In the mycorrhizal symbiosis plants usually exchange photosynthates for mineral nutrients acquired by fungi. This mutualistic arrangement has been subverted by plants producing dust seeds and relying on fungal hosts for carbon supply in the seedling development stage (initial mycoheterotrophs, IMH). A few hundreds of IMH plants remain achlorophyllous as adults and continue relying on fungal carbon (full mycoheterotrophs, FMH). During the last decade additionally an increasing number of green plants has been identified as gaining carbon simultaneously from two sources, own photosynthesis and mycorrhizal fungi (partial mycoheterotrophs, PMH). Here we aim separating mycoheterotrophic plants not only according to their respective functional groups (IMH, FMH, PMH), but also according to their taxonomic relationships and to the functional groups of their respective fungal hosts.
Material and Methods
We used a stable isotope abundance database of mycoheterotrophic and accompanying autotrophic plants and molecular data on the identity of the mycorrhizal fungi to test the different functional groups for significance of differences in their isotope abundance patterns.
We succeeded in separating IMH, FMH and PMH from autotrophic plants. We furthermore separated (i) FMH from PMH, (ii) FMH associated with ectomycorrhizal, saprotrophic litter- and wood-decomposing and arbuscular mycorrhizal fungi, (iii) PMH on ectomycorrhizal basidiomycetes, ectomycorrhizal ascomycetes and rhizoctonias and (iv) FMH and PMH orchids and ericoids.
Isotope natural abundance is an ideally suited tool to elucidate fungus-to-plant carbon fluxes and to identify functional diversity among mycoheterotrophic plants. Mycoheterotrophy in mycorrhizal symbioses is much more widespread and diverse than previously assumed.