Networks instead of self-reliance: meadow orchids surprise researchers in Bayreuth
University of Bayreuth, Presse Release No. 092/2017, 21 July 2017
Meadow orchids, which are capable of producing adequate nourishment for themselves in full sunlight via photosynthesis, often additionally enter into a symbiosis with fungi to meet their nutrient requirements. They only create a fraction of the needed carbon themselves, drawing the rest from fungi with which their roots form underground networks. This was discovered by scientists at the University of Bayreuth together with research partners in Great Britain. They have published their unexpected findings in the Journal of Ecology.
Students of the University of Bayreuth collect samples of field orchids in a mountain valley in Vorarlberg. Photo: Gerhard Gebauer.
The team of researchers led by Prof. Dr. Gerhard Gebauer at the University of Bayreuth just discovered a few years ago that green orchids living on the forest floor with very limited light conditions “tap into” neighbouring fungi with their roots. This allows them to add to the carbon reserve they built up themselves via photosynthesis and completely satisfy their needs. In this connection, a three-way relationship often results, since some of the types of fungi “tapped into” by the orchids are already in a symbiotic relationship with the forest trees. The scientists can explain such underground supply networks by analyzing the frequency at which carbon and nitrogen isotopes occur in neighbouring orchids, fungi, trees, and other plants. Isotopes are atoms of the same element which are only distinguished by the number of neutrons in their core. The Laboratory for Isotope Biogeochemistry at the Bayreuth Centre of Ecology & Environmental Research (BayCEER) has all the equipment necessary to measure isotope frequency from organisms.
For the first time ever, the experiments were now applied extensively to orchids that grow in open meadows and do not have any limitations with regard to sunlight. It became clear that orchids do not only turn to fungi for additional nourishment when there is too little sunlight. This so-called “myco-heterotrophy” occurs in orchids that would otherwise be able to nourish themselves in principle. In particular, the scientists compared four orchid species that grow on the forest floor and get part of their carbon supply from fungi along with 13 orchid species that grow in sunny mountain pastures in the Alps. The latter differ from the forest orchids in that they have a significantly lower level of carbon isotope 13C. However, levels of the hydrogen and nitrogen isotopes 2H and 15N along with nitrogen concentrations are significantly higher in the field orchids. “These findings came as a surprise. Taken together with isotope analyses carried out on other plants, we were able to conclude that the orchids supplied with adequate sunlight still prefer a symbiotic relationship with fungi to nourishing themselves independently,” explained Prof. Gebauer, Director of the Laboratory for Isotope Biogeochemistry.
What makes the orchids avoid exhausting their own photosynthetic potential? “We believe that the carbon supplied by the fungi creates competitive advantages for the meadow orchids. With the help of the fungi, they can also survive unfavourable climate conditions over the course of many years below the ground surface,” said biologist Julienne Schiebold (M.Sc.), lead author of the article.
Laboratory work on a mass spectrometer to determine isotope frequency. Left: Julienne Schiebold, right: Prof. Dr. Gerhard Gebauer. Photo: Christian Wißler
With funding from the German Research Foundation (DFG), the scientists in Bayreuth carried out their experiments together with scholars from Imperial College in London and the Royal Botanic Gardens, Kew. Students enrolled in the master’s programmes Biodiversity & Ecology and Molecular Ecology at the University of Bayreuth also participated – not just in the laboratory experiments, but also in excursions to Vorarlberg. The findings from several students’ final theses were used in the article published in the Journal of Ecology.
“The University of Bayreuth’s degree programmes in biology and environmental science are designed to give students plenty of opportunities to contribute their own ideas and concepts to demanding research projects,” said Prof. Gebauer, who has been addressing nutrient networks of plants and fungi for many years.
Julienne M.-I. Schiebold, Martin I. Bidartondo, Florian Lenhard, Andreas Makiola und Gerhard Gebauer,
Exploiting mycorrhizas in broad daylight: Partial mycoheterotrophy is a common nutritional strategy in meadow orchids,
Journal of Ecology (2017), DOI: 10.1111/1365-2745.12831.
Prof. Dr. Gerhard Gebauer
Laboratory of Isotope Biogeochemistry(BayCEER)
University of Bayreuth
Phone: +49 (0) 921 / 55-2060
University of Bayreuth
Universitätsstr. 30 / ZUV
Phone: +49 (0)921 / 55-5356