Fig. 4: Functions of the symbiosis
Fig. 6: bunias orientalis
The qualitative and quantitative composition of all metabolites of a plant (metabolome) depends on endogenous factors as well as environmental factors such as nutrients and disturbances. Changes in the metabolite profiles have direct effects on organisms that feed on the plant. We investigate both the variation of metabolite profiles with high temporal and local resolution (with LC-TOF-MS and GC-MS) and the influences of such changes on herbivorous organisms in standardised laboratory systems as well as in the field (Fig. 1).
Insects have to adapt to novel anthropogenically-induced environmental changes. The expansion of urbanisation and of agriculturally-used land areas causes an increase in insecticide usage and a decrease of natural habitats and population sizes, which raises the risk of inbreeding. In previous studies, we showed that factors such as food quality and rearing density have significant impacts on the growth and behaviour of larvae and adults of the mustard leaf beetle, Phaedon cochleariae (Fig. 2). In this project we investigate the effects of sublethal concentrations of insecticides and of inbreeding on performance parameters and behavioural phenotypes as well as on physiochemical characteristics of the leaf beetle.
Herbivorous insects have evolved various strategies to deal with the defences of their host plants. The plant family of Brassicaceae is well known for its glucosinolate-myrosinase defence system, in which toxic hydrolysis products such as isothiocyanates are formed once the substrate comes into contact with the myrosinase enzymes. Thus, insects feeding on Brassicaceae must metabolise the glucosinolates in a way that they avoid the formation of toxic breakdown products. A fascinating diversity of insect counteradaptations to the plant defence system has been revealed within the Lepidoptera, and in species of Hemiptera, Hymenoptera and one Coleoptera. Using various chemical-analytical methods, we investigate the detoxification mechanisms of larvae and adults of two leaf beetle species, whose strategies are unknown so far.
Arbuscular mycorrhiza (AM) is a widely-distributed symbiosis between terrestrial plants and AM-fungi (Fig. 3). Thereby, the plant supplies the fungus with photoassimilates, whereas in return the fungus improves the plant provision with minerals and water. Due to the very close association between both symbionts and the high carbon sink of the AM fungus, the symbiosis not only influences the metabolite profile of the roots but also the resource allocation in aboveground tissues. We investigate AM-induced metabolic changes in different plant parts of colonized plants using chromatographic and spectroscopic analyses. Studies are carried out with model systems that allow us to disentangle general and species-specific responses of the plant hosts to colonising AM-fungi. Moreover we are interested whether the plant chemistry affects the behavior and performance of herbivorous insects.
Rhizobia are soil bacteria, which symbiotically interact with plants of the Fabaceae. The bacteria colonise the plant roots by forming so-called nodules, fix atmospheric nitrogen and deliver nitrogen-containing compounds to their hosts, being provided with carbon-based metabolites in return (Fig. 4). The additional nitrogen input can not only enhance the crop yield, but probably also influences plant chemistry. In this project, we investigate the influences of the interaction with rhizobia on plant morphology and biochemistry of different agricultural and model plant species. Therefore, effects on the leaf and on the phloem sap metabolome are examined. Because a modification of plant chemistry probably also affects plant antagonists, plant-mediated effects on the performance of herbivores with different feeding modes are explored as well.
The species Arabidopsis halleri (Brassicaceae, Fig. 5) occurs at sites contaminated by heavy metals and can hyperaccumulate high levels of heavy metals like cadmium and zinc in its above-ground biomass. We investigate the ecological role of metal accumulation in the context of interactions between these plants and phloem-feeding herbivores, such as Myzus persicae. Moreover, we are interested in potential trade-offs between organic and elemental defences in hyperaccumulating plants. In this DFG-funded project we cooperate with the Universities of Bochum and Bayreuth.
