Uni-Bayreuth grafik-uni-bayreuth



Carbon and nitrogen gains of selected orchids from Western Australia

Johanna Pausch1, Mark Brundrett2, Martin I. Bidartondo3, Gerhard Gebauer1
1 BayCEER - Laboratory of Isotope Biogeochemistry, University of Bayreuth, Germany
2 School of Plant Biology, The University of Western Australia, Perth, Australia
3 Imperial College and Royal Botanic Gardens, Kew, UK

P 1.8 in Ecosystem Function

Within the high diverse orchid family associations with mycorrhizal fungi play an important role. The orchid depends on the fungus already in the earliest stage of its development when the fungus supports the germination of the minute orchid seeds. The fungi can serve as a nitrogen (N) and carbon (C) source also in the adult stage. While achlorophyllous (myco-heterotrophic) orchids are completely dependent on the fungus for their whole life time, some green orchids, capable of photosynthesis, can also partially obtain their C and N from the fungus (partial myco-heterotrophy) during adulthood. In this study the nutritional mode of seven different orchid genera of Western Australia was investigated with two different approaches: To detect the C and N transfer from the fungus to the orchid we used natural stable isotope abundance measurements. To provide insight into the photosynthetic ability of the orchid, on the other hand, a 13CO2 pulse labelling approach was chosen. Supporting data for both approaches were achieved from chlorophyll content measurements, determination of the fungi associated with each orchid, and measurements of the relative light availability at the sampling locations.The most conclusive results were obtained by the natural stable abundance measurements. In contrast to former investigations from Central and Mediterranean Europe and from North America where δ15N and δ13C values of autotrophic reference plants clustered in narrow ranges, our results show large variations between the references. Due to these large variations within the group of reference plants it is difficult to clearly identify the nutritional mode of the orchids. Nevertheless, the findings give evidence that there is a tendency of partial myco-heterotrophy for two out of the seven genera. 

last modified 2009-03-08