Root Allelochemical Interactions of t. Umbellifer Peucedanum

The aim of this project is to investigate the effects of plant allelochemicals (= secondary plant metabolites) on microfungi present in the host plant rhizosphere. Allelochemicals are plant metabolites which are not relevant for life-sustaining processes, such as photosynthesis and respiration. Regarding the survival of the plant individual in the ecosystem, an important role, however, is attributed to them. These substances, e.g. flavonoids, coumarins, alkaloids, or terpenoids, are considered to be chemical defense agents against microorganisms and herbivorous insects. The allelochemical composition in the subterranean root system of the umbelliferous genus Peucedanum is known and has been the object of previous studies. Consequently, four species have been chosen to be included in this project on basis of diverse allelochemical profiles. P. austriacum only grows in forest clearings in the Wiener Wald and P. oreoselinum can only be found on more acidic soils in the Hundsheimer Berge; P. alsaticum and P. cervaria occur in dry grassland in both localities. Microfungi represent the greatest species richness among soil microorganisms. Contrary to the biodiversity of higher plants or insects, fewer attention has been paid to it. Fundamental research aims comprise the characterization of the predominant microfungi in the root microhabitat of each selected Peucedanum species in contrast to the surrounding soil, and the comparison of the microfungal communities on plant species- and population level. Molecular methods are applied for identification besides of classical morphological methods. Representative isolates are to be kryoconserved in the culture collection VIAM (Vienna Institute of Applied Microbiology) for documentation and further use. To determine the influence of different plant allelochemicals on the germination and growth of selected microfungi, a series bioassays are to be carried out. The obtained data are to clarify the extent of plant allelochemical influence on the microfungal community in this study model.

Rhizosphere denotes that soil volume influenced by the plant root. Sloughed off cells, mucilage and root exsudates represent an essential carbon source for many soil microorganisms. Consequently, regarding studies of plant- microbe interactions, this region represents a scenario of high interest. During the last years, some studies have pointed to the fact that a plant species might influence the species composition of its rhizosphere microbial community. Thus, we focused low-molecular root compounds that might constitute potential signals in this context, such as sugars, amino acids, and secondary metabolites. Filamentous microfungi represent, besides bacteria, major components of soil microbial communities. Many of them can also be maintained as laboratory cultures that are essential to carry out the necessary bioassays. For those, we chose 30 representative isolates to study growth and development when grown on differently-composed substrates. These comprised extract fractions of different solubility (water-soluble and non-water-soluble), derived from the roots of two model plants, the umbellifers Peucedanum alsaticum and P. cervaria. Both plants are typical elements of dry grassland communities in Central and Eastern Europe. Their soils are undisturbed and contain a biodiversity of microorganisms, contrary to cultured soils that have become impoverished by one-sided culture measurements. Our results especially suggest sugars to constitute discriminating signals in this context. Mixtures, such as they occur in plant roots, however, affected soil fungi more specifically than single compounds in comparable concentrations. Both investigated umbellifers accumulated prominent amounts of the sugar alcohol mannitol in their roots, contrary of other plants growing nearby. Fungi, which spent there whole life cycle within plant tissues, but do not cause any disease symptoms, are denoted endophytes. Especially such fungi showed slowed growth, a possible adaptation, when grown on extracts derived from their immediate host plants, the umbellifers. Extracts from roots of other plant species did not affect the identical fungal isolates similarly. Besides sugars, allelochemicals can also influence the composition of fungal communities in the rhizosphere. Despite the similarity in their sugar composition, the roots of the two umbellifers contain quite diverse allelochemicals. Results from our investigations suggest that variable susceptibility of single fungal species towards these chemicals may also represent an important criterion to establish itself within a specific plant root microbial community. Besides new insights into the ecology of plant-fungus interactions, this research may constitute a basis to develop new culture techniques for crop plants, especially in concern of the fact that, nowadays, increased yields cannot be achieved by extension of cultivation areas alone.