Data from: Exploiting mycorrhizas in broad daylight: partial mycoheterotrophy is a common nutritional strategy in meadow orchids.

Partial mycoheterotrophy (PMH) is a nutritional mode in which plants
utilize organic matter, i.e. carbon, both from photosynthesis and a fungal
source. The latter reverses the direction of plant-to-fungus carbon flow
as usually assumed in mycorrhizal mutualisms. Based on significant
enrichment in the heavy isotope 13C, a growing number of PMH orchid
species have been identified. These PMH orchids are mostly associated with
fungi simultaneously forming ectomycorrhizas with forest trees. In
contrast, the much more common orchids that associate with rhizoctonia
fungi, which are decomposers, have stable isotope profiles most often
characterized by high 15N enrichment and high nitrogen concentrations but
either an insignificant 13C enrichment or depletion relative to
autotrophic plants. Using hydrogen stable isotope abundances recent
investigations showed PMH in rhizoctonia-associated orchids growing under
light-limited conditions. Hydrogen isotope abundances can be used as
substitute for carbon isotope abundances in cases where autotrophic and
heterotrophic carbon sources are insufficiently distinctive to indicate
PMH. To determine whether rhizoctonia-associated orchids growing in
habitats with high irradiance feature PMH as a nutritional mode, we
sampled 13 orchid species growing in montane meadows, four forest orchid
species and 34 autotrophic reference species. We analysed δ2H, δ13C, δ15N
and δ18O and determined nitrogen concentrations. Orchid mycorrhizal fungi
were identified by DNA sequencing. As expected, we found high enrichments
in 2H, 13C, 15N and nitrogen concentrations in the
ectomycorrhiza-associated forest orchids, and the rhizoctonia-associated
Neottia cordata from a forest site was identified as PMH. Most orchids
inhabiting sunny meadows lacked 13C enrichment or were even significantly
depleted in 13C relative to autotrophic references. However, we infer PMH
for the majority of these meadow orchids due to both significant 2H and
15N enrichment and high nitrogen concentrations. Pseudorchis albida was
the sole autotrophic orchid in this study as it exhibited neither
enrichment in any isotope nor a distinctive leaf nitrogen concentration.
Synthesis. Our findings demonstrate that partial mycoheterotrophy is a
trophic continuum between the extreme endpoints of autotrophy and full
mycoheterotrophy, ranging from marginal to pronounced. In
rhizoctonia-associated orchids, partial mycoheterotrophy plays a far
greater role than previously assumed, even in full light conditions.