Fig. 1: Investigation of chemical ecological inter-actions between different organisms
Fig. 3: Functions of the symbiosis
Fig. 4: Arabidopsis halleri
Fig. 5: Bunias orientalis
Fig. 6: Erodium cicutarium
Fig. 7: Influences of the chemistry by Tanacetum vulgare on aphids and vice versa
Fig. 8: Investigation of pollination and florivory in different tansy chemotypes
Fig. 9: Laser microscope
Fig. 10: Aphids on artificial diet
Fig. 11: Sitobion avenae
Fig. 12: Wheat heads infested with S. avenae
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-Q-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).
Within the Collaborative Research Centre 212 we study, how individuals of the sawfly Athalia rosae conform to the ecological and social niche and whether this is adaptive. Therefore, animals are kept for two generations in constant or changing environmental conditions and influences on life history traits, physiology, immunity and chemical phenotypes of the individuals are measured.
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 (Fig. 2).
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. 3). 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. 4) 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.
The spotted wing drosophila, Drosophila suzukii, is endemic to Asia but has been reported in Europe first from Spain in 2008. Since then it has become well established as an invasive pest in large parts of the European continent. In 2011 this species was found in Germany for the first time and causes sometimes severe economical damage in fruit crops and vineyards since then. As part of an EU-funded Interreg-project (Invaprotect: PI: Dr. Michael Breuer, Staatliches Weinbauinstitut Freiburg) the potential risks emanating from this pest insect for viticulture are examined by studying the habitat-dependent activity of D. suzukii in field trials. Furthermore, preferences of D. suzukii for different grape varieties are tested in laboratory assays and possible factors that influence the behaviour are analysed. Collaboration with Dr. Michael Breuer, Staatliches Weinbauinstitut Freiburg
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 try to explain the underlying mechanisms for such successful establishment. Among others it is thought that invasive populations possibly change their chemical profiles due to a change in the herbivore pressure, which may go along with an allocation of resources to more competitive growth. For example, the Brassicaceae Bunias orientalis (Fig. 5) originates from the Caucasus, but spreads within the Eurasian continent further to the West. We investigate the chemical and morphological variability of populations of different origin and study effects of these individual differences on interactions with herbivorous insects and pathogens in the field.
Allelopathy may enable non-dominant plants to invade new areas and successfully outcompete their new neighboring plants. Redstem filaree (Erodium cicutarium, Geraniaceae, Fig. 6) 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. We investigate whether and how root and stem derived specialised 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. 7). For example, specialised aphids prefer certain chemotypes. In turn, the phloem sap composition and leaf senescence can depend on aphid attack. We investigate whether the phloem sap composition differs between chemotypes (depending on the aphid species) and whether different aphid species trigger different signaling pathways and thus affect metabolite patterns 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 are investigated (Fig. 8).
Various primary and specialised 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 impacts 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, for example using the aphid stylectomy technique and chemically analysed (Fig. 9). 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 wheat in dependence of the presence of mykorrhiza and further effects on the performance and preferences of aphids (Fig. 11/12). Furthermore, we study drought effects on wheat primary and specialised leaf, fruit and phloem sap metabolites and relate these to potential effects on herbivores.
The high susceptibility to pests and diseases in the cultivation of cultivated strawberries requires the use of a great variety of pesticides. Along with their degradation products, these pesticides can accumulate in the environment and damage various organisms. Some of these active substances can also produce measurable changes in the plant metabolism of treated plants and could thus also affect the composition of the flower scents as well as the aroma and taste-relevant metabolites of the fruits. The aim of this project is to investigate the influence of fungicides on plant and fruit metabolites which are applied before or during the flowering period and also whether these fungicides influence the flower scents and the nectar microbiome. The project will further investigate if the findings obtained in the laboratory can be transferred to the natural pollinator community in the field.
Insect natural enemies such as predators and parasitoids play an important role in biological pest control and their foraging efficiency may determine if herbivore-infestations in agricultural fields reach the threshold above which insecticides are applied. Most natural enemy species use herbivore-induced plant volatiles (HIPVs) to detect herbivore-infested plants from a distance, but we only have a limited understanding on the way information is encoded in HIPV blends, how different species of natural enemies use this information and how changes in abiotic conditions influence the reliability and detectability of the volatile signals under field conditions. In this project, we study the responses of several natural enemy species towards different HIPV-blends (e.g., blends induced by chewing or sucking herbivores) under laboratory and field conditions in order to understand how the enormous diversity of HIPV blends influences the foraging efficiency of these beneficial insects.