injection bioassays.

Pyrrolizidine alkaloids (PAs) are feeding deterrents and toxic compounds to generalist herbivores. Among the PAs of Jacobaea vulgaris Gaertn, jacobine and erucifoline are the most effective against insect herbivores as indicated by correlative studies. Because little is known about the effect of jacobine and erucifoline as individual PAs, we isolated these compounds from their respective Jacobaea chemotypes. These PAs and other commercially available senecionine-like PAs, including senecionine, seneciphylline, retrorsine, and senkirkine, were tested as free base and N-oxide forms at a range of 0-70 ppm. Feeding bioassays using live insects are closer to the natural pattern but require relatively large amounts of test compounds. We, therefore, compared the toxicity of PAs using both Spodoptera exigua cell line and larval injection bioassays. Both bioassays led to similar results in the order of PA toxicity, indicating that the cell lines are a valuable tool for a first toxicity screen. Testing individual PAs, jacobine and erucifoline were the most toxic PAs, suggesting their major role in plant defense against generalist herbivores. Senkirkine and seneciphylline were less toxic than jacobine and erucifoline but more toxic than retrorsine. Senecionine was not toxic at the tested concentrations. For all toxic PAs, the free base form was more toxic than the N-oxide form. Our results demonstrate that structural variation of PAs influences their effectiveness in plant defense.

Plant Chemical Ecology Finally Gets to its Root(s)

Plants produce a wide array of secondary compounds that play critical roles in the interaction with their dynamic environment. Since the first issues of the Journal of Chemical Ecology in 1974, numerous papers have been published detailing the function of volatile and non-volatile plant compounds in interactions between plants, herbivores, and their natural enemies. Initially, plant chemical-ecological studies focused mainly on aboveground interactions. One can only speculate about what caused this focus; most likely because it is somuch easier to work on organisms and plant organs that one can see. However, roots have a ‘life of their own’ below the ground and may have as many, or even more, interactions with other organisms as the shoots. It has been known for centuries that plant roots contain high levels of medicinal compounds. A famous example is the roots of the legendary mandrake (Mandragora officinale), whose toxic and hallucinatory compounds have been used to concoct witchcraft potions as well as to kill opponents. Moreover, many well-studied defense compounds, such as pyrrolizidine alkaloids in common ragwort (Jacobaea vulgaris) and nicotine in (wild) tobacco, are exclusively produced in the roots before they are transported aboveground. For some reason, however, this was not interpreted as a sign that roots might need those chemicals as protection against herbivores and other enemies as well. Actually, roots generally were considered to be less prone to attack because they were assumed to be less apparent to herbivores.

Chemical variation in Jacobaea vulgaris is influenced by the interaction of season and vegetation successional stage

Knowledge on spatio-temporal dynamics of plant primary and secondary chemistry under natural conditions is important to assess how plant defence varies in real field conditions. Plant primary and secondary chemistry is known to vary with both season and vegetation successional stage, however, in few studies these two sources of variation have been examined in combination. Here we examine variations in primary and secondary chemistry of Jacobaea vulgaris (Asteraceae) throughout the growing season in early, mid, and late stages of secondary succession following land abandonment using a well-established chronosequence in The Netherlands.We investigated primary and secondary chemistry of both leaves and flowers, in order to determine if patterns during seasonal (phenological) development may differ among successional stages.The chemical concentration of primary and secondary chemistry compounds in J. vulgaris varied throughout the season and was affected by vegetation succession stage. Concentrations of pyrrolizidine alkaloid (PA) tertiary-amines were highest in flowers during early Summer and in fields that had been abandoned ten to twenty years ago. PA N-oxide concentrations of both leaves and flowers, on the other hand increased with the progression of both season and succession. In Spring and early Summer chlorophyll concentrations were highest, especially in the oldest fields of the chronosequence. During phenological development, nitrogen concentration increased in flowers and decreased in leaves revealing allocation of nutrients from vegetative to reproductive plant parts throughout the growing season.The highest concentrations of N-oxides and chlorophylls were detected in older fields. Thus, our results suggest that variations in plant patterns of nutritional and defence compounds throughout the growing season are depending on successional context.

Biochars produced from individual grassland species differ in their effect on plant growth

Biochar, pyrolyzed biomass, has been shown to be a promising way to improve plant productivity and soil quality. Biochar characteristics and its effect on plant performance depend strongly on the type of feedstock from which it is made. However, whether biochars produced from individual grassland species differ in their characteristics and effects on plant growth when applied to soil is poorly understood. The aim of this study was to examine how soil application of pyrolyzed and non-pyrolyzed biomass originating from different grassland species influences plant performance.We measured the growth of the forb Jacobaea vulgaris in soil amended with pyrolyzed or non-pyrolyzed biomass of seven different plant species, and in control soil without amendments.The characteristics (nutrient content, C:N) and effects on plant growth of both pyrolyzed and non-pyrolyzed biomass differed significantly between species from which the biomass originated (‘feedstock species’). For most feedstock species there was no relationship between the effects that the pyrolyzed and the non-pyrolyzed biomass had on plant performance. Our results show that pyrolyzed grassland species differ in their characteristics and their effect on plant growth when amended to soil. This shows that it is important to test what the effect of pyrolysing a chosen feedstock is on a species before applying it on a larger scale and that potentially biochar with predefined effects could be designed for specific purposes.

