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In contrast to mycoheterotrophs that associate with ectomycorrhizal and saprotrophic fungi, we know little about the ecophysiology of arbuscular mycorrhizal mycoheterotrophs. Here, we identify the mycorrhizal fungi of two unrelated mycoheterotrophs and one putative partial mycoheterotroph that form arbuscular mycorrhizas, and analyse their carbon (C) and nitrogen (N) isotope signatures., We used molecular methods to identify the mycorrhizal fungi of Dictyostega orobanchoides, Burmannia capitata (Burmanniaceae) and Voyria aphylla (Gentianaceae). Their C and N sources were investigated by analysing their stable isotope natural abundances (δ13C and δ15N). In addition, four putative partially mycoheterotrophic Burmannia species were grown ex situ., We found that both mycoheterotrophs and a green Burmannia species are associated with nonoverlapping Glomeromycota fungi. The investigated mycoheterotrophs are significantly more enriched in 13C than co-occurring autotrophic plants but lack significant 15N enrichment. The green Burmannia species is not significantly enriched in 13C and 15N compared with surrounding plants and can grow fully autotrophically under controlled conditions., Our results suggest that mycoheterotrophic Burmanniaceae and Gentianaceae are able to exploit arbuscular mycorrhizal fungi. Green relatives of mycoheterotrophic Burmanniaceae from high-light grassland sites also associate with arbuscular mycorrhizal fungi but we found no evidence that they receive detectable amounts of C from fungi. [ABSTRACT FROM AUTHOR]

Afrothismia winkleri develops fleshy rhizomes, densely covered with small root tubercles, narrowing to filiform roots with age. The exclusively intracellular mycorrhiza fungus has distinct morphologies in different tissues of the plant. In the filiform root the hyphae grow straight and vesicles are borne on short hyphal stalks. The straight hyphae are present in the epidermis of the root tubercles, but change to loosely coiled and swollen hyphae in the rhizome tissue. No penetration from epidermis to root cortex was found. From the rhizome a separating cell layer permits only one or rarely two hyphal penetrations into the cortex of each root tubercle. The hyphae proceed apically within the root hypodermis in a spital row of distinctively coiled hyphae, branches of which colonize the inner root cortex. In the inner root cortex the hyphal coils degenerate to amorphous clumps. In order roots the cortex itself also deteriorates, but epidermis, hypodermis endodermis and central cylinder persist. The mycorrhizal pattern in A. winkleri is interpreted as an elaborate exploitation system wherby the fungus provides carbon and nutrients to the plant and, simultaneously but spatially distinct, its hyphae are used to translocate and store the matter within the plant. Several features indicate that the endophyte is an arbuscular mycorrhizal fungus. [ABSTRACT FROM AUTHOR]