Stable isotope analysis indicates partial mycoheterotrophy in arbuscular mycorrhizal woody seedlings in tropical forests

Abstract

Chlorophyllous plants exhibiting partial mycoheterotrophy obtain carbon through mycorrhizal interactions in addition to photosynthesis. In arbuscular mycorrhizal (AM) plants, the Paris-morphotype (i.e. hyphal coils) is considered essential for mycoheterotrophic carbon gains. Numerous tree species in tropical lowland forests form this morphotype, and under light- and nutrient-limitation, additional carbon gain would be beneficial. However, if seedlings of woody species in the understory of tropical lowland forests exhibit partial mycoheterotrophy remains unexplored. Here we (a) examined the AM morphotype (Paris- or Arum-type) in seedlings of 41 tropical woody species, and (b) to determine if any of the target Paris-type species are partially mycoheterotrophic, we compared their multi-element stable isotope natural abundance (13C, 2H, 18O, 15N) with neighbouring autotrophic non-Paris-type reference seedlings. About 50% of the investigated species (and 80% of the genera) exhibited the Paris-type, expanding the number of tropical plant genera with Paris-type AM. Enrichment in 13C, but not in 18O in target compared with neighbouring reference plants indicated partial mycoheterotrophy in seedlings of 6 of the 21 investigated Paris-type AM species. Our results indicate for the first time that carbon gain through mycoheterotrophy occurs in seedlings of AM tropical tree species. In tropical forests, partial mycoheterotrophy during seedling establishment may confer so far unrecognised ecological advantages influencing seedling recruitment and ecosystem dynamics. Read the free Plain Language Summary for this article on the Journal blog.