BayCEER Workshop 2023

Do common woody seedlings in the understory of tropical forests exhibit partial mycoheterotrophy?

Some chlorophyllous understory species with Paris-type arbuscular mycorrhiza in temperate forests are capable to gain carbon (C) from their mycorrhizal fungi, suggesting that partial mycoheterotrophy – where plants gain C from fungal partners additionally to own photosynthesis – might be globally much more common than previously thought (Giesemann et al., 2020, 2021). Paris-type morphology is considered a requirement for fungus-to-plant C transfer (Imhof, 2009). Tree and shrub saplings in tropical forests are candidates for partial mycoheterotrophy based on mycorrhizal morphotypes (Dickson et al., 2007) and due to their severely light-limited habitat.

Using stable isotope and microscopic techniques, we examined whether common shade-tolerant tropical tree and shrub species are partially mycoheterotrophic as saplings. Own observations of fungal morphology within plant species (n=40) disagreed somewhat with the literature (Dickson et al., 2007), indicating the demand for in situ determination. Enrichment in the heavy isotopes ¹³C, ²H and ¹⁵N (cf. mycoheterotrophic Voyria) relative to surrounding plants reflected a partial mycoheterotrophic nutrition of at least one Paris-type target species. Although our data do not support fungi as a prevalent C source, differences in stomatal regulation and transpiration of plants might have led to an underestimation of a heterotrophic part of nutrition in some species.