Plant species that were introduced to new habitats in which they were not native before can generate severe problems to the environment. They can be very successful competitors and thereby displace the native flora. Several hypotheses exist trying to explain the underlying mechanisms for such successful establishment. Among others it is thought that invasive populations possibly change their chemical profile due to a change in the herbivore pressure which may go along with an allocation of resources to more competitive growth. For example, common tansy (Tanacetum vulgare, Asteraceae, Fig. 6) is of Eurasian origin but is invasive in Northern America. The plant is characterised by the presence of essential oils, whose composition can vary dramatically between individuals. We investigate the chemical and morphological variability of populations of different origin of selected plant species and effects of this individual differences on interactions in the field.
Allelopathy may allow non-dominant plants to invade new areas and successfully outcompete their new neighboring plants. Redstem filaree (Erodium cicutarium, Geraniaceae, Fig. 7) is a serious weed in field cropping systems and therefore a well-studied plant in terms of ecological traits that may be causal to its invasiveness in North America. It shows a high ability to morphologically adapt to environmental conditions. However, chemical plasticity and particularly allelopathic effects remain largely unexplored to date. We investigate whether and how root and stem derived secondary metabolites influence the survival and biomass production of neighboring crop plants.
Common tansy, Tanacetum vulgare, shows distinct terpene profiles in its leaves, forming so-called chemotypes. This high chemical diversity influences interactions with herbivores (Fig. 8). For example, specialised aphids prefer certain chemotypes. In turn, the phloem composition and leaf senescence can depend on the aphid attack. We investigate whether the phloem composition differs between chemotypes (depending on the aphid species) and whether different aphid species trigger different signaling pathways and thus affect metabolite pattern to different degrees.
Pollinator-dependent, pollen-rich plants may face a trade-off between the repellence of pollen-feeders and attraction of pollen-dispersers. Common tansy (Tanacetum vulgare, Asteraceae) forms chemotypes with characteristic patters of terpenes in leaves and flowers, which are differentially frequented by herbivores. In this project the relationship of chemotypes and pollination as well as changes in terpene composition after successful pollination or presence of florivores is investigated (Fig. 9).
Various primary and secondary metabolites are transported via the phloem sap in the plant sieve tubes. The chemical composition of the phloem sap can be influenced both by abiotic and biotic environmental factors In several projects, we investigate the impact of various environmental factors (e. g., fertilisation, drought, competition, symbioses) on the phloem sap chemistry of different plant species. Therefore, pure phloem sap is collected using the aphid stylectomy technique and chemically analysed (Fig. 10). To understand how phloem-feeding herbivores (e. g., aphids) are influenced by chemical modifications of the phloem sap, we study the performance of aphids on artificial diets varying in chemical composition (Fig. 11). Moreover, chemical analyses of aphid honeydew allow insights into the dietary metabolism within the aphids. The overall aims of these studies are to characterise the factors, which are relevant for aphid nutrition, and to understand aphid development on plants in nature.
The impact of climate change on agricultural plants is becoming increasingly important. In particular, rising temperatures, CO2 levels and more intensive drought stress periods are of concern in this context. In this project, we investigate the impacts of continuous versus pulsed drought stress on the performance and preferences of insect herbivores like the grain aphid (Sitobion avenae) on wheat (Fig. 12/13). Moreover, we study drought effects on wheat primary and secondary leaf, fruit and phloem exudate metabolites and relate these to potential effects on herbivores.
Inbreeding depression refers to the reduction of fitness in offspring produced by non-random mating. The deleterious effects of inbreeding unfold in manifold phenotypic traits that can be directly related to fitness (e.g., numbers of flowers produced by a plant), but also in traits related to resistance against environmental stressors such as herbivores. In this project, we study the interactive effects of inbreeding and herbivory on European native and North American invasive populations of Silene latifolia (White Campion, Fig. 14). We examine i) the effects of inbreeding on the composition of secondary metabolites potentially involved in responses to herbivory, ii) whether such metabolic changes modify the plant resistance against herbivores and iii) whether herbivore attack influences the expression of inbreeding depression in traits directly related to plant fitness. Moreover, we explore how differences in the strength of herbivore attack between native and invaded habitats interact with the effects of inbreeding depression over evolutionary time scales.