Use of radiocarbon for assessing the mycorrhizal status of mycoheterotrophic plants.

Mycoheterotrophic plants are non-photosynthetic plants that obtain nutrients from fungi. Even though most of these plants are associated with the mycorrhizal partners of surrounding photosynthetic plants, recent studies have suggested that some mycoheterotrophic orchids indirectly obtain carbon from decaying organic matter through associations with saprotrophic fungi. However, such suggestions have been based primarily on indirect evidence, such as the 13C and 15N abundances of fungi and plants. It was recently reported that some mycoheterotrophs yield elevated Δ 14C values, owing to the indirect acquisition of 14C-enriched bomb carbon from dead wood. The approach was based on the anthropogenic change of Δ 14C values; atmospheric CO2 were globally elevated by nuclear weapons testing in the 1950s and early 1960s, but have steadily declined since its peak after the atmospheric nuclear test ban treaty of 1963. The study has provided novel evidence that mycoheterotrophic plants can exploit both mycorrhizal and saprotrophic fungi. We suggest that the radiocarbon analysis is also useful for investigating the nutritional modes of mixotrophic plants as well as for investigating whether the recruitment of wood-decaying fungi into novel mycorrhizal partnerships preceded the evolution of full mycoheterotrophy.