Hungry for fungi? – Quantification of organic C and N flows into mycoheterotrophic plants on a stand level
P 1.10 in Funktion von Ökosystemen
A number of plants from different families, e.g. Orchidaceae and Ericaceae, are known to live in a partial or full feeding dependence upon their ectomycorrhizal fungal association and therefore are called partial or full mycoheterotrophs. By reason of the heterotrophic nutrition these plants are of an isotope composition similar to the fungal substrate and are therefore enriched in 13C and 15N compared to reference plants. Based on these characteristic isotope signatures in plant tissues, the percental contribution of organic C and N derived from fungi to the total C and N of mycoheterotrophic plants was already estimated in former studies. However, the quantitative fungi-derived C and N gain on stand level was not investigated up to now. Hence this study addresses the calculation of the annual mass of C and N derived from fungi of all mycoheterotrophic plants within one hectare beech forest. In order to quantify this mass the biometric data from representatives of four partially (Cephalanthera damasonium, Cephalanthera rubra, Epipactis atrorubens and Orthilia secunda) and two fully mycoheterotrophic plant species (Neottia nidus-avis and Monotropa hypopitys) were brought together with isotope data of these plants for the first time. Mapping of all mycoheterotrophic plants grown on the study side allowed the expansion of the quantification attempt to the stand level. Summing up, the results revealed an above ground dry weight for 2488 target plants of 346 g · ha-1 · a-1 containing 103 g organic C (30 %) and 6 g organic N (2 %) from the fungal association. Compared to the annual NPP of the forest area the C and N flow into the mycoheterotrophic plants is marginal but vital for the individual plant itself.