Plant roots are colonized by a great variety of fungi, for instance, the highly investigated mycorrhizal fungi and the elusive (dark) septate endophytes (DSE). The mycorrhizal symbiosis was multiple times reported as beneficial for the plant as well as the mycorrhizal fungi with both being involved in a vivid bi-directional nutrient transfer, while very little is known about the function of DSE. However, these fungi have been reported for over 140 plant families and manage to colonize plant families generally considered as ‘non-mycorrhizal’ (e.g. Caryophyllaceae, Cyperaceae).
Material and Methods
Selected Caryophyllaceae and neighbouring ‘non-mycorrhizal’ as well as mycorrhizal plants as reference species were sampled in NE-Bavaria. Fungal association was checked by staining approaches. The abundance of the stable isotopes 13C and 15N was measured (EA-IRMS) and data were normalized to enrichment factors which disclose the relative difference between the target (DSE-dominated) and reference plants.
DSE-colonization was significantly higher in plants of the Caryophyllaceae. Caryophyllaceae were significantly enriched in the stable isotopes 13C and 15N compared to reference plants. Nitrogen concentration was significantly higher in mycorrhizal reference plant species, characterized by low DSE-colonization.
DSE are known to be capable of utilizing organic detrital nutrients and thus, may transfer those to ‘non-mycorrhizal’ plants. We conclude that DSE could provide a distinct nitrogen-nutrient source for the plant, thereby changing its 15N pattern which consequently differs from mycorrhizal plant species’ 15N abundance. This study not only provides further support for suggestions that plants’ 15N abundance is largely influenced by their fungal partner but also adds one puzzle stone to the function of the elusive DSE.