Local variation in conspecific plant density influences plant–soil feedback in a natural grassland

Several studies have argued that under field conditions plant–soil feedback may be related to the local density of a plant species, but plant–soil feedback is often studied by comparing conspecific and heterospecific soils or by using mixed soil samples collected from different locations and plant densities. We examined whether the growth of the early successional species Jacobaea vulgaris in soil collected from the field is related to the local variation in plant density of this species. In a grassland restoration site, we selected eight 8m×8m plots, four with high and four with low densities of J. vulgaris plants. In 16 subplots in each plot we recorded the density and size of J. vulgaris, and characteristics of the vegetation and the soil chemistry. Soil collected from each subplot was used in a greenhouse pot-experiment to study the growth of J. vulgaris, both in pure field soil and in sterile soil inoculated with a small part of field soil.In the field, flowering J. vulgaris plants were taller, the percentage of rosette plants was higher and seed density was larger in High- than in Low-density plots. In the pot experiment, J. vulgaris had a negative plant–soil feedback, but biomass was also lower in soil collected from High- than from Low-density plots, although only when growing in inoculated soil. Regression analyses showed that J. vulgaris biomass of plants growing in pure soil was related to soil nutrients, but also to J. vulgaris density in the field.We conclude that in the field there is local variation in the negative plant–soil feedback of J. vulgaris and that this variation can be explained by the local density of J. vulgaris, but also by other factors such as nutrient availability.

Preparative mass-spectrometry profiling of genotoxic pyrrolizidine alkaloids in Jacobaea vulgaris (syn. Senecio jacobaea) by spiral-coil countercurrent chromatography and ESI-MS/MS off-line continuous injection

Pyrrolizidine alkaloids (PAs) are genotoxic natural products. Almost 350 PAs are known with respective N-oxides. Legal regulations of PAs in food, and feed are discussed. There is a lack of available reference substances for targeted quantification [1]. PA-contamination was reported for honey, and bee products [2,3]. PA-contamination of retail ready-to-use lettuce was demonstrated. Morphological similarities of rocket salad (Diplotaxis tenuifolia, syn.: rucola), and the PA-plant Senecio vulgaris resulted in unintentional co-harvesting. In our study, PA-extract of J. vulgaris flower heads (Asteraceae) was fractionated by prep. spiral-coil countercurrent chromatography (spCCC, 5.7 L coil). The system n-hexane – EtOAc – MeOH – H2O (3:7:5:5) was used to separate 5 g of crude alkaloid extract. Obtained fractions were sequentially off-line injected to ESI-MS/MS. This target-guided isolation procedure [4] made use of selected ion traces of PAs. Elution of major (2, 5, 7), and minor (1, 3, 4, 6) PAs were monitored (altern. mode MS2, m/z 100 – 1500). The spCCC elution resulted in the fractionation of PAs, and one non-PA (8) in the extrusion-mode (8 not presented) [5]. Almost pure compounds were obtained for PAs 1, 2, 5, 7, and the non-PA 8 could be used as reference materials. Minor PAs were enriched and will be further purified with other separation techniques.

Changes in plant defense chemistry (pyrrolizidine alkaloids) revealed through high-resolution spectroscopy

Plant toxic biochemicals play an important role in defense against natural enemies and often are toxic to humans and livestock. Hyperspectral reflectance is an established method for primary chemical detection and could be further used to determine plant toxicity in the field. In order to make a first step for pyrrolizidine alkaloids detection (toxic defense compound against mammals and many insects) we studied how such spectral data can estimate plant defense chemistry under controlled conditions.In a greenhouse, we grew three related plant species that defend against generalist herbivores through pyrrolizidine alkaloids: Jacobaea vulgaris, Jacobaea erucifolia and Senecio inaequidens, and analyzed the relation between spectral measurements and chemical concentrations using multivariate statistics.Nutrient addition enhanced tertiary-amine pyrrolizidine alkaloids contents of J. vulgaris and J. erucifolia and decreased N-oxide contents in S. inaequidens and J. vulgaris. Pyrrolizidine alkaloids could be predicted with a moderate accuracy. Pyrrolizidine alkaloid forms tertiary-amines and epoxides were predicted with 63% and 56% of the variation explained, respectively. The most relevant spectral regions selected for prediction were associated with electron transitions and CH, OH, and NH bonds in the 1530 and 2100nm regions.Given the relatively low concentration in pyrrolizidine alkaloids concentration (in the order of mgg−1) and resultant predictions, it is promising that pyrrolizidine alkaloids interact with incident light. Further studies should be considered to determine if such a non-destructive method may predict changes in PA concentration in relation to plant natural enemies. Spectroscopy may be used to study plant defenses in intact plant tissues, and may provide managers of toxic plants, food industry and multitrophic-interaction researchers with faster and larger monitoring possibilities.

