Stable isotope analyses featuring carbon isotopes (13C) could show the usage of two different carbon sources, autotrophy and heterotrophy, for C3-hemiparasites on C4- or CAM-hosts . Nevertheless, this 13C approach failed for the more frequently occurring C3-C3 parasite-host-pairs. To overcome this obstacle, we used stable hydrogen isotopes (2H) as substitute for 13C  within a C3-Orobanchaceae-sequence (root parasites) graded by morphological features .
Material and Methods
Parasitic Orobanchaceae and Sanatalaceae (9 species, 67 individuals) and fully autotrophic potential host plants (25 species, 199 individuals) were collected in Germany and Austria in 2016. Development-changes of Rhinanthus minor (5) and Viscum album (3) were analysed in a time series. A multielement stable isotope natural abundances approach (EA-IRMS: δ13C, δ15N; TC-IRMS: δ2H, δ18O) was realized.
Hydrogen values are counterbalanced by transpiration (2H depletion) and gain of host-derived organic matter (2H-enriched). The influence of the transpiration is subtracted out of the δ2H values through the δ18O values, which are exclusively driven by a higher transpiration of the parasite compared to the host. Different efficiencies of nutrient translocation were estimated within the Orobanchaceae-sequence.
Time series revealed development-dependent shifts (young: heterotrophic, adult: autotrophic) for Rhinanthus minor and Viscum album (plus initial self-heterotrophy).
Due to higher transpiration and lower water-use efficiency a depletion in δ2H, δ13C and δ18O should be expected for tissues of hemiparasites. Stepwise enrichment in 2H stable isotope is caused by heterotrophic stages and can at least be calculated semi-quantitatively.
Time series approaches to evaluate development-dependent isotopic abundances are recommended for further parasitic species.
High resolution picture of poster 6.7