Orchids? We’ve all heard of them! But did you know that some of them are not only photosynthetic, but also need help to produce the simple molecules they need? They live in symbiosis with other plants or with fungi. The metabolic pathways are not yet fully understood, nor are the transit times from one individual to another. 14C dating can shed light on some of these unknowns, and this was the subject of the study we developed with two colleagues from the Muséum National d’Histoire Naturelle.
Mycorrhizal symbiosis, a widespread mutualism over 400 million years old, consists of soil fungi associated with plant roots. In this symbiosis, mineral nutrients from the soil are exchanged for photosynthetic products. As plants have evolved, the fungi involved in this association have diversified, and the exchange has been modified in some cases. Several groups of achlorophyllous plants associated with fungi have emerged independently, reversing the ancestral flow of carbon. So-called mycoheterotrophic plants exploit the carbon substrates of their fungal hosts. These fungi obtain their own carbon from other sources: some are saprophytic and exploit dead organic matter, while others are mycorrhizal on autotrophic plants that provide carbon and energy for the entire consortium. In tropical zones, we showed that the carbon feeding Wullschlaegelia calcrata had left the atmosphere 8.4 years previously, passing through litter and decomposing fungi, and that the transit time for Voyria aphylla was 4.3 years, passing through tree roots and associated mycorrhizae. In temperate zones, transit times are slower: less than a year for Cephalanthera damasonium, Neottia nidus-avis and Hypopitys monotropa associated with beech trees.
Christine Hatté, Antoine Zazzo, Marc-André Sélosse, 2020. The radiocarbon age of mycoheterotrophic plants. New Phytologist, doi: 10.1111/nph.16637