Intraspecific variation in plant size, secondary plant compounds, herbivory and parasitoid assemblages during secondary succession

During secondary succession on abandoned agricultural fields the diversity and abundance of insect communities often increases, whereas the performance and nutritional quality of early successional plants often declines. As the diversity and abundance of insects on a single plant are determined by characteristics of the environment as well as of the host plant, it is difficult to predict how insects associated with a single plant species will change during succession. We examined how plant characteristics of the early successional plant species ragwort (Jacobaea vulgaris), and the herbivores and parasitoids associated with these plants change during secondary succession. In ten grasslands that differed in time since abandonment (3–26 years), we measured the size and primary and secondary chemistry of individual ragwort plants. For each plant we also recorded the presence of herbivores in flowers, leaves and stems, and reared parasitoids from these plant parts. Ragwort plants were significantly larger but had lower nitrogen concentrations in recently abandoned sites than in older sites. Pyrrolizidine alkaloid (PA) composition varied among plants within sites but also differed significantly among sites. However, there was no relationship between the age of a site and PA composition. Even though plant size decreased with time since abandonment, the abundance of stem-boring insects and parasitoids emerging from stems significantly increased with site age. The proportion of plants with flower and leaf herbivory and the number of parasitoids emerging from flowers and leaves was not related to site age. Parasitoid diversity significantly increased with site age. The results of our study show that ragwort and insect characteristics both change during secondary succession, but that insect herbivore and parasitoid abundances are not directly related to plant size or nutritional quality.

Hyperspectral reflectance of leaves and flowers of an outbreak species discriminates season and successional stage of vegetation

Spectral reflectance can be used to assess large-scale performances of plants in the field based on plant nutrient balance as well as composition of defence compounds. However, plant chemical composition is known to vary with season – due to its phenology – and it may even depend on the succession stage of its habitat. Here we investigate (i) how spectral reflectance could be used to discriminate successional and phenological stages of Jacobaea vulgaris in both leaf and flower organs and (ii) if chemical content estimation by reflectance is flower or leaf dependent.We used J. vulgaris, which is a natural outbreak plant species on abandoned arable fields in north-western Europe and studied this species in a chronosequence representing successional development during time since abandonment. The chemical content and reflectance between 400 and 2500nm wavelengths of flowers and leaves were measured throughout the season in fields of different successional ages. The data were analyzed with multivariate statistics for temporal discrimination and estimation of chemical contents in both leaf and flower organs.Two main effects were revealed by spectral reflectance measurements: (i) both flower and leaf spectra show successional and seasonal changes, but the pattern is complex and organ specific (ii) flower head pyrrolizidine alkaloids, which are involved in plant defence against herbivores, can be detected through hyperspectral reflectance.We conclude that spectral reflectance of both leaves and flowers can provide information on plant performance during season and successional stages. As a result, remote sensing studies of plant performance in complex field situations will benefit from considering hyperspectral reflectance of different plant organs. This approach may enable more detailed studies on the link between spectral information and plant defence dynamics both aboveground and belowground.

Pyrrolizidine Alkaloid Composition Influences Cinnabar Moth Oviposition Preferences in Jacobaea Hybrids

Plants produce a variety of secondary metabolites (PSMs) that may be selective against herbivores. Yet, specialist herbivores may use PSMs as cues for host recognition, oviposition, and feeding stimulation, or for their own defense against parasites and predators. This summarizes a dual role of PSMs: deter generalists but attract specialists. It is not clear yet whether specialist herbivores are a selective force in the evolution of PSM diversity. A prerequisite for such a selective force would be that the preference and/or performance of specialists is influenced by PSMs. To investigate these questions, we conducted an oviposition experiment with cinnabar moths (Tyria jacobaeae) and plants from an artificial hybrid family of Jacobaea vulgaris and Jacobaea aquatica. The cinnabar moth is a specialist herbivore of J. vulgaris and is adapted to pyrrolizidine alkaloids (PAs), defensive PSMs of these plants. The number of eggs and egg batches oviposited by the moths were dependent on plant genotype and positively correlated to concentrations of tertiary amines of jacobine-like PAs and some otosenine-like PAs. The other PAs did not correlate with oviposition preference. Results suggest that host plant PAs influence cinnabar moth oviposition preference, and that this insect is a potential selective factor against a high concentration of some individual PAs, especially those that are also involved in resistance against generalist herbivores.