Arbuscular mycorrhiza (AM) is a symbiosis between plants and Glomeromycotina fungi, distributed throughout the plant kingdom and all terrestrial ecosystems. Colonization in plant roots takes structural forms of either Paris- or Arum-type, distinguished by intracellular hyphal coils and arbuscules, respectively, with a near 1:1 distribution among plant species.
Recently it was shown that green Paris-type species reveal a mixed isotope pattern of half-plant, half-fungus, due to a 13C and 2H enrichment. This pattern is known for partial mycoheterotrophic (PMH) plants gaining carbon from photosynthesis and on-top from fungal origin. Now, a speculation evolves, that 50% of all AM plant species are potentially PMH, however, we suggest that it is restricted to the light availability (e.g. shady habitats) and lifeform (e.g. forest herbs).
Material and Methods
Colonization patterns of AM plants were gathered from Dickson et al. (2007). Mycorrhiza, 17(5), 375-393. Ellenberg’s indicator values (EIV) and lifeforms were included, allowing to compare 128 Arum-type to 65 Paris-type species. Subsequently, a literature survey enabled the comparison of 13C data for 50 Arum- and Paris-type species.
EIVs showed a significantly lower light availability for Paris-type relative to Arum-type species. Although the difference of only 0.6 is small, a dependency on the lifeform was discovered (e.g. forest-ground geophytes, 1.1). Paris-types were significantly enriched in 13C. This was not correlated with light availability through the whole dataset, however, tendencies for geophytes (r2 = 0.5) drew some attention.
Paris-type species occupy habitats with low light availability. The possibility of mycoheterotrophic carbon gain through the fungus could be an advantageous compensation in a shady environment and clearly sets them apart from Arum-type species. These very first results contribute to our understanding of mycoheterotrophy and its significance for AM plants.