Exploiting mycorrhizas in broad daylight: Partial mycoheterotrophy is a common nutritional strategy in meadow orchids

Abstract

4.Synthesis. Our findings demonstrate that partial mycoheterotrophy is a trophic continuum between the extreme endpoints of autotrophy and full mycoheterotrophy, Paper previously published as Standard Paper

Stable isotope signatures of underground seedlings reveal the organic matter gained by adult orchids from mycorrhizal fungi

“…Baylis () argued that the morphology of the orchids’ root systems with few, generally fleshy and unbranched roots has all the characteristics of plants with a high dependency on mycorrhizal fungi to gain mineral nutrients (Peterson, Massicotte, & Melville, ). Furthermore, there is also supporting evidence from stable isotope natural abundance analyses and measurements of nitrogen concentrations that chlorophyllous orchid species associated with rhizoctonia fungi are partially mycoheterotrophic (Gebauer et al., ; Girlanda et al., ; Schiebold et al., ). Most orchid species inhabiting sunny meadows lack 13 C enrichment or are even significantly depleted in 13 C relative to autotrophic references.…”

Mycorrhizal symbioses and the evolution of trophic modes in plants

“…Similarly, normalized enrichment factors for 13 C continuously increased from zero to five (Figure ). In another study, Schiebold, Bidartondo, Lenhard, Makiola, and Gebauer () investigated stable isotope signatures in a range of meadow orchids associating with rhizoctonia fungi and found significant enrichment in 15 N and 2 H, although no signs of 13 C enrichment were found and in some cases even 13 C depletion. Stöckel, Těšitelová, Jersáková, Bidartondo, and Gebauer () compared enrichment factors between protocorms and adult plants of both orchids associated with ectomycorrhizal fungi and rhizoctonia.…”

“…Due to its cryptic manifestation, partial mycoheterotrophy has so far only been confirmed for over 20 species of Orchidaceae (Hynson et al, ; Schiebold et al, ), although it seems much more likely that many more orchid species, if not all, show evidence of partial mycoheterotrophy (Schiebold et al, ). Further evidence for partial mycoheterotrophy has been found in c. 8 species of Ericaceae (within Pyrola, Orthilia and possibly Chimaphila and Moneses ), a single species of Burmanniaceae ( Burmannia coelestis ), and has been suggested for Gentianaceae ( Bartonia virginica and Obolaria virginica ) (Cameron & Bolin, ; but see Hynson, Madsen, et al, ; Hynson, Weiss, et al, ).…”

“…The latter have long been assumed to be autotrophic as adults, whereas the former usually show partial or full mycoheterotrophy. However, the assumed autotrophy of rhizoctonia‐associated orchid species has recently been challenged (Gebauer et al, ; Schiebold et al, ; Schweiger et al, ). Moreover, detailed molecular analyses using high‐throughput sequencing techniques have shown that many so‐called ‘rhizoctonia‐associated’ species also associate with ectomycorrhizal fungi and vice versa (Jacquemyn et al, ; Jacquemyn, Brys, Waud, Busschaert, & Lievens, ; Jacquemyn, Waud, et al, ), indicating that a strict distinction between rhizoctonia‐associated and ectomycorrhiza‐associated species cannot be maintained, neither based on their stable isotope signatures nor their mycorrhizal communities.…”

Mixotrophic orchids do not use photosynthates for perennial underground organs

“…These plants with two carbon sources are termed mixotrophic, and pave the evolutionary way to full mycoheterotrophy (Selosse & Roy, ). Mixotrophy enables them to adapt to shaded conditions (Julou et al ., ; Preiss et al ., ; with some exceptions: Girlanda et al ., ; Schiebold et al ., ) and sometimes drives a reduction of their photosynthetic abilities (Girlanda et al ., ). Their study is therefore of crucial interest to an understanding of the evolution to full mycoheterotrophy.…”