Photosynthesis sets plants apart from other organisms and is the key to primary productivity on earth. However, not all plants are photoautotrophic. Mycoheterotrophic (MH) plants turned the tables covering their carbon demand at least partially or timewise through heterotrophy. In the case of MH plants fungi serve as an exclusive or additional carbon source.
While Orchidaceae and Ericaceae are currently the most intensively investigated families with mycoheterotrophic representatives, unfortunately, a lack of investigations on partial mycoheterotrophy exists for the most widespread type of plant-fungus-interaction, the arbuscular mycorrhiza (AM).
The study aims to evaluate the controversy discussed mycorrhizal status and for the first time the mycoheterotrophic status, of the early vascular plant clade Equisetum at least showing habitat-dependent AM.
Material and Methods
Microphylls and spread leaves of six Equisetum species and fully autotrophic co-occurring reference plants (RP) were collected in NE-Bavaria, Germany. Carbon and nitrogen stable isotope natural abundances were analysed (EA-IRMS). Additionally, for E. palustre and E. sylvaticum and their RPs hydrogen and oxygen stable isotopes were measured (TC-IRMS).
Fungal colonisation was found for Equisetum roots (staining approach). Microphylls of Equisetum were enriched in 2H, 13C and 15N and mostly had higher nitrogen concentrations compared to RPs.
The isotope abundance and nitrogen concentration patterns found for Equisetum are known from green orchids and pyroloids to indicate partially MH carbon and nutrient gain. Thus, Equisetum should be considered as a new clade of partially MH plants.
During the era of the Carboniferous coal forests, 30‑m‑tall scale bark trees overtopped 10‑m‑tall Equisetum ancestors. The potential of mycoheterotrophy could explain their carbon gain under these light-limited conditions and their restricted photosynthetic active leaf